Lightning Protection Institute


FREQUENTLY ASKED QUESTIONS
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Frequently Asked Questions

If a home is located underneath the canopy of trees, should the trees have conductors to protect from falling branches or other harm to the home?

Is it possible for lightning to hit the roof on your home, go through it and through the ceiling and hit your top floor as a direct hit while you are inside? Or does it just hit your roof and circumnavigate your home?

Could you supply me with information on how close a vehicle can be to a lightning bolt before this vehicle will or may have electrical problems?

We have no specific testing information on lightning and vehicle electronics. Certainly we recommend that individuals seek safety from exposure to direct lightning strikes by insulating themselves within a vehicle when a building is not close by, and we are aware that direct strikes may cause some electrical problems for a vehicle. The question about how near a strike could be depends on a lot of variables. When lightning strikes a lightning protection system it is carried from the roof mounted strike termination devices to the grounding system on cable conductors. When these cable conductors become energized we need to assure that no side flashing or jumping to other building grounded systems occurs, so we bond or interconnect all systems with the lightning protection system to equalize potential. A secondary effect of this energy traveling along the conductors is the induction that can occur to other lines or systems in close proximity from the magnetic flux created. This is extremely difficult to quantify, since there is great variability in the energy in individual lightning strikes, variability in the number of paths the lightning may split and follow through or on a structure, variability in the proximity of systems that could be effected to the lightning conductors, and variability in the amount of induction that could show some appreciable effect in another system. The lightning protection system is required to have surge suppression at all entrances to protect the structure from lightning entering on energized lines, and in most cases critical internal equipment will be additionally protected from inductive effects by suppression equipment - just in case. The fact that most vehicles would be isolated from the environment (at least the ""electrical"" environment of earth ground) by insulating materials (non-metallic tires) makes the determination of the impact of ""close"" strikes even more problematic. Of course other ""vehicles"

ABOUT LIGHTNING

Where does lightning come from? Does lightning start from the ground and travel upwards, or does it start from the sky and travel downwards? And why does that happen?

Does lighting make a sound before it hits the ground?

What are the consequences of indirect lightning?

Where can I find the best photo gallery and information on lightning?

""...a lightning protection system will not attract a bolt of lightning."" Does this mean that if you have two arrestors on your roof, 10 to 20 feet apart, that the lightning bolt could come down right between the two arrestors?

On an overcast day last year, we observed from the safety of the house, a ball of light about 15 feet above the ground. It appeared to be a gigantic flash bulb, about 2 basketballs in size. There was no sound and no apparent damage anywhere. Is this lightning?

I’ve always been worried about flashovers. Can you tell me more about them?

How far can lightning travel in salt water? A friend told me he heard on TV that it can travel 5 miles.

I work for the Safety Department and am concerned about lightning striking close to our building that could travel through the ground and into the building potentially affecting an employee. Will the effective ground provided around the building prevent such an occurrence?

Step potential deals with the effect of lightning spreading out over the surface of the earth to neutralize its charge imbalance. In soils with good electrolytic or high moisture content (clay, loam soils) it spreads out over a smaller area than in poorer soil conditions (rocky or sandy soils). This situation leads to an ""electrified grid"" of earth for a short duration. Someone standing in the affected area would have a difference of potential between their feet, dependent upon how far they are spread apart, and thus a current flows in the body. This is why many times a person in the vicinity of a strike gets knocked off their feet. A person lying on the ground may suffer more severe consequences, since more critical body parts may receive this current flow. Because of this same effect, isolated grounds for systems may pick up the ground charge at different time intervals, causing a difference of potential within a structure. If any electrical ground and a communication ground are connected to the same internal piece of equipment, the difference of potential will cause a current flow within the equipment, which may lead to damage in equipment or a hazard to personnel operating the equipment. This is the reason for interconnecting all grounded systems that enter a structure, along with structural framing and things like metallic water or gas piping to create a common ground. Surge suppression is also used to provide an equipotential bond for active service lines entering a structure that cannot be directly connected to ground. Besides common grounding of internal systems, two methods prove effective in creating a safer interior workspace for personnel. A ground conductor loop can be installed encircling the structure with connections to the grounded systems, incoming piping, and structural framing members, whether they are steel columns or reinforcing steel in poured columns. A structural lightning protection system would terminate at this ground loop. In this way all direct strikes and strikes outside the area would cause the loop conductor and any items attached to see the potential rise and fall at the same time casuing little effect internal to the loop. In a situation where a concrete slab is poured under the structure, the rebar can be interconnected to the loop at 100 ft. intervals around the perimeter, which will enhance the total grounding of the systems and provide equal potential for personnel standing on the floor. Most other forms of flooring are insulating by nature. In areas where there is only an earthen or gravel base, the loop is still fairly effective at maintaining potential within its boundaries. In applications where major fault currents could be expected, such as at a transfer station for an electric utility, a grid of conductors is laid below the earth to provide additional personnel protection. Again this grid allows for the rise and fall of potential equally, creating additional personnel safety. We often see this method used on small prominent structures where people go to avoid storms, like golf or picnic shelters.

How could lightning have hit a home not as tall as surrounding homes and/or trees and have blown out roof sections near the ventilation jacks?

Lightning is a fairly random occurrence. It may not strike what you would consider the most likely target, but there are some parameters that we use. If we provide a complete lightning protection system on a structure, strike termination devices and conductors to a grounding system, the Standard consider this to provide a ""protected zone"" based on a 150 ft. radius sphere model. A 150 ft. radius curve, tangent to a lightning rod at the top and to earth at grade, provides shielding to items under the curve. To give you a simplified idea of distance, at lower elevations this replicates a 1 to 1 relationship, so a lightning rod mounted on a 30 ft. tall roof protects about 30 ft. out on the ground. It is important to understand that height may break the curve, so if you are 6 ft. tall and standing on the ground, you would need to be within 8 ft. of the 30 ft. tall building to be below the curve and not subject to a direct strike.You may have the idea that tall items within every square mile will take all strikes, but this is obviously not true from the zone of protection parameters used in the Standards. Protecting a structure really protects only that building and a small surrounding area. If there is not protection in place, then height, the ability to release ions, and conductivity give clues to lightning attachment probability. Trees may be tall, and have pointed appendages to release ions, but they are not very conductive. There are many items in residential construction that can provide superior paths to ground - like the electrical service, plumbing piping, gas systems, and phone systems - so a structure may be a better candidate for a strike. We would also note that two houses 30 ft. apart have little effect on each other. Again, the randomness of attachments comes from the fact that lightning cannot be attracted to anything over any great distance, even a complete protection system.

CERTIFICATIONS AND PROGRAMS

I have a specification that states..."" Install a UL Listed or LPI Certified lightning protection system."" Does LPI issue a certification for an approved lightning protection system installation?

What is the process for becoming a ""Master Installer"" through LPI?

How do I become a ""Professional member""? What are the costs and benefits? How can I check over the system before the installation process?

If you are to review plans prior to construction for completeness, then you will need to fully understand NFPA 780. We have a sister document LPI # 175, based on 780, with additional information geared toward the installing contractor. These tools will give you guidance in developing a checklist for plan review. We have an additional program called the LPI Certified System, which provides documentation of the system as it is installed. The installing contractor and project engineer or owner’s representative sign off on three stages - including the in-ground system components, the concealed in-construction components, and finally the above roof or exposed components. Again, this is not pre-construction, but it will give you many of the items you should look for in a complete submittal. Underwriters’ Laboratories, Inc. (UL) has a program for third-party field inspection of completed lightning protection installations to their Standard UL 96A (based on NFPA 780). They also do in-factory inspection with labels attached to components qualified to their lightning protection materials Standard UL 96. LPI has adopted the UL materials listing and labeling program to approve quality of system components.The Professional Division of LPI includes engineers, inspectors, scientists, and others not directly involved in the lightning protection business, but associated with it. We provide a free copy of our Standard (LPI 175) to our members, along with Tech Letters dealing with design aspects of lightning protection, a Newsletter covering association subjects pertinent to the members, other informational pieces on lightning and protection, and listing on our website for user reference. We have an annual conference where educational items of interest are discussed, and you have a chance to meet and learn from others in the industry. We also have an examination program - Designer-Inspector Certification- for professionals including 2 x 2 hr. exams to show competence with the Standards. Please refer to the “prospective member info” on this website for more information.

What is the time frame from application to Board approval once a company has applied and paid the dues?

Can an engineer take the Master Installer/Designer certification test without completing the Journeyman and Master Installer certifications first?

What is the time frame from a company becoming an Affiliate member before tests can be taken through a proctor?

What exactly is a Master Label? Is it registered with a particular organization?

The LPI contractor we have hired has informed us that LPI will not certify a Catenary system. Is this correct information?

Is an architect required to consider lightning safety when designing a structure?

