Douglas Krantz - Technical Writer - Describing How It Works

Should the Lightning Rod be Grounded Separately from the Electrical Ground?

By Douglas Krantz | Residential

Should the Lightning Rod be Grounded Separately from the Electrical Ground?

Should the Lightning Rod be Grounded Separately from the Electrical Ground?

Greetings Douglas,

I am looking for some advice here. I was told that I was NOT supposed to connect my lightning rod to the grounding rods in place for my permanent power. But your article made it seem like I AM supposed to.

I have a lightning rod (rebar) and a copper wire connected to a grounding rod. 6ft away or so I have two grounding rods connected to my electrical power for that building. From your article it seems like this is a problem. What would you recommend exactly?

Thank You, JL

It sounds like I'm being picky, but there are two separate electrical systems in your cabin: the utility power system, and the lightning rod protection system.

Utility Power Electrical System

The utility power system includes things like the plumbing and metal air ducts HVAC for the cabin. If your toaster, for instance, falls into a sink full of dishwater, rather than making your plumbing system electrically charged, the power circuit for the toaster will short out; the circuit breaker then turns off the electricity.

For all intents and purposes, the utility power, along with anything metal which can conduct electricity, is a single electrical system. This is the system that has two ground rods (two rods to provide better connection), separated by 6 feet (1.88 meters). The separation is required because, if they're closer to each other, at least electrically, they are really just one ground rod.

If lightning strikes the power-pole in the back of the cabin, the current from the lightning bolt is routed safely to the dual grounding rods.

Lightning Protection Electrical System

The lightning rod on the roof protection system for the cabin routes the current from a lightning-bolt around the cabin and its internal electrical and grounding system. Rather than the lightning-bolt current running through the utility power electrical system, the lightning rod, its very heavy gauge wire, and its own ground rod is the route the lightning-bolt current takes.

Keeping the Systems Separated, or Keeping the Systems Connected Together

You were told by someone that the two systems are supposed to be separated. To keep the systems separated, each one has to have their own ground rods, and the two systems can't be electrically connected together. This is a good way of keeping the two systems separated.

Separated Systems: Lightning jumps air-gaps. If the voltage is high enough, like between clouds in the sky, lightning can jump through the air for miles or kilometers. In the case of your cabin, though, where two systems are close together, the potential lightning voltage is a lot lower. It's reasonable to assume that the lightning won't jump a full six feet (1.88 meters).

Remember, the wood walls mean nothing to lightning: if the bolt of lightning requires it: the lightning will just go through the wood wall. For lightning, the distance between metal building's electrical system and the metal of the lightning rod system is important. Even with an outside wooden wall separation between the two systems, the 6 foot clearance needs to be kept.

You have two choices when installing lightning rods on top of your cabin: separated or together.

The first choice is to totally separate the two electrical systems: the utility power system with the plumbing and HVAC, and the lightning protection system. This is the suggestion where you don't connect the lightning rod on the roof to the dual ground rods.

The second choice is to connect the two electrical systems together. Because of the lead-in wires for an outside TV antenna or satellite dish, the only separation between the two electrical systems is your TV set and any other connected electronics you have in the cabin.

Lightning can easily jump that small gap.

Bottom line about outside TV antennas satellite dish antennas is that they are effectively lightning rods. They are connected to the internal utility power system for the house as soon as they have a "lead-in wire" to the electronics. Think of that lead-in wire or cable, and the especially the electronics that it's connected to, as a fuse.

If the TV antenna or satellite dish electrical system is grounded separately from the cabin's utility electrical system, when lightning strikes the TV antenna or satellite dish, the current from the lightning will burn out the fuse-lead-in wire, along with the fuse-electronics, and possibly cause a fire.

With an outside TV antenna or satellite dish, the lead-in wire connects the two electrical systems together, so in that case, connect the ground rods for the two grounding systems together using very heavy gauge wire.

Separate or Together

If there is not an outside TV antenna or satellite dish, separating the lightning rod electrical system, with its grounding rod, from the cabin's internal electrical system, with its dual grounding rods, makes sense.

If there is an outside antenna or satellite dish, combining the lightning rod electrical system with the cabin's internal electrical system, with its dual grounding rods, makes sense.

Douglas Krantz
Life Safety
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