[Myrddin]

Thanks. That is what I wanted to know. You are saying that earth is not good for EMP sheilding. Why ground a faraday cage to earth then?

A Faraday shield is often wrapped around a sensitive electronics facility for lightning protect. Lightning is a natural EMP. The Faraday cage keeps the high frequency EMP off the electronics gear and the lightning bolt is shunted to ground. A big copper container can build up a static charge relative to other objects. Recall how a Van de Graaff generator is constructed? The ground shunts the build up.

[Revel]

Thanks. So the earth is not a good conductor of Magnetism and the EMP will just pass through it. But a copper cage will have a voltage induced in it and said voltage will be disapated to ground(shunted). Does that sound right.