[TCML] comments on designing a lightning protection system

["Jon Busack" <boo1062@xxxxxxxxx>]

Please have a professional do your lightning protection system design and
installation. It's more complicated than it seems.

That cabling is designed especially for lighting, and for good reason.

Lightning amperage is so high it actually "water hammers" your conductors.
In plumbing if your pipe has a 90-degree bend, the pressure-surge of water
hammers the bend as it turns the corner. In the same way, when lightning
current hits a corner in the conductor it can blow out from sheer force of
the current and the EM fields.

No sharp bends in the cable. Point your T-splices "downstream" so the cable
bends in the way the current wants to go. There are rules about what kind of
cable mounting to use and how far apart.

Ground rods- some rules here also- at least two, no less than 6 feet apart,
depends on soil conductivity. Use an underground "ground ring" that you
splice your downfeeders to. In the ground ring use copper 400kcmil minimum,
and best to use thermal connections like cadweld. Consider a ground rod at
each downfeeder.

Ground the lightning protection system to your service entrance. Make sure
your building has a single service ground that all your grounding conductors
feed back to. There are risks involved with multiple building grounds
although intuitively it seems right. Especially with lightning strikes, if
you have multiple grounds you can have a ground surge pass under the
building and one side of your building might be several thousand volts
higher than the other side as the surge rolls through.

There are also design rules like the "rolling sphere" which tell you how far
apart to put the rods, and how high, depending on the topology of your
towers and buildings and nearby trees.

Don't do this one yourself.

Some  suppliers will actually design a system for you if you use their
products.

Here's a supplier with a good reputation-- http://www.harger.com/
Also check out NFPA 780 as Bert recommended. It has complete design
recommendations, drawings, diagrams.
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