Chaps, The grounding of a shield room has always been a tricky subject. In the US we have the NEC code that basically want's everything connected, which contradicts some EMC requirements. The Shield room hence needs some tricks:
1) One of the functions of the outer skin is to terminate impinging fields. Current is generated on the shield surface that will flow across joints and seams ( and hence leak into the chamber ) unless it's routed somewhere.... Earth. 2) While buildings usually have a good earth, they typically have a noisy earth. The last thing we need is building noise on our room, so an earth dedicated to the chamber is provided. 3) To stop building noise from using the shield room earth, all metallic connections are cut, and plastic used instead. This is where the NEC folks can get upset. Their concern is that the two grounds could lift with respect to each other.... I've never seen that happen, and I've gone looking for it. So that I can sleep at night, I ensure that an operator can't touch metal referenced to the different grounds at any one time. 4) Power supplied to the room has to be directly connected. To stop building noise from entering the room through this wiring, the noise is removed to the case of a filter. I've located my filters very close to the room single point room earth connection, so the noise can get there easily without crossing one of my room seams or joints. 5) Any equipment I use with the room is referenced to the room ground. Power for this equipment is filtered at the same point the room power is. Most instrumentation used in EMC is quiet.... so they don't supply much noise. I don't believe there is guess work involved with room grounding. The above is based on conversations with many room installers. I suggest that if you have specific questions, contact the folks that made yours. --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
