Hello. Let's say there is a instrument needed to be EM wave-shielded in High voltage discharge lab. Building Faraday cage becomes necessary and the instrument is moved to inside the cage. The cage is grounded to lab ground and the frame ground of the instrument (it is also signal ground for the instrument here) is connected to metal piece of the cage. We suspected that EM wave from gas discharge makes noise which can flow along a ground wire. (so also Faraday cage I think) In this sense, EM wave still disrupts shielded instrument inside the cage via ground connection. Could you tell me that my reasoning is right? If so, is it typical case in EMI environment and how can I removes ground noise to the instrument? It may need to be noted that our lab is 2nd floors and total length of wire from lab ground to earth is to be very long thus huge ground potential rise with respect to earth in transient time (~discharge time) is expected.