Whether or not something is required in building standards depends on the requirements of the local authority having jurisdiction. In many cases this is an entity like city or county government and it is totally dependent on what Codes or Standards that body has adopted. There is no ""national"" law requiring lightning protection. There are some state laws regarding particular types of occupancies - for example, Florida requires lightning protection on health care facilities. The National Fire Protection Assoc. (NFPA) publishes a Standard for the Installation of Lightning Protection Systems (# 780) which can be adopted by any jurisdiction just like any other Code or Standard of practice. The National Electrical Code (NEC or NFPA # 70) & Life Safety Code (NFPA # 100) are a couple of the better known documents published by NFPA along with literally hundreds of other documents in the fire safety field. None of these is required unless some authority has adopted them specifically into local law. NFPA 780, the lightning protection document is a stand-alone document that is not required by other building Codes, but is left to local option. That doesn't mean that having a working knowledge of these codes and standards isn't a good idea if you are a professional. Architects have a code of ethics just like any other professional which should require them to make clients aware of any product, service or system that may be to their benefit. In many cases an architectural firm may have a list of various items to review with prospective clients early on in the planning stage of a project. Based on this type consultation any system not covered automatically by law may be valued in or out of a project to the satisfaction of the customer. In areas of the country subject to high lightning activity, or in construction occupancies where evacuation is difficult, lightning protection would be an important consideration on any project.

I’m trying to prepare a scope of work to bid out lightning protection for two apartment complexes. I’ve heard there are different types of standards and certifications for lightning protection. Is there anything you can send that may help me know what specifications the lightning protection system needs to meet?

What does the National Electric Code (NEC) say about lightning protection for buildings? Is it only required for certain types of facilities?

INDUSTRIAL / COMMERCIAL BUILDINGS

What is there to know about lightning protection systems for commercial airports?

In adding on to a structure with a preexisting lightning protection system, is there an added risk to the new addition?

Is there any information regarding lightning protection systems for a mast mounted on the top of a building?

What is the risk of a lightning strike to a high-rise building with antenna equipment installed?

The risk for lightning strikes and damage to a structure are best determined using the National Fire Protection Assoc. (NFPA) Standard # 780 Annex L. This provides a mathematical model to make a determination. The Annex considers the effective area of a structure for lightning strikes, the lightning frequency for it's locale, and the potential for loss based on construction, contents, and occupancy. Using the above you can determine the need for lightning protection on a high-rise condominium. We would suppose there is some minor difference in height between the building with and without the cell phone antenna, but doubt that this will make much difference for comparison. There is generally no more or less incidence of lightning attachment to structures that do or do not have lightning protection systems. Lightning is going to strike so many times on average in a square kilometer each year. However, if you have a complete lightning protection system, then you aren't concerned about lightning striking your property. Lightning protection is a passive grounding system - including strike termination devices, interconnecting conductors, a grounding system, interconnection to other building grounded systems, and surge suppression. Although we know that tall slender items release ions more freely than a large flat roofed area and, therefore, are more likely for lightning attachment, antennas aren’t substantially more attractive than other building appurtenances. In the competition for the lightning attachment point, building corners, edges, mechanical vents, and many other roof-mounted items may be considered slightly more or less likely targets to an antenna. We do know taller items are more likely to be struck than low-profile bodies, so all antennas should be considered for bonding into the lightning protection system protecting the entire roof area. Any antenna wiring that enters the structure may be considered a possible entrance point for lightning, and should be addressed with proper protection using surge suppression equipment or appropriate grounding techniques.

I’m putting up receivers for cameras on top of buildings and they have to be grounded. There is existing lighting protection around the roof. Can I attach my ground to that cable? Or if I run alongside of this cable and ground to something else will it be affected if the lighting protection gets hit?

There are a couple of situations to consider in your application. If the receivers are as tall or taller than the lightning protection system’s components (strike termination devices), they are subject to a direct strike. If they are metallic and made of metal 3/16"" thick or more, they can serve as strike termination devices and simply need to be bonded or grounded into the existing system. Alternately, if they are not ""thick"" enough or not metallic, they may be placed under a zone of protection of strike termination devices so that lightning will not attach to them directly. The second item is the line or lines running between the receiver and the interior camera monitoring devices (we presume). If lightning attaches to the bonded receiver or to an adjacent lightning protection system, there is a good chance stray voltage will be induced into the lines. Lightning has tremendous levels of energy and sets up lines of magnetic flux surrounding any conductor that it travels. Any service line near this lightning event will pick up some of the energy by induction (there is no way to isolate them), and with low-voltage circuitry there is a good chance for damage to connected equipment. To address this situation you will need surge suppression designed to work with the voltage and equipment in use, probably supplied or recommended by the system manufacturer. Finally, make sure that the lightning protection grounding system, the electrical grounding, and any communications grounds are tied together at or below grade level and at roof level. If they are interconnected, a common ground plane will exist so that overvoltage situations allow equipment connected to more than one service to rise and fall together. If grounds are not common, rising and falling potential at differing times may cause stray currents through equipment causing damage or shock to an operator.

I have a handrail that runs around the perimeter of a six story building. The handrail is 1’ 4"" above the parapet. The top of the rail is 6"" wide by 3/4"" thick flat rail. Can I use this for lightning protection? Can I add short rod points to the top of the rail?

I would like to know if LPI has any recommendations or procedures that a local Park and Recreation Department should follow concerning the public in an indoor pool during a lightning or thunder storm? Should the pool be evacuated or can the public remain in the pool during a storm?

Indoor pools certainly have a lot of variables to consider under lightning attachment conditions. If the facility structure has a complete lightning protection system in accordance with the national Standards, then I believe that the individuals inside are as safe as we can make them, regardless of the internal systems or functions of the construction - that is the easy answer. If there is no lightning protection system, then we need to consider what path the lightning will follow to reach earth ground. It could be along structural framing members outside the perimeter of the pool itself, or it could seek metallic piping systems, or equipment wiring that provides paths to ground. There is no control mechanism without a protection system for the building, so lightning may seek any number of paths depending on the actual attachment location and the available conductive paths or lack thereof. A secondary problem is arcing between separately grounded systems. When one metallic system becomes energized by lightning or anything else, any other independently grounded system will be at a different ground potential. Different ground potentials cause current flow, either within equipment connected to two or more systems, or if they are proximate, arcing may occur through the air or building materials. Bonding these various grounded systems together at their entry to structures, and at point where equipment interconnects multiple systems, minimizes any potential difference problems, and is now required by the National Electric Code (NFPA 70), as well as the lightning protection Standards. But I think your interest may be more directly related to how the pool water itself may become involved in this equation. Distilled water does not conduct electricity. You may remember a 7th grade science class, where you tried to use a battery to power a lamp with leads run through a jug of distilled water. The problem is we don’t use any pure water. The salt water in the ocean is a much better conductor than fresh lake water because of the level of particulate matter that conducts electricity, but they both conduct. Our drinking water is treated for ""purity"" and these particles conduct. Swimming pool water is further treated to inhibit bacterial growth, which adds potential conductive capability. Now we are faced with so many variables it becomes pretty difficult to provide a strict analysis to conclusion. How conductive is the pool’s water? What grounded systems are attached to what points of the pool water? Where is the lightning coming from, and where will it head to earth ground? This makes it difficult to provide any blanket statement about personal contact with pool water, either outdoors or in an indoor unprotected structure. It is so difficult to predict with accuracy, that most authorities will implement policies of clearing a pool under storm conditions to mitigate any potential contact between a really good conductor (the human body) and the potentially conductive pool water. Now that you have cleared the pool you have the next problem to deal with - human nature. Your patrons go into the shower room and stand near the metallic plumbing system and the metallic drainage system. They get on the phone to call for a ride, and landlines provide a path for lightning to follow. People run out to their cars in the parking lot, and expose themselves to direct strikes (until they get into their cars where they are relatively safe). It is not an easily solvable situation. Frankly, if you don’t have a control mechanism to handle lightning, it has control of you.

Is it proper to use interior roof metal roof drains as air terminals and the metal drain pipes as the downleads in a lightning protection system? In addition, some of the interior roof drain caps are directly connected to the main conductor along the roof parapet lightning system. The perimeter parapet walls have proper air terminals and downleads terminating directly into the ground.

