Letter Re: Faraday Cage Grounding

Sunday, Dec 11, 2005

Mr. Rawles,
I have been enjoying reading your excellent blog. Some thoughts for you on the post from Rourke and the troubles presented by EMP.

The only circuit breaker that could possibly open before an EMP surge could do damage are some large (400+ pounds) industrial types and they start at about $40,000. Be quite the installation. Any breaker you can get for less than that just ain't nearly fast enough.

You want to be a bit careful about installing a grounding system in your house that isn't connected to the house's grounding system, if it has one. The National Electrical Code forbids it, and for good reason.

Let's say I build a Faraday cage in my basement, and drive a ground rod just for it. Now let's say that my home is grounded--most are. If the physical arrangement of my cage is such that I can touch the cage and something else metallic in my basement, such as a washer, dryer, freezer or some such because there are now two separate ground pathways there can be a voltage difference between the two and since I'm touching both I become the conductor for any voltage differences. Does that make sense?

Grounding systems for some large installations can be huge and very complex, but they are all, electrically one system so no voltage differences can exist.
Hope this helps. - Catshooter

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