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Chimney with lightning rodOutdoor Lightning Protection System Designs

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Basic design specifications for lightning protection systems:

This lightning protection system article describes common Outdoor Lightning Protection System Design Specifications & Details using aluminum components - lightning protection systems, certification, installation, and lightning protection system inspection.

We provide information about lightning strikes, lightning hazards, related equipment, sources of lightning protection system installers, and lightning strike risk assessment. Page top photo courtesy of Bud Schoch, PE.



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Design Details for Outdoor Lightning Protection Systems Using Aluminum Components

Photographs of lightning protection system components

Example Lightning Protection System Installation Details for Outdoor Systems

[The photographs of details of an old lightning protection system shown here were NOT the work of any of the companies or sources described at this website.]

[Click to enlarge any image]


Example Lighting Protection System Materials for Outdoor Installations

Photographs of lightning protection system components

[The photographs of details of an old lightning protection system shown here were NOT the work of any of the companies or sources described at this website.]

Question: is it ok to conceal lightning protection system conductors?

Loose loop in the lightning  protection cable at the Valeciana church (C) Daniel Friedman2017/07/10 ian said:

Can lightning conductor tapes be concealed/overboarded?

Reply:

Ian

Yes, under NFPA 780 Standard for the Installation of Lightning Protection Systems, a component of lightning protection systems include "cable conductors" that are used to route the conductor safely over or through the building without damage.

My photo shows the lightning cable conductor on the La Valencia Church in Guanajuato, Mexico.

But you can see that the church tower design includes a corner passage above eye level through which the lightning protection system conductor cable is routed to earth.

Watch out: a danger with concealed cable conductors is that a splice or connection that is not visible might become loose, disconnected or otherwise not reliable. When I took this photo (in 2012) someone had pulled out a loose loop in the lightning protection cable and was using it to secure the end of the bell pull rope. As the grounding electrode for this section of the lightning protection system isn't visible I'm not sure that the hidden end of the cable connects to earth.

More photos of this church lightning protection system are at LIGHTNING PROTECTION, HOW IT WORKS.

Cable conductors are one of the five elements of a protection system (Strike termination device, cable conductor, grounding electrode, bonding of the system to other building metal components, and surge protection for some building electrical devices or systems).

According to NFPA 780, installers are permitted to conceal the UL Standard-96-listed lightning protection system conductors (from below the strike termination device and below the roof) within the building. The supporting lightning strike theory (and experience) is that when a strike occurs, and given properly sized, routed, and connected and grounded conductors, the current flow, though enormous, is so brief that conductor overheating (that would present a risk of fire or building damage) doesn't occur.

Splitting the strike current flow through multiple paths (at least two conductors must be used) also reduces the overheating and fire risk.

The downlead cable ends at a ground rod dedicated to the lightning system (not shared with the electrical system).

Indeed at a lightning struck home I inspected at which the strike current found the building's electrical system ground, and where the electrical system's grounding conductor was bonded to the water pipe at the water meter near the house wall, the strike current melted the water pipe causing a flooded basement!

Experts note that an advantage of running the lightning protection system conductors through the structure during construction (it's more costly to do so as a retrofit) makes it easier to bond other building components to the protection system.

Watch out: The installation details for the lightning protection system conductor are critical. Keep in mind that making a mistake during installation of the lightning protection system may make the risk of building damage or fire greater than if no system were installed at all.

For example adding a strike termination device and conductor that runs through the building but using improper splices along the conductor (that don't conduct the current to earth) might simply conduct the lightning strike current into the building to cause a fire.

In addition to using proper splices, the conductor routing must always run down or horizontally (never "up"), and must be routed without 90 degree or other sharp bends - constrictions that could cause a failure of the conductor splices and fastenings during a strike, or that could cause a failure of the conductor to route the lightning strike current to earth rather than into the structure itself.

Resources on Lightning Protection System Design & Installation

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LIGHTNING PROTECTION SYSTEM DESIGN at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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