Re: Server Room Grounding
AudioCableGuy, the place to start is your isolation/stepdown transformer. You first want to make sure the Xo is properly grounded to the nearest building electrode. The nearest electrode would be in the following order. Building steel, water pipe, or a cable ran to the service electrode. Once that is complete you have a base to start from.
From there you go as elaborate as you want. A popular method is to use a raised floor grid constructed of # 6 AWG bare copper conductors constructed of a grid of course as the name implies. I design them so the cables runs underneath each equipment line-up. Then from each equipment rack you connect it to the grid with a # 6 AWG. The grid should be bonded to every steel building column, ac panel ground bus, water pipe, conduit, cable rack, ect, and most importantly the Xo of the transformer(s) supplying the equipment. The purpose of the grid is not necessarily to lower the impedance to earth, but rather than lower the high frequency impedance between equipment racks and the transformer.
Don’t get hung up on too large of sizes of grounding conductors. They will not lower the high frequency impedance. A 6 AWG exhibits about the same impedance as a 750 MCM at frequencies higher than 10Khz. All that is needed is one large enough to handle the likely fault current imposed on it at DC or 60Hz
You mentioned TVSS grounding. There are no special requirements for grounding these devices. I do not suggest using a grid or any other ground structure such as a signal ground for TVSS grounding. Most disturbances are in the differential mode and ground is not involved except at the service entrance. Just use a service entrance class C device with L-N modes only, and then use class B devices with all mode protection at the sub-panels and transformers.
Hope that helps DERECK
