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Joined: Jan 2004
Posts: 615
Jps1006 Offline OP
When is lightning protection on a building required? Is it installed strictly as customer preference or engineer recommendation, or can an AHJ tell you to put it in? If the AHJ does tell you to install it, what code would set the standard for when a structure meets the criteria to now require it?

NFPA 780 appears to tell you everything about how to install it when required, but doesn't look like it specifies who needs it and who doesn't.

Does one of the IRC or IBC cover that?

Joined: Mar 2005
Posts: 1,213
Basic lightning protection is covered in standard building techniques- a properly bonded and grounded structure is inherently lightning resistant from a lightning rod standpoint.

As far as lightning rods and lightning arrestors go, IBC is completely silent on this matter. NEC Article 280 and 285 aren't much help either, but then, NEC is a safety codes and not a design guides. It does surprise me that NFPA 780 is silent! The greatest risk from a lightning strike is one that comes from the power lines, and is generally provided for by surge arrestors on the utility's side. (If the strike were to occur at the pole in front of a house, it's going to overwhelm the surge arrestor anyhow.)

It doesn't really apply to you, but DoD Tech Manual 5-684 requires lightning arrestors when transitioning from aerial to underground conductors, and to protect aerial transformers; I think this may be based on NESC requirements, but I'm not sure. Beyond that, it's an engineering decision on whether it's cost justified. I do not believe it's ever outright required past the service. But a TVSS on the main switchboard/panel (and at every key distribution point in an article 708-type facility) is always a good idea.

Joined: Mar 2005
Posts: 1,213
The degree to which lightning protection is required, is a subjective decision requiring an examination of the relative criticalness of the structure location and its contents to the overall mission of the facility. Those structures containing elements vital to the operational mission such as air traffic control towers, radar installations, navigational aids, and communications enters are examples of facilities which obviously must be protected. However, every building or structure does not require that a lightning protection system be Installed. For example, buildings primarily used for the storage of nonflammable materials do not have a critical need for protection. Three of the factors to consider in ascertaining whether a given structure should have a lightning protection system installed or in determining the relative comprehensiveness of the system are the relative threat of being struck by lightning, the type of construction, and the nature of the facility.

3.8.1 Strike Likelihood.
The relative likelihood of a particular structure being struck by lightning is a function of the keraunic level, i.e., the thunderstorm activity of the locality, the effective height of the structure and its attractive area. Average thunderstorm activity can be determined from the isokeraunic maps shown in Figures 3-2 and 3-3. Then using the techniques described in Section 3.4, estimate the frequency with which strikes to the structure may occur. Use this estimation as one of the inputs to the decision process.

3.8.2 Type of Construction.
Steel frame buildings with metal outer coverings offer the greatest inherent protection against lightning damage. Steel towers also exhibit a high immunity to structural damage. Additional protection for these type buildings will probably be required only for very critical facilities in highly exposed locations. Steel frame buildings with nonconductive, but nonflammable, outer coverings (like brick or other masonry) also offer a high degree of protection against lightning damage. The greatest hazard is posed by pieces of masonry being dislodged by stroke currents passing through the outer coverings to reach the structural steel underneath. Minimal protection consisting of interconnected air terminals to down conductors and steel support columns will be sufficient to prevent this type of structural damage. Buildings constructed of nonconductive materials such as wood, concrete blocks, or synthetic materials are the most susceptible to destructive damage. A complete auxiliary protection system will be required to prevent lightning damage to buildings utilizing this type of construction.

If a strike to the facility poses a threat to human life, either to the occupants of the structure or to those persons whose safety is dependent upon reliable performance of the equipment and people inside the structure, comprehensive lightning protection should be definitely provided even in areas of low thunderstorm activity. At the other extreme, the need for the protection of buildings used primarily to store nonflammable or nonexplosive items is doubtful unless the stored items are critical to system operation, the building is usually exposed, etc. In between these extremes are those structures whose incapacitation would cause an inconvenience or present other difficulties short of life-and-death situations. With these structures, a careful analysis must be made to determine the relative likelihood of outages from lightning in comparison to normal equipment failures, downtime for maintenance, and other outine occurrences. Though not directly related to the protection of electrical or electronic installations, Reference 3-10 is recommended for further guidance in performing the tradeoff analyses to determine the degree of lightning protection required for specific facilities.

The Lightning Protection Code, NFPA No. 78, issued by the National Fire Protection Association (3-9) contains the basic requirements for the minimization of personnel hazards in the event of a lightning strike to the structure.

The requirements of NFPA No. 78, however, are not sufficient to protect the electrical distribution system, signal and control cables, or sensitive electronic equipment from surges produced by either direct or indirect strokes. Thus additional steps such as providing lightning arresters on power lines and on outside signal and control cables, providing counterpoise cables for overhead and underground cables, providing comprehensive electromagnetic shielding on sensitive cables, and installing fast response surge protection devices on circuits exposed to lightning discharges should be taken. MIL-STD-188-124A refers.

Hope this helps!

Joined: Apr 2003
Posts: 139
Here in Florida, lightning protection is only required for three occupancy types as indicated in the Florida Building Code.

Anything beyond that is per design consideration based on risk analysis and protection needs.

Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter
Joined: Jan 2005
Posts: 5,460
Likes: 3
Cat Servant
Thank you, Steve, for an excellent response. I always wondered why so many churches had lightning rods on the steeple, over the altar! laugh

Joined: Apr 2003
Posts: 139
Believe it or not, churches are among the most "struck" buildings in the US.

Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter
Joined: Jul 2004
Posts: 9,955
Likes: 34
Must be that big "air terminal" on top of the steeple. wink

In Florida toll booths are way up on the list too. I never thought of it until we built MM99 on I-75 but that is the highest thing for miles around ... until they put in the radio tower.

Greg Fretwell

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