Normally roof drains and internal piping systems are not considered the main current carrying parts of a lightning protection system. The roof mounted access points do not generally rise to a level of prominence to protect the nonmetallic roof structure for any great distance, and the conductivity and continuity of the drain piping is questionable since it is not designed to be an electrical conductor. A more likely scenario is the drain system represents a valid alternative ground path to the lightning protection system, so we need to be concerned about lightning leaving the protection system and seeking these alternative paths to ground. Any long vertical metallic system within a structure that terminates in the earth creates the possibility for lightning to sideflash from a system toward a ""better"" ground path. To assure that lightning travels the system designed for the purpose, the Standards require the interconnection of all grounded systems with the lightning protection ground system at grade level. This includes electrical grounds, communication grounds, water piping, gas piping, and metallic drain lines, etc. This potential equalization for all grounded systems is the main bonding requirement of the lightning protection Standards. As these systems rise to various vertical heights and proximities to the lightning protection system components, we must determine a bonding or sideflash distance appropriate to that point. We do this by a formula that takes into consideration the number of proximate downleads to ground, the height from the last lower bonding connection, the material through which the lightning would need to pass (air or building material) and determine whether the bonding distance requires an additional bond or lightning will not jump the gap. In many cases, bonding all internal systems at roof level (along with the required grade level bonds) creates potential equalization throughout the structure. (On extremely tall structures, the Standard requires a mid-height loop at 200 ft. vertical intervals interconnecting all grounded systems.) This is not a function of designing the lightning to be carried on alternate paths, but really keeps the lightning from leaving the system with potentially hazardous results. Although it is more involved today, it used to be fairly typical for items like roof drains to be bonded to the system when they were within 6 ft. of any system component. This assumed the lightning would potentially jump 6 ft. through air but no farther, so items exceeding this distance were not bonded or beyond the sideflash range.

I have a building with a mansard type roof with the lower eave more the 50’ above grade. If I place lightning rods around the upper edge of the mansard, spaced accordingly, will this provide me proper coverage for the lower area of the mansard roof, or should I use the rolling sphere model to determine coverage areas? Will the rods at the top of the roof provide the coverage for the lower eave?

An approximate 300 ft high ""open-structure"" Boiler Building is currently under construction. With many days of in-climate weather at this time of year, we experience severe thunderstorms and lightning. The boiler structural steel is grounded in approximately 20 places. It will be 2 to 4 months before a temporary roof is installed and siding operation started. From a corporate standpoint, what can we do to ensure the safety of the personnel working in the building?

Any metal body 3/16"" thick or greater can be substituted for a strike termination device or cable conductor. 3/16"" thick metal will not burn through when lightning attaches and it certainly has enough free available electrons to carry the lightning to a grounding system. Most lightning protection systems on structural steel buildings have a system of air terminals and cable conductors to protect the insulated building materials used for roofing, with connections just below roof level to the continuous steel beams or columns, which are then grounded at grade level. During the construction process the extended steel columns may be grounded to provide ""temporary"" lightning protection for the project. A metal framed crane located above the construction area can be grounded as well to not only provide safety for the operator, but also a prominent strike point for lightning to help protect the surrounding area. Personnel protection from direct strikes depends on the relative location of workmen and prominent grounded steel. Protected zones according to NFPA 780 are described by a 150 ft. radius sphere model, tangent with the top of the steel and another steel member or the ground. This is how air terminals are laid out on rooftops, to support the 150 ft. radius sphere without it touching the roofing materials. Areas under the curve are considered to be immune to direct strikes. Another area of concern may be whether the workmen are in contact or working on continuous steel members at the time of a strike to the framing. If the steel is well grounded, then it should be the best and most direct path to ground and the lightning will typically follow it. Although the human body is an excellent conductor, it may not provide a preferred path or short circuit path as compared to the grounded steel. An individual on a low beam may replicate a ""bird on a wire"" where the potential at their feet remains equal, so no effect is felt.

I am looking for some help regarding code interpretation, concerning dead-end conductors. Specifically, my question concerns exhaust stacks mounted on the roof. In this case the stacks are typically about twenty feet high. In determining the allowable length of a dead-end conductor, do we measure from the air terminal mounted on top of the stack, or do we measure from the base of the stack to the main conductor run to which the dead-end is connected?

Paragraph 4.8.8.4 of the current edition of NFPA 780 reads, ""Where only one strike termination device is required on a chimney or vent, at least one main-size conductor shall connect the strike termination device to a main conductor at the location where the chimney or vent meets the roof surface and provides two or more paths to ground from that location in accordance with Section 4.9 and 4.9.2."" This seems to be a pretty clear answer to your question, regardless the height of the vertical structural member, there is no dead end - once it reaches the roof surface a two-way path is required. In reality there is no vertical height limit for the single conductor, just like there is no maximum height of an air terminal. There would truly be no difference between mounting a 20 ft. solid rod point to the roof, and mounting a 12"" point with 19 ft. of vertical conductor, since these items are designed to be equivalent. What is very clearly specified is that when you leave the vertical, you are to provide a two-way horizontal and downward path, just like for any other air terminal in NFPA 780. Interestingly, NFPA only has a dead-end exception for roofs lower than the main protected level in Par. 4.9.2, which allows 16 ft. dead-ends. It has become a common practice to allow an 8 ft. dead-end on main roof levels, which I think started with a UL inspection allowance, and has been printed in the latest edition of LPI 175, but has never appeared in NFPA 780. I guess the answer to your questions becomes what Standard you are following. If you are following UL & LPI, then I would say you could go 8 horizontal feet to a 2-way path conductor on the main roof, but if you must meet NFPA, then you need 2 paths at the base of the vertical run. In either case, the vertical height of the single conductor is a non-issue. The only reason we provide multiple paths is to lower the lightning intensity on any individual conductor to lower the sideflash or bonding distance, but on a vertical body that requires only one point there isn’t anything else for the lightning to sideflash to.

INTERNAL SYSTEMS IN BUILDINGS

What are some simple recommendations for lightning protection equipment in a location where severe storms are frequent?

We do not know what type structural lightning protection system you are using for direct strike protection, but assuming you have one, and it is effective, there are two possible things that will enhance the system and possibly help with your problems. In many cases damage to interior electronic devices is a bonding problem. Equipment connected to 2 or more different systems can ""see"" different voltages from ground wires for separately derived grounds, creating a difference of potential and an internal current. When you drive a ground for a telephone system and another for the electrical system, they should be interconnected. When lightning strikes anywhere, it will eventually reach the earth's surface and spread out to neutralize itself through the electrolytes in the soil. The poorer the soil (lack of moisture, low electrolytic content), the further it will spread, and the more items it may come into contact with. As the lightning spreads it will reach different ground rods at a different time interval, and back feed into the structure. This creates the potential difference within the connected equipment that may lead to damage. A complete lightning protection system is enhanced by a ground loop encircling the structure. This loop will connect to all the lightning protection system grounding devices, any other system grounds (electric, telephone, data, etc.), any metallic piping systems (water, gas, sewer), and the building structural steel (reinforcing steel in concrete, or steel framing). This loop not only provides additional grounding medium to route a direct strike away from the structure, it provides potential equalization for everything inside the structure to stop side flashing within. Once all systems are tied together, the ground devices ""rise and fall"" at the same time, eliminating the internal difference in equipment. The second item is transient voltage surge suppression (TVSS) or arrestors. These devices ""ride"" the energized lines under normal operating conditions, but when they ""see"" an overvoltage situation they react to route the excess voltage to ground. They are required at the entrance of every system for a complete lightning protection system. But at entrances you can only clamp the voltage to a certain level, for example a 240-volt entrance would be clamped at the 380-500 volt range. This protects motors, appliances, wiring, etc., but may not clamp tightly enough to protect electronics. Electronic devices may require additional TVSS protection either in-line at their location or where they plug into the electrical system. A plug-in TVSS unit for a phone system should have a power protector and a phone line protector with a connection to ground in the same unit. Since suppressors or arresters must be sized to allow for normal operation of the equipment attached, you can normally get the proper items through the equipment supplier. Arrestors and TVSS devices are self-sacrificial, so they have a lifetime and become ineffective eventually. You may need to implement a maintenance program after installation, or you may find units available with indicator lights that advise their life is spent. You may wish to have an electrical engineer familiar with lightning, bonding and grounding survey the site and make specific recommendations.

What are the variables to take into consideration when talking about a phone system?

There are generally 3 conditions that can occur during a lightning event that may cause problems to someone on a ""hard-wired"" phone system. Surge suppression devices need to be installed on the incoming lines to prevent lightning from following the service into the building to individual phone equipment. These are normally placed at the entrance of the phone service to the building. This is why the lightning protection Standard NFPA # 780 calls for surge suppression at every electric, communication, or data entrance. If the grounds of the phone system and the electrical system are not interconnected, the different ground terminals may pick up a lightning event at differing intervals. When lightning disperses into the earth and gets picked up by grounds at different times, there can be a potential difference in any equipment connected to both grounds. So if your phone system has a power cord ground and a communication line ground at different potentials, you may have a stray current created within the equipment. Anyone in contact with the equipment at that time is at risk. This is why NFPA 780 calls for all building grounded systems to be interconnected with the lightning protection grounding system. Third, if there is no system of strike termination devices, cable conductors, and grounding to form a system of direct strike protection for a structure according to NFPA 780, then the lightning may follow any path to ground. The ""best"" path may include the metallic wiring to phone outlets interior to the structure. This can create a situation where surge suppression at the entrance would be of no use (the lightning is in the system beyond that point) and ""plug-in"" style suppression at the phone device wouldn't be sized to handle that much energy. It is nearly impossible to determine when it would be safe to be on the phone. There are so many variables to consider. Are you nearer the exterior or interior of the large office building? Is there a ""stepped"" system of surge suppression installed? Are the grounds properly tied together? Is there a complete functional lightning protection system in place on the structure? There is lots of variability, so general safety requirements normally tell you to stay off the phone during a lightning storm.

