Efficient Isolated ground

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moresi

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Wiring a large conference room with some countertop workstations. I am responsible for design and want to provide some isolated ground receptecals at the countertop work areas. Will be installing a new three phase sub panel in this room and am looking for most economical and efficient way to get a proper isolated ground circuit to these receptecals. Plan to serve panel with 4 wire SER cable - not pipe. Any way possible to come off this panel with isolated ground circuit or am I mandated to go back to main service panel. It is a long run and therfor I would like to avoid this. Also piping to this sub panel is really not feasible. Thoughts, suggestions, etc. Should I run Type AC cable from main service panel to receptacles or is there a better method?
Thanks for any help.
 
A true IG system would have the IG conductor go all the way back to the service neutral or the the XO of a transformer feeding the panel. Either way you would be hard pressed to accomplish using SE cable. Depending of the size of the feeder you may be able to use MC cable.

Why are you using an IG system?
 
Rob provided some good advice about the source of IG circuits.

One also needs to be aware that computers that are interconnected with cabling will make the IG circuits useless.
As Rob asked, why the IG circuits for this equipment?
 
Some of these computers are integrated with some sensitive radio communication equipment (public safety) and the installation of some IG recepts. was discussed. I too felt that it really was not achieving anything and if the consensus is that it is in vain then I will omit the IG circuits. I am in agreement that true isolated ground circuits are very tricky to achieve.
 
Why waste your time and the customers money. Why not hire electricians to install a NEC compliant panel with properly installed branch circuits and be done with it.
 
moresi said:
Some of these computers are integrated with some sensitive radio communication equipment (public safety) and the installation of some IG recepts. was discussed. I too felt that it really was not achieving anything and if the consensus is that it is in vain then I will omit the IG circuits. I am in agreement that true isolated ground circuits are very tricky to achieve.
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Generally long isolated grounds serve no purpose when it comes to RF blocking, since RF can localize resonate in long runs of wire, proper shielding, and local ferrite core choking and filtering would seem a much preferred path to take, as well as RF blocking any networking and or other inter-connecting cables.

Triplett and other manufactures make some great SPDs that include RF blocking, as well as all mode filtering, and with line conditioners so voltage fluctuations will not be a problem either.

I myself am not fond of IG circuits because if the circuits are installed properly as per the NEC, generally theres not a problem, so many are installed that serve no purpose.

but that is just my opinion.
 
I, too, have installed IG circuits, and I agree that it's a useless gesture in a properly-wired system.
 
And on the large systems I have seen/tested the vast majority were either not installed properly or compromised at a later date.
 
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