Lightning Arrestors

Suppose your building has a lightning protection system installed per NFPA 780 and LPI-175. You've also got a staged surge arrestor system protecting your building's power distribution system. You've bonded all the metallic objects, thus eliminating differences of potential.

So, all of your equipment is safe, right?

No, because you left out something. Your antennas are unprotected, and through those a surge can be injected into the very systems you spent all that money to protect. This is why you need antenna protection.

A gas tube arrester actually absorbs much of the energy that passes through it, rather than simply diverting the energy and letting it possibly circulate.

This arrestor is a sealed tube that contains an inert gas. The surge jumps across the electrodes, through this gas. The spacing of those electrodes is what determines the voltage level of the gas arrestor. This device offers high reliability, repeatability, and power stabilization.

You'll notice the part numbers, such as "LA-5100." As you have probably guessed, the "LA" stands for "Lightning Arrestor." They all have that, but the number part is different. What does it mean?

The number denotes the frequency the particular arrestor will dampen.

The two main standards for lightning protection are:

• NFPA 780, Standard for the Installation of Lightning Protection Systems.
• LPI-175, Standard of Practice for the Design-Installation-Inspection of Lightning Protection Systems.

Why don't these include requirements for lightning arrestors on antennas? Because these standards address the requirements for the structure. It's a matter of scope. They don't require you to install MOVs on the input side of your 120V equipment power supplies either, but that's also a part of a good overall plan for lightning protection.

Another thing you should do is ensure you don't have separate grounds between systems. That creates a difference of potential, which can result in flashover or lethal shock. The shield of the coax in your antenna system needs to be bonded, at some point, to the same plane as the power supply to the equipment. At your service point, ensure the various systems are bonded together. Driving separate ground rods doesn't accomplish this; the earth has far more resistance than a run of #4 copper wire does. If you do have separate ground rods, bond them together using wire and clamps listed for the purpose.