These days many people use cordless phones. Do lightning concerns only apply to phones plugged directly into the wall, such as landline phones?

How would a cordless phone be unsafe?

Is it true to stay off the toilet when a lightning storm is near?

Do lightning strikes affect electronics or appliances that are not plugged in?

Would you suggest or recommend that I replace all of my electronics, appliances, light fixtures, lamps, etc. after a strike?

I was wondering if you could give me any information on how to protect my house from lightning, when achieving a good ground is not an option? My house is on a ridge, on ledge, swamps, with a river nearby. In the past 4 years I’ve had over $10,000 in damage to electrical devices. I’m not sure if it is coming in through the ground or the power lines, it seems to be both. Some devices were destroyed even when unplugged. I’m even getting electrical snapping when the strike is miles from the house. What should I do?

We do not know what type structural lightning protection system you are using for direct strike protection, but assuming you have one, and it is effective, there are two possible things that will enhance the system and possibly help with your problems. In many cases damage to interior electronic devices is a bonding problem. Equipment connected to 2 or more different systems can ""see"" different voltages from ground wires for separately derived grounds, creating a difference of potential and an internal current. When you drive a ground for a telephone system and another for the electrical system, they should be interconnected. When lightning strikes anywhere, it will eventually reach the earth’s surface and spread out to neutralize itself through the electrolytes in the soil. The poorer the soil (lack of moisture, low electrolytic content), the further it will spread, and the more items it may come into contact with. As the lightning spreads it will reach different ground rods at a different time interval, and back feed into the structure. This creates the potential difference within the connected equipment that may lead to damage. A complete lightning protection system is enhanced by a ground loop encircling the structure. This loop will connect to all the lightning protection system grounding devices, any other system grounds (electric, telephone, data, etc.), any metallic piping systems (water, gas, sewer), and the building structural steel (reinforcing steel in concrete, or steel framing). This loop not only provides additional grounding medium to route a direct strike away from the structure, it provides potential equalization for everything inside the structure to stop sideflashing within. Once all systems are tied together, the ground devices ""rise and fall"" at the same time, eliminating the internal difference in equipment. The second item is transient voltage surge suppressions (TVSS) or arrestors. These devices ""ride"" the energized lines under normal operating conditions, but when they ""see"" an overvoltage situation they react to route the excess voltage to ground. They are required at the entrance of every system for complete lightning protection of a structure. But at entrances you can only clamp the voltage to a certain level, for example a 240-volt entrance would be clamped at the 380-500 volt range. This protects motors, appliances, wiring, etc., but may not clamp tightly enough to protect electronics. Electronic devices may require additional TVSS protection either in-line at their location or where they plug into the electrical system. A plug-in TVSS unit for a phone system should have a power protector and a phone line protector with a connection to ground in the same unit. Since suppressors or arrestors must be sized to allow for normal operation of the equipment attached, you can normally get the proper items through the equipment supplier. Arrestors and TVSS devices are self-sacrificial, so they have a lifetime and become ineffective eventually. You may need to implement a maintenance program after installation, or you may find units available with indicator lights that advise their life is spent. It is difficult to address all your possible problems from long distance. You may wish to have a lightning protection professional survey the site and make specific recommendations. You may click the ""Dealer-Contractor Locator"" on the homepage of this website to find a state-by-state listing of our member companies. There should be someone there to help or direct you further.

My grounding rods were installed close to my gas line. Should I be concerned?

I’m interested in information on lightning striking a satellite dish that is not grounded. What are the odds that the ungrounded dish would take a direct strike before the rest of the roof? Also, if the dish was struck, does this mean there would have to be apparent damage to the dish itself, or would the dish just conduct the charge and pass it through the co-axial cable?

There are a variety of factors to consider that are pertinent to where lightning might strike. Lightning will pull ions up from ground mounted bodies to complete the path that is the lightning strike. Things that easily release ions include pointed items like ridges, edges, or corners of different items, whether they are metallic or not. Metals normally have more free available electrons, so they are considered better release points than insulating type materials. A grounded metal body, or something that is the extension of a system that provides a preferred path to ground release ions more easily. Along with these items, tall or prominent objects are closer to the potential lightning, and thus come under additional pressure to release ions, regardless of their construction. A metallic satellite dish may include many of these factors associated with streamer release points. It can be metallic, and prominent to the surrounding roof areas. Even if it is not directly grounded into the earth, a coax cable may lead to equipment that is grounded through the electrical system, so it may be considered a better path than lightning following along insulating type building materials. Everything is relative in the competition between items to release streamers. A stone chimney located 30 ft. distant from a satellite dish could receive an attachment, even though it is not particularly conductive, because it may be taller and have a variety of edges and corners in a concentrated area. Metal bodies are very good conductors. In fact, a lightning protection system is an all-metallic conductor connected to the ground. Whether or not a lightning protection attachment will produce visible evidence depends on the thickness of the metal at the attachment point, the availability of a conductive path for the lightning to follow after attachment, and the intensity of the particular lightning event. Lightning strikes vary greatly in amperage and voltage, so the potential for damage is variable. The Standards will allow the substitution of metal with a thickness of 3/16"" for strike points or cable conductors in a lightning protection system. It can be shown that metals of this thickness will not ""burn-through"" from a lightning attachment, and that they will ""carry"" the lightning to a grounding attachment point with no deformation. Again, this is to handle most all lightning strikes, including the most violent, so lower level strikes could be carried by lighter metals with little apparent damage. Other locations where lightning results might be visible would be where the lightning left a conductive body or system and tracked through an insulating type building material. A lightning strike of nominal magnitude could track along wiring, like a coax, with little visible evidence, or a more violent strike could possibly disintegrate the wire.

MATERIALS IN L.P. SYSTEMS

Is the aluminum and copper combination as durable and safe as the copper only, and will it give us the same type and amount of protection?

Is there any guidance that would tell them the effect of a blunt end on air terminals?

Should we be concerned about a lightning protection system on an existing multi-story building where the grounding cables from the roof arrestors are grounded to the structural steel joists directly below the roof and which uses the building's structural frame, much of which is exposed to occupants as an architectural feature, as the grounding conductor pathway down to the lowest level where grounding rods are then cabled to the base of the building's structural columns?

Does each ground rod need to meet the 5-ohm minimum test with the 3-point tester or just the system as a whole?

NFPA 780 has no requirements for a minimum ground resistance on any terminal. It is more important to equalize ground potential on a lightning protection system, than it is to reach a specific value for grounding. When lightning strikes a system, we want the lightning to split along the multiple paths to ground provided by the system downconductors. This splitting minimizes the electrical force on any single conductor, which in turn lowers the magnetic flux that can induce stray voltages into other internal systems. If we provide driven terminals only, and there is great variation at the site from soil conditions at one corner to the opposite corner, then the lightning seeking the best path to ground will typically flow disproportionately to the better ground. The ground loop resolves this issue by placing all downconductors at similar ground potential. The ground loop or equipotential conductor should also be interconnected with all other building grounded systems or metallic piping systems entering the structure to resolve any issue of side-flashing between separately derived grounded systems. The problem with specific ground readings for any individual device or terminal is the variance in soil conditions for alternative sites. There is currently research being conducted on a test house with lightning protection at the rocket-triggered lightning facility associated with the University of Florida at Camp Blanding. In this sandy (poor soil) environment, individual driven terminals read in the range of 350 to 450 ohms. But they are the best ground paths in the area, so testing results show that is where the lightning follows to reach the earth. It is far more important to provide the ""lowest"" resistant path for lightning to follow to ground without any better option, than it is to achieve a specific value. System inspection should be geared to assure that over time, the grounding system still exists to serve its function. Certainly there is the potential for the ground system to degrade over time based on the materials and soil conditions. We recommend the system be tested every 5 years with records kept to show whether the system is deteriorating. It makes little difference what the starting values are, or whether you test individual devices or the entire ground system, as long as you have a consistent approach. There may, of course, be issues with testing the system related to how it can be disconnected from structural frame bonding and other grounding system interconnections that could give false readings.

What is the purpose of a test link in lightning protection?

