Monday, March 21, 2005

Toward a Provisional Philosophy of Grounding

About grounding. There's so much information and advice out there that is sometimes contradictory. Partly this is what it means to be a radio amateur. Some folks have some credentials, but it's hard to know how to interpret what you read.

My background is in Physics, Radioastronomy, EE, and IT. So I have some textbook knowledge of electricity & magnetism and some practical experience with radio telescope systems. I would not claim to know much about lightning protection, but I know enough to be skeptical.

The basic problem is that few if any hams are able to test their grounding systems. Some people survive some dramatic "events", and their equipment sometimes does and does not. But in most cases there's no statistical significance. The commercial tower people probably know a lot, but they don't try to integrate RF systems into their residences. A few hams in high-risk locations survive multiple strikes every year. They're the ones to listen to.

There are some general principals that can guide us. Mainly, you want to provide a low impedance path to ground from "up high" that will not pass through you, your house, or your equipment. In a residential environment, there are always compromises. The ideal ham shack would be a windowless metal building on its own pad with a carefully laid out grounding grid and protection on every wire coming in and out. (Like a cell phone hut.) Failing that, it is probably a good idea to have as many ground rods out there covering as much territory as possible. If you don't "bond" your ham ground to your AC ground (and other lightning protection grounds, if any), you run the risk that there will be high potential differences between them during an event. What would happen if your AC plugs (all 3 wires) suddenly were at 20 kV relative to your equipment?

My local SPG system is an attempt to establish a locally bonded system that will forestall large potentials from occuring between anything near my ham gear. I will try to connect it to the AC entrance ground and a new ground rod system, difficult as that is on a granite ledge.

I don't have confidence (in a statistical sense) that this will work against the likely threats. It was fun to build. At least, it will improve the RF and AC safety grounding by a bit.

Read below to see the project at my QTH.

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