Any protection a faraday cage may afford, no matter how big or small, is seriously compromised if a metal conductor passes through it. The conductor can be a power line, communications circuit, or utility pipe or conduit. You will find that any real government hardened building has no metal of any kind passing through or to it. Their communications are fed by strictly fiber opti cables with no shielding.

That also nullifiies the affect of a faraday cage on a metal cased computer due to the power and porting circuits passing through the body.

Do not ask me how I know.