A test link or disconnect for testing purposes normally relates to testing of individual ground terminals of the grounding system. In NFPA 780, listed disconnects are acceptable but not required. There are instruments or methods available that give an indication of the continued functioning of a ground or earthing device. It is most typical to use a 3-point earth resistance-testing device with remote earth contact probes, where a low voltage is sent back through the earth to the ground device in question and a reading is recorded. On the other hand, there are other devices that clamp around a rod or conductor and give readings. This is a reference source and would be acceptable for monitoring the life cycle of a ground device. Another possible option normally available in a basement is to compare the unknown ground device (item under test) to a known ground value. For example, a metallic water pipe system that extends out into the network of a city's water supply should have very low resistance. Instruments can be used to compare a separate ground conductor to the water system within the structure to do a comparative analysis. In fact testing one down conductor against the balance of the system is sometimes the only way to determine anything at roof level, which may be the only accessible point for conductor runs, concealed within building construction. The problem with using NFPA 780 is that the building structural steel must be interconnected to the lightning protection system top and bottom on each downlead or ground conductor, and all building grounded systems entering a structure (either separate ground devices or metallic piping systems) must be interconnected with the lightning protection system near grade level. This leads to so many ""ground"" connections, it is nearly impossible to isolate individual devices or the grounding system unless you provide a well at the individual ground device that can be accessed to disconnect and test at that individual point. There is always some question as to how significant an individual earthing device is to the whole interconnected system anyway. It is important to verify the continued existence of the grounding system, but disconnects may be optional in NFPA 780 because the system is much more than an individual device.

I’m looking for any information relating to the use of other types of wire to be used as a main conductor in a Class 1 system. Is there any reason not to use 7-strand #2 AWG THHN/THWN-type wire? It meets the NFPA minimums for strand size and total circular mils, but I’m wondering if there’s evidence to show that 29-strand cable is better? One might think the greater surface area would lower the impedance of such a cable due to skin effect, since lightning strikes have a very short rise time relating to a lot of high frequency energy. Also, an insulated wire with a white jacket is more easily hidden on a building exterior.

When should I replace the ground rods on my home’s lightning protection system?

Should conductors be installed in conduit on the outside of buildings leading down to the grounding rod or should they be left exposed?

NON-BUILDING SYSTEMS

Should people always evacuate pool activities, even if you do not hear thunder?

What is the coverage angle for a single pole (mast) that needs lightning protection?

For a communications tower, should we use an insulated conductor to connect the air terminal and the ground terminal or just a bare cable, which may come in contact with the tower at various places?

We are a gas processing company in a maintenance shutdown and I am looking for a standard on when we should be removing people from large vertical vessels when there is a lightning storm in the area. The vessels should be well grounded but our electrical engineer cannot confirm that the vessels are well grounded. What do you recommend as a practice?

What safety precautions must go into canceling a show on a stage at an outdoor theme park?

I am the QA/QC (E&I) Coordinator on a major gas gathering project in Nigeria. On our site we have a 120m tall telecommunications tower with several micrwave dishes, to my knowledge the minimum acceptable protection would be 2 air terminals linked together at the top of the tower with 2 down conductors running down opposite legs. Better still would be 4 air terminals with a down conductor for each leg. The subcontractor has installed a single air terminal with a single down conductor which he says is adequate. I am concerned that this will not provide adequate protection and a possible strike could hit the unprotected side of the tower causing damage to the telecommunications equipment.

Is lightning protection required for metal bleachers located at a high school football stadium? There are size tall lighting standards, three per each side of the stadium that are 80’ high. There is a press box on one set of the bleachers and the top of it is +/- 33’ above finish grade.

The question of whether lightning protection is ""required"" or not depends on local option. The lightning protection Standard is a building code, and would be subject to adoption by the ""local authority having jurisdiction."" Since lightning protection is a separate Standard, not a part of the Life Safety Code or the National Electrical Code, it would have to be specifically identified, and in most jurisdictions it is not. It is the reference source if someone chooses the option of providing lightning protection for a structure. In the case of metallic bleachers, it is normally appropriate if you choose protection to provide lightning attachment points above and around the bleachers, and then ground the bleachers. Zones of protection are defined in the Standards based on a 150 ft. radius sphere model. For example, when you place a 150 ft. radius arc tangent with the top of a protected light standard, and tangent with the ground - the area under the arc is considered protected from lightning strikes. Any area breaking this arc is still subject to a direct strike. Therefore, it makes a difference what the relative heights of objects, their proximity, and their total extension away from a protected body may be. You may find that by protecting the light standards and the press box, you have created a protected zone inclusive of the bleachers. Or, you may need to add additional protected light standards (or equivalent protected masts) to provide full protection. There are stadiums with seating areas so extensive that it becomes impossible to provide protection from this ""mast-style"" configuration. In those instances, an overhead ground conductor, similar to the protection provided over power transmission lines, run between the masts over the bleacher area may provide a more inclusive protected area. Obviously this is something that needs to be reviewed and designed to meet the site conditions. We do not have that engineering capability in this office. You may wish to contact one of our member companies for a design and price structure on the necessary system components for protection.

What options are available to me to provide lightning protection to a parking lot?

We are installing a power plant and have a cluster of 7 stacks within a distance of 30m. Is it necessary to install lightning arrestors on all the stacks or will installation on one stack be sufficient?

We have an open football stadium project which is constructing a new steel structure immediately adjacent to an old steel structure. There are expansion joints on walkways and electrical power safety is provided through grounding conductors in all branch circuits and feeders. My concern is lightning. The contractor is thinking of using the steel columns as the down conductor (exothermic welds across all bolted joints). The new structure is much higher (extension of the seating bowl) and the lightning protection system is only provided on the new structure roof. Is there a requirement or recommendation to tie the old structure to the new? There are several places (approx. 60-ft apart) where columns from both structures are within six feet of each other. The bottom 20 feet of the old steel structure has been concrete-encased to increase structural integrity, so any connection would take place approximately 40 feet above grade. What are your thoughts on this system?

When and if a lightning attachment occurs to the new construction, the steel will instantaneously be raised to a potential of maybe 1 million volts, while the adjacent steel section would be at 0 volts. This is the problem with not connecting everything together. Obviously, with that potential difference there would be current flow if anything or anyone bridged that gap, whether it’s 6 ft. of air or an expansion joint. You can also calculate a sideflashing distance for lightning through free air (or building materials for that matter) based on NFPA 780 - par. 4.21.2.4, to see whether lightning will leap the 6 ft. to the existing structure anyway. Using the structural steel rather than down lead cables makes sense. If you used conductor wires, you couldn’t isolate them from the steel anyways, and a steel structural framework provides many more paths to split the lightning into smaller percentages which in turn lowers the ""jumping"" potential. Bonding sections together at whatever level makes sense for potential equalization. Think of it as a ""bird on a wire"" or power line leg, as long as it’s on one wire the potential rises and falls at the same time to no effect. The lightning protection Standards call for lightning protection systems to be bonded to all building grounded systems, including the structural framework, near the top and bottom of the building. On extremely tall structures these systems are interconnected at 200 ft. minimum intermediate intervals. You don’t have the classic building construction in your example, but interconnection at various height intervals is a good idea. By the way, concrete piers and footings around steel columns creates a pretty good grounding medium, since the concrete will retain moisture and may have pretty good electrolytic contact with the surrounding soil.

PERSONAL SAFETY / OUTDOORS / TREES

Is lightning or sheet lightning dangerous at an outdoor activity?

How can I protect my employees in an outdoor working environment, and how can I calculate the earth ohms for the lightning protection system?

Have there been any studies on lightning protection predictors and warning systems, and are they accurate?

Is there any information on the topic of buoys in a body of water?

What do we do if we are out camping in a tent and a storm comes in? Are we safe in the tent, or do we get out and move to a safe place?

Tents are subjects with a lot of variables. If it is prominent to the surrounding countryside, it is subject to a direct strike like anything else. If it is at some low point - the base of a cliff or somewhere in a forest - then it is not likely to be hit directly. If lightning strikes an overhanging tree to your tent, then it may follow down the tree and may or may not jump to the tent or tent frame depending on the conductivity of the materials of the tent. You should be greatly concerned when camping by the step-potential problem from a lightning strike in the vicinity. When lightning strikes it spreads out along the surface of the earth until it equalizes potential (dissipates). The worse the electrolytic content of the soil, the farther this ""electrified field"" may extend from the strike point. You may be standing, sitting, or laying on this ""electric grid"" for a short period. When standing there would typically be a difference of potential between your two feet, depending on how far they are spread apart, causing a current to flow in your body. Sometimes this has little effect and sometimes people get knocked off their feet. Keeping your feet close together is a good practice if you are caught out in a storm. The ""electrified grid"" scenario may be worse if you are lying on the ground. The human body is an excellent conductor, and many of our automatic functions, like breathing or a heartbeat, are controlled by our nervous system, which is a type of electrical system itself. Step voltage from lightning could potentially disrupt your body's normal functioning. This is why when someone is injured from a strike you must take immediate action, like CPR, instead of being afraid that they somehow remain ""energized"". It may be better to be in a tent than standing up taller than the tent in the open, but I can think of few other advantages from being in the tent. It is much safer to seek shelter in an enclosed vehicle, with metal surrounding you and your feet not touching the ground. Of course a structure with a lightning protection system would be even better.

I live in a very bushy area where there are lots of tall native trees. Many children catch the school bus to go to school and then home. They walk between home and bus stops (about 500m distance) through paths with lots of tall trees. It would be greatly appreciated if you could advise that in case of lightning strike what the children should do.

Will lightning travel backwards from its strike, up an embankment and then seek out the biggest tree or would the current hit the tree and follow the root system to the house?

It is difficult to determine what has actually occurred. Wherever lightning strikes – to a tree, a house, the Empire State Building - it will eventually find a pathway to ground. When lightning reaches the earth's surface, it will generally radiate out in every direction seeking to equalize its charge. But that is based on a ""good"" and balanced electrolytic content to the soil. In a case where lots of rocky or sandy or generally poor soil for grounding exists, lightning may travel some distance looking for a preferable ground path or grounding medium. In your example, we cannot distinguish whether the lightning might have struck the tree and headed into the basement looking for a water pipe system or other preferable ground path. On the other hand lightning could have attached to the house, followed a grounded system down through the house, and exited out to the tree root system in more fertile soil. We're not sure that up or down in ground level elevation is as critical as where the best grounding exists. There would normally be some evidence on the tree - damaged bark or a split limb or trunk - if the lightning attached to the tree. There may be damage to insulating materials on the roof or walls of the house if it was the strike point, however, lightning could strike a metallic soil vent or other roof mounted metallic vent and proceed into the basement without leaving much of a trail above ground. A complete lightning protection system can provide several advantages. It provides strike points if lightning is going to attach to your building. It provides a good grounding system and interconnects all building grounded systems to prevent side flashing. It will not stop lightning from striking nearby trees, but it may help with possible side effects. You can protect trees with their own lightning protection system.

When I was 15 years old I was struck by lightning going over a bridge. I read somewhere over the years (I am 32 now) that you are more likely to get hit by lightning the second time around. Is this true? And if it is, can you please tell me why?

Is there any guidance on how far people who are outdoors should be from a lightning storm?

If you go to the NOAA website (http://www.noaa.gov/lightning) they have a lot of good information on personal safety near or during lightning events from an unbiased authority. We normally tell people to ascertain the distance of an approaching storm by seeing the lightning and counting seconds until you hear the thunder. The difference between the speed of light and the speed of sound is roughly 5 seconds per mile, so if you can view and hear these thing you can tell how many miles away the storm is. There are two complications to this. You may not be able to see from your particular vantage point, or the storm approaching on 40 mph winds (.6 miles per minute) may overtake your position quickly, or both. Most experts will say you need to be seeking shelter when the lightning is within 8 to 10 miles, because the lightning you can see may not be the frontal edge of the storm and lightning doesn’t just strike straight down. Sometimes it reaches out horizontally or diagonally before finding a suitable attachment point. In densely populated areas, forests, or rough terrain it is better practice to seek shelter if you see any lightning or hear any thunder. If you are looking at it from a facilities standpoint, or a worker safety situation, it is certainly dependent on your available view of approaching storms, the operating hazard involved, and your ability to track incoming storms. Military facilities which produce and handle explosive materials will generally shut down and seek shelter from storms within a 25 mile radius. There is monitoring equipment for on-site installation, as well as tracking equipment that can be purchased to make a determination (professional golf tournaments do their own computerized tracking), or you may be able to partner with the local National Weather Service office for accurate tracking and monitoring information. Distance for shutting down an operation is best determined by the availability of suitable shelter, and the time involved in shutting down the process. From an ownership standpoint, we have been told that the true value of an in-house storm monitoring system is not just the appropriate warning to shut down, but also the ability to get started up again at the earliest possible time after the hazard has passed.

We will be publicly bidding the installation of lightning protection at a number of our picnic shelters. Will this make the shelters ""lightning-safe shelters"" during lightning storms? One issue is the protection of the structures from lightning damage, but the other issue is whether the industry (LPI) considers an open-sided picnic shelter a lightning shelter or just a rain shelter?

RESIDENTIAL BUILDINGS

Why does lightning prefer to strike sharp edges?

Do metal buildings need lightning protection? If so, does it differ from wood or masonry structures?

If I live in an aluminum-sided house, what impact does that have on lightning safety? I have a pole-mounted anemometer on my roof. Is this a likely target for lightning?

The fact you have aluminum siding has little impact on the likelihood of a strike to your residence. Obviously metal is a better conductor than most building materials, which are insulators, but the attractive effect is minimal for isolated metal bodies. Metal siding generally isn't grounded, like your electrical system, your water piping system, or the structural steel framing on some buildings. Grounded systems, if they are elevated above the roof line, are very good strike points for lightning, but siding, flashings, copings or guttering of metal don't have the same ground path, and aren't much more attractive than non-metallic items. Things that come to a point like roof peaks, ridges, chimney corners, etc. easily release ions, whether they are metallic or not, which makes them valid strike points for lightning. This brings us to your anemometer mast. It meets all the requirements for an improved lightning strike point. It is taller than the surrounding area, made of metal, comes to a relative point, and is grounded. Now it depends on how it is ""grounded"" to determine if it acts as it's own lightning rod or not. If it is only grounded back inside to the equipment or electrical system, you may be bringing lightning back into the house. If it is grounded using only a small electrical ground conductor, it may work once and then the wire could vaporize. If the outside ground conductor comes in close proximity with any other building grounded system, even through a wall, that isn't interconnected with the ground conductor, the lightning could side-flash into the other system. Even if this device functions as a ""good"" lightning strike point and conductor, it only protects about 2 to 1, so if it is 10 ft. above the roof line it protects an area of around 20 ft. radius from it's base. Any part of the house outside this area is subject to a direct strike, according to the lightning protection Standards.

Should the bare copper cable of a lightning protection system be run through the building and attached directly to the wood framing?

If you have a wood door, which is a poor conductor of electricity and you stand behind it without touching it, is it any more dangerous than standing behind a wall in the house?

Is this referring to a specific kind or door like a metal door, or possibly this safety measure is for open doorways instead of doors?

Is this referring to only open windows?

Does lightning pass through closed windows? If so, how often?

Aren’t most houses grounded? If the pipes that leave the house go underground then why is this dangerous? Assuming most houses have plastic piping these days which is a lower conductor of electricity than the older copper or metal pipes.

Do I need a grounding system connected to a weathervane?

I’m interested in information on a residential home. My home is 130 ft. long, has three galvanized steel roofs and about 2500 sq. ft. of flat roofing. I am interested in knowing whether my home can also be protected by the installation of air terminals in trees located at each end of the home, which are higher than the roof? If trees can provide a cone of coverage for the house, will such a system protect my home as well as a system installed on the roof chimney?

I am interested in protection for a 40 ft. stainless chimney above a house on a flat point of land on Lake Ontario that has absolutely no vegetation other than grass for several hundred meters in all directions. What would you recommend?

We have copper strips along the seams of our roof. Does that offer protection of any sort by distributing the electrical current of a lightning strike? We also have a newly installed roof. What is the minimum lightning protection system that will not affect this roof e.g., attachments to one or two chimneys that sit above the roofline?

I own a historic country Inn in Ontario, Canada that was built in 1881. Unfortunately it was hit by lightning and burned to the ground in 1891, then rebuilt as an exact copy of the original. How often does a strike result in fire? I see quite a bit of information regarding other lightning damage but I can’t find anything on fire damage.

I currently have lightning protection installed on my house. Earlier this year, our lightning rods were struck by lightning. Should I have a contractor inspect the system? The rods are brass and one of the rods appears to be white in color and the point is blunt.

Why is it that I don’t often see lightning protection on single-family residential properties?

I’m interested in installing a lightning protection system on my home. Can you advise me what type of system I need and how I can install one?

My home was hit by lightning and most of the appliances and electronics were affected. What can I do to make sure the house is safe short of tearing open all the walls to check the wiring? I had several receptacles, switches, and lamps blown out. I can’t find any information on what to do next. Please help!

RISK OF DAMAGE / STATISTICS

Specifically what criteria should a building owner apply to assess the potential risks associated with lightning?

What factors should someone consider when deciding whether to install lightning protection for new construction? When is it appropriate and not appropriate to install lightning protection with new construction? What are some of the factors that you would look for when deciding whether lightning protection is appropriate for a customer?

How can I tell if protection is necessary in my particular location and who in the area could give me help installing a certified system?

Do all commercial buildings need lightning protection? Do we need to treat steel framed buildings the same way that we treat concrete framed buildings?

Does LPI have a risk assessment form for calculating lightning risk, and if so, why?

How effective are lightning rods? If I have a lightning rod system installed on my home can lightning still damage my home?

Are there any statistics that show a home struck by lightning is more likely to be struck a second time?

How many people have lightning related injuries per year?

Why are there more deaths and injuries as a result of lightning in the United States since 1959?

I am not sure exactly what your questions are. If you are asking why more people are injured today than in the past, then one of the reasons is there are more people and more leisure time than ever before. When people play games outdoors, they have a tendency to try to ""take one more turn"" prior to the storm getting there, which is not a good philosophy. You can post warnings and try to educate people, but they have to make the decision to seek shelter. On the other hand, a lot of lightning injuries from early last century were to individuals who worked outdoors. For example, in the agriculture industry, an individual sitting atop a vehicle like a tractor or combine was exposed at the highest point making them the best available strike point and subject to the most danger. In farming today, along with construction and other heavy industries, many of these vehicles have enclosed metallic cabs surrounding the workmen acting to provide an alternative strike point and a positive level of protection. This has generally lowered the number of incidents for those workers. If you are talking loss of property, then the fact that property values are much higher than 50 years ago is a big factor. Along with that, the addition of many electronically controlled items into everyday life, which are more easily damaged by overvoltages caused by lightning, has increased losses. As more and more buildings, including residences, are wired for not only electricity but also telephone and television antenna service, more lightning is brought into the facility and more potential for damage exists. The National Electrical Code (NEC or NFPA 70), used by most entities as a building code, allows the use of surge suppression devices as an option, but does not require them. This is probably due to the fact that different areas of the U.S. vary greatly in lightning activity, and it isn't felt to be necessary to require these devices in some northern states, as it probably should be in areas like Florida where there are tremendously high levels of lightning activity.

How do clouds generate enough electricity for lightning? What is the average voltage and amperage for lightning?

SURGE SUPPRESSION

What is the difference between lightning and surge arrestors, and is there any link between them?

If a house has surge protection at the electrical panel, telephone line, and satellite receiver, why is a lightning rod protection system needed? Doesn't this protect the house?

How can I improve on surge protection?

Are Gas Discharge Tubes used in home lightning protection?

A gas tube or gas discharge tube is a component of a transient voltage surge suppression (TVSS) device. Most TVSS products are a combination of a couple of different devices. A metal oxide varistor (MOV) or silicone avalanche diode is another component. The MOV reacts very quickly to an overvoltage or surge condition, clamping the line and routing excess voltage to ground and away from the power line. But it cannot handle a lot of excess voltage for very long - it burns itself out. A gas tube on the other hand, can handle more surge but doesn't react quite a quickly. That's why many TVSS units are a combination of both products, so they can react quickly and have a reasonable lifetime, whether they take many small surges or one very large one. TVSS products are available for mounting to the panel board at the electric service entrance, and generally should be installed by a professional like an electrician. TVSS products serve the purpose of ""riding"" the line during normal operating conditions, and clamping overvoltages to ground. The fact that these products must be designed to allow for normal power fluctuations in any utility’s system means that they can't be designed to clamp too tightly or they just end up burning themselves out. The main panel products are sized to protect against fire that could be caused in wiring systems, motors, or appliances. They can't be designed to properly protect the entrance panel and at the same time protect all the low voltage electronic equipment in a building. So you will need an arrestor or TVSS product at the panel, and hard-wired or plug-in TVSS devices (sized for the individual circuit) to protect electronic or low-voltage equipment. Remember all these items have a life-time, they burn themselves out protecting, so if you can get product with pilot lights or some other indicators to show when they are no longer useful that helps with maintenance issues. By the way, all entrances need to be protected - phone, cable TV, or antenna lead-in to do the job right, and these only protect against remote lightning entrance - not the direct strike.

I live on a farm and am plagued by lightning induced destruction of numerous electronic devices including: 1.) Control unit for irrigation system (twice in last 3 weeks-surge comes in via CAT5 wires connecting control valves to main control unit), .2) House alarm system (twice in last month, main circuit board replaced), 3.) Vehicle entry gate controller (circuit board replaced twice). None of the damage was caused by direct lightning strikes but rather appears to be caused by nearby strikes that either create excess static electricity in atmosphere or that runs through ground. I have made sure all systems are well grounded and the contractor for each system assures me that the AC transformers have surge protectors. Accordingly, it appears I need protection other than the AC since all damage appears to have come through non-AC routes. Can you help?

There are various things you may be able to try, but from this distance it is difficult to assist with your specific problems. You can view a listing of our member companies in your area here on our website by clicking on the ""Dealer/Contractor Locator"" on our homepage. There are various advantages from a complete lightning protection system that are not just direct strike protection. The interconnection of all grounded building systems and the implementation of a ""good"" grounding system for the lightning protection will lower the potential problems. Many problems associated with lightning damage are bonding and grounding problems, where the lightning feeds back into equipment along separately grounded lines at differing time intervals. This lack of common grounding causes current to be generated within the equipment which can lead to damage. You are correct in your assessment of lightning traveling through the ground. Regardless of where it strikes, it will travel the earth’s surface to neutralize the charge imbalance. The poorer the soil conditions, the farther it is likely to travel or the more likely it is to seek good grounds like driven rods or water lines and feed back into structural systems. It will also induce excess voltage into active lines running underground, and in your case you have several low voltage systems that are being impacted. Obviously, equipment designed to operate at low voltages is more susceptible to damage from excess voltage. Surge suppression designed for all lines entering a structure provides not only overvoltage protection, but a common ground point for all systems to that device which may alleviate some of your problems. Placing control wiring in metallic conduit and grounding it at both ends may lower the impact of ground charge attaching to the wiring. You should probably consult with a local lightning protection professional or an electrical engineer who can properly review your particular site needs.

I would like to know the difference between Spark Gap and Gas Discharge Tube base arrestors used for line protection. Which is superior?

Should lightning arrestors be put in hazardous areas like a refinery?

TYPES OF SYSTEMS

What are the standards/ requirements for providing lightning protection for buildings?

What are the different systems of lightning protection? What systems are approved by the NFPA, UL, and LPI?

Can you tell me if lightning protection for a commercial building is required per the National Electrical Code?

Do you recommend ESE systems? Are you familiar with an electronically driven ESE system, and can you give me any information on this system specifically, or of this type of system generally? They make some pretty exciting claims, yet they have not been listed by UL or labeled by FM nor approved by NFPA. Do you have an approval process for non-conventional lightning protection systems? Do you have any other information on these things?Is there a device that creates an invisible dome over a building to protect it from lightning?

The product that you have indicated falls into a category marketed as ""early streamer emission"" lightning protection. These products have never been accepted by any national Standards making body in the United States, including NFPA, LPI, or Underwriters’ Laboratories, Inc. NFPA commissioned two separate studies of the ESE device claims in the early 90’s, the first by the National Institute of Science and Technology (NIST) in Washington DC, and a second by an independent group of professional educators called the Bryan Report. In both cases they could find no independent reproducible evidence to support the advertised claims of extended protective area from these devices. NFPA on both occassions refused the ESE product manufacturers request for a Standard covering those products as a specific system. There was a lawsuit brought by ESE proponents over 10 years ago against NFPA, LPI, and some of our member organizations as a ""restraint of trade"" issue. During this process, many witnesses (including worldwide experts) were deposed regarding the actions of these organizations and the functioning of the ESE concept as a viable system substitute. The findings of the court (linked below) were that the ESE producers were the ones with questionable practices, and they were ordered to stop advertising the extended level of protection. This lawsuit is currently in the final stages of determining damages to the defendants, and may be moving toward appeal. Click here for more information. It is not likely that this or any other nationally recognized organization would approve these products as a stand-alone system today. In addition, the IEC (International Electrotechnical Committee) TC Panel 81, which is developing a Standard for international lightning protection installations, has not recognized the ESE devices as a system alternative, even though they have included several designs from various member country Standards. This does not say that the products themselves wouldn’t be valid substitutes for an individual strike termination device or air terminal as described in the Standards. LPI is in the lightning safety business. Any system proven by a national standards process like NFPA would be considered by our membership.

Are there certain industry standards for protection of commercial and/or industrial facilities? Are there objective studies on different methods of protection, i.e. umbrella type versus multiple masts type? Are there other methods beside the two mentioned above?

I have an existing project where we are installing a new substation within a hospital with its own ground grid. The hospital has an existing ""lightning preventer"" on the roof that has its own down conductor to a remote independent ground grid. My question is - shouldn’t that lightning preventer system be grounded (or bonded) back to the main electrical service ground similar to any lightning rod system?

A ""lightning preventer"" is a non-Standard lightning protection system design. In fact, this technology has been rejected by NFPA for document development on at least 3 occassions to my knowledge. There are significant questions about the ""extended zone of protection"" purportedly advertised by these product providers within the scientific community both in the U.S. and abroad. The fact that there is no approved Standard for these systems, leaves us with only manufacturer supported design information. There may or may not be any mention or treatment of bonding interconnections, surge protection, connections to building steel, multiple downleads to split charge, etc. as is required for systems meeting the U.S. national Standards for lightning protection installations. Since there is no lightning protection Standard for these products compliance, then I would suppose you are left to make an educated guess. The 2005 edition of NEC (NFPA 70) requires the interconnection of all grounded systems in or on a structure, and that would seem appropriate to this application. There is a personnel safety issue when you have independently grounded systems for anyone who might be between these systems or working on a piece of equipment connected to multiple isolated systems. Our problem is always that if lightning attaches to any device on a structure, it will seek the ""best"" path to ground. If there are piping or wiring systems within a structure that read better ground than the lightning protection system grounds, then the lightning will leave the system and seek this better path with potentially disastrous consequences since these systems are not designed to handle lightning. The lightning protection Standards call for potential equalization to assure no better ground path than the direct routing of the lightning protection system down conductors. This normally includes bonding the structural steel and building grounded systems to the lightning protection at the top and bottom of each structure.This doesn’t even consider the problem of magnetic flux, which occurs when you try to put lightning voltage on 1 or 2 conductors, rather than multiple conductors at 100 ft. intervals around a building perimeter as in the Standard system. This may cause induced surges to load-side lines within a structure that can effect connected equipment and users. As you can obviously see, this organization doesn’t really believe in the concept of the ""lightning preventer."" In my opinion, there are significant problems with the system design beyond whether it can attract lightning from a large radius, one of which you have pointed out in your question.

With reference to the method of the lightning protection system using early streamer (PULSAR), is it necessary or not to bond all metallic parts (e.g. Mechanical chillers) to the down conductor of this early streamer. In case of long distance between the chillers and the early streamer down conductor, is it permitted to connect these chillers to the reinforcement bars of the roof slab, knowing that the early streamer down conductor is also cad welded to the reinforcement bars of the same roof slab?

I am interested in lightning protection for voice/data systems utilizing fiber optics to isolate the communication lines. I have not seen or read anything on this website that discusses this issue. Could you shed some light on this subject?

I’m curious as to whether your organization endorses the ""Passive-Point Discharge Brush System"" utilized by Lightning Experts. Do you have any information that would be valuable during my consideration of this product?

VEHICLES / TRANSPORTATION

What are the specific dangers of driving a car during a lightning storm?

I have a propane-powered vehicle, and am wondering if it would still be a safe place in a storm? I thought maybe the lightning could cause the tank to explode?

Is being struck by lightning in a car safe because of the rubber tires? And if so, would the tires protect a bicyclist?

I am interested to know about lightning protection of aircrafts and airplanes etc. Since these flying engines do not have grounding systems to earth, what happens when they are struck by lightning in the air?

Is it unsafe to be out on the water in a speedboat or sailboat?

I am trying to find out the design requirements for trolleys and lightning protection. Do you have any ideas on where I might be able to find this information?

We are not familiar enough with your particular trolley application, or trolleys in general to give any truly valuable advice, and we don’t know any specific source for such information. Lightning protection generally works in this fashion - strike termination devices are mounted at prominent locations over the nonmetallic surfaces of a structure to place it within their ""zone of protection."" These strike termination devices are interconnected by conductors, which provide a minimum of two paths to ground from each. Metal construction materials 3/16"" thick or more can be substituted for strike termination devices or conductors. If metallic grounded systems enter a structure, they are interconnected with the lightning protection grounding. If energized lines enter the structure, they are interconnected to the common ground system using surge suppression devices. These are the basics for any protection design against lightning. Now here is our problem - people call lots of different things trolleys. At Disney World there is a trolley, which is a vehicle on rails pulled by a horse. In Kansas City, a trolley is an open tourist vehicle that runs on the street on tires. Some people call the ""cable-cars"" in San Francisco trolleys, and we are not truly familiar with the function of their power system. All these items may need to be looked at specifically, but in general if you surround people with a metallic roof, metallic framing on the sides, and either have a metallic connection (metal wheels) with a rail or no connection to ground (rubber tires) - the people are relatively safe. The lightning should stay on the exterior surface of the metallic structure and jump off to ground. The people who are not in contact with the ground (earth) are not as viable an alternative path. If the vehicle is not metallic, then this metallic system must be replicated - as in the lightning protection system detailed above or by the addition of metallic appurtenances that serve the same purpose. With no designed path suitable to carry the lightning, it may flash through and about the vehicle searching for it’s best path to ground with possibly harmful consequences. We hope this helps a little.

I spend most of my time in the summer in one of the most dangerous areas for lightning strikes (high in the Colorado Rockies). My favorite activity is taking my Toyota Landcruiser four-wheeling. It seems that lightning is present everyday. My vehicle has a full roll cage but no top or doors. I am working on a top that is steel and will operate as a convertible hard top but it’s taking quite a bit of engineering. If I can take your best ideas to my fabricator I will have him build it for me. Any referrals would help too if their are some areas that you feel someone else might better be able to answer.

1.)""My vehicle has a full roll cage but no top or door."" Good, the roll cage provides a ""zone of protection"" for whatever is inside to keep lightning from directly attaching to your head. 2.)""I am working on a top that is steel and will operate as a convertible hard top but it’s taking quite a bit of engineering. Do the doors, side, and rear part of the cab need to be steel to potentially protect me?"" You need to create metallic paths from the roof or roll bar structure to near grade (the chassis) so lightning can follow an exterior metal structure and jump off to ground. 3/16"" thick metal will not burn through when lightning attaches, but it takes less thickness to serve as a conductor (if you don’t care about burnt pinholes on your roof). More metal paths are merrier! 3.)""How is it that glass doesn’t seem to diminish the safety of a vehicle in a lightning storm?"" Because most glass is in a metal frame, the lightning follows the framing and not the glass. A window in a house with a wooden frame can get shattered quite easily. 4.)""Many vehicles have a huge piece of glass in their sunroof and yet I have never heard arguments against having sunroofs for lightning protection."" Anything nonmetallic can be super-heated if lightning must follow that material - it will either burn or explode, depending on the structure and intensity of the attachment. 5.)""As far as windows do I need glass also or will something like lexan plastic windows give me similar protection?"" You don’t get any protection from glass or lexan, it just blows up differently. 6.)""Do you hear of others in open aired jeeps getting struck by lightning?"" Some random vehicles are struck every year. Maybe nothing happens, maybe the electronics get scrambled, and maybe the tires blow. It depends on various factors - type of vehicle construction, intensity of strike, conductive capability of earth below, etc. 7.)""Most jeeps and Landcruiser FJ-40’s are all-fiberglass tops in hard top form."" Let me make this clear - there is no non-metallic that conducts or stops lightning from attaching - it burns or blows up! We have seen fiberglass antennas that look like a cornstalk after it’s been through a combine from a lightning hit - at least the part that was recoverable. 8.)""If I made my top out of fiberglass and had a steel edge around the entire vehicle would that help or do I need a certain amount of wire mesh and how thick, inside the fiberglass top hidden behind the headliner?"" Fiberglass may keep the rain out and it may never rust, but it serves no purpose in lightning safety. If you worry about lightning, use metal - solid or mesh - and tie it all together electrically. It will create a shield to help protect what’s inside.

I have a 35 ft. mobile tower that I move on a daily basis. The tower is an anodized aluminum structure consisting of 5 ""U"" shaped (10"" x 2"" x 7’) sections approximately 1/4 - 3/8"" thick. The trailer is a metal structure with outrigger arms that come into contact with the earth. I am concerned about operator safety and my approach for operator protection is to bond all of the equipment to the trailer including the mast and then provide a braided copper cable and grounding rod to ground the structure. Is this sufficient?

NFPA 780 states that metallic bodies 3/16"" thick or thicker may be substituted for strike termination devices, and lightning conductor (in lieu of cables). A 3/16"" thick metal will accept a lightning attachment without burn-through. The problem with burn-through is it may break the moisture seal for a structure, causing future problems with moisture. If you have an open tower frame that is prominent, the potential for moisture problems may not be an issue, so the use of lighter section materials may be satisfactory. It normally takes somewhat less metal to transfer the lightning from an attachment point to a grounding system, since metallic structures that are electrically interconnected and continuous will allow the lightning to split along multiple paths - there is normally enough free available electrons in a tower structure to transfer the lightning and no other proximate systems or structures for the lightning to jump to as an alternative path.If the tower is electrically continuous with a metallic trailer frame (or bonded to it), the lightning seeking the best path to ground will use the framework as conductor. Driving a single ground rod bonded to the framework may be sufficient, although NFPA 780 calls for a minimum of two grounds for a lightning protection system on any structure. Metal support pedestals for the trailer that are electrically continuous with the trailer frame and earth may not be as effective as a driven ground, but do provide alternative paths for the lightning to reach earth ground and can help serve the splitting function. Beyond this direct strike protection for the structure, personnel protection will require that all systems are grounded in common to equalize potential, so all systems and the structural frame raise and lower together as the voltgage changes. This can be accomplished by a single point ground method as you have mentioned. Personnel on the trailer would then be similar to a ""bird on a wire,"" where changes to voltage have no effect. If personnel are expected to stand on the ground (earth) and be in contact with trailer-mounted devices or the framework, this could be a problem since they could provide another alternative ground path. This last scenario could be addressed by providing a metallic work platform for individuals to stand upon that is electrically continuous with the trailer framework.

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