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Ground fault / Separately derived systems

Ground fault / Separately derived systems

Ground fault / Separately derived systems

(OP)
Greetings,

                         I have a Topaz Line noise Ultra Isolator 15KVA 208Y/120 in,                          208Y/120
                         output supplying our computer center.  Some of the UPS's and surge
                         protectors are indicating a ground fault condition.  We are reading a
                         voltage of 16 volts across the neutral and the equipment ground.                          This 16
                         volts are from some phase imballance and some electronic injection I                          am
                         sure.  If we install a jumper wire between the neutral and equipment
                         grounding bus the fault condition lights go out and the voltage drops                          to .0
                         levels.
                         My question, is it acceptable to bond the equipment grounding bus                          and
                         the neutral bus together in the breaker panel that is served from the
                         isolation transformer?
                         This gets back to the question of connecting the equipment ground                          and
                         the neutral buss bars together at other than the service entrance                           panel.
                         I am of the opinion that the isolation transformer is a separately                         derived
                         system and is permissable to bond the equipment ground and the                          neutral
                         busses together being as how it is the first panel to be served from                          the
                         "new system".  Am I interpreting this right and is this the intent of the
                         NEC?  If not then what should I do to clear the fault condition?
                         SGC

RE: Ground fault / Separately derived systems

Not only is this acceptable, but requried by 250.30(A)(1).  This is assuming that there is not a bond between the grounded and grounding conductors at the output of the UPS, as this bond is only permitted at one location.
Don

RE: Ground fault / Separately derived systems

It is perfectly acceptable and logical to bond the N and the ground bus (in the equipment)noting that the N at the transformer is further grounded somewhere on the plant/building main earth/ground

RE: Ground fault / Separately derived systems

(OP)
Thank you resqcapt19 & RajT for the timely and informative responce.
This is my first visit to Eng-Tips and I can see I have tapped into a wealth of knowledge that I certainly will be viewing and using.
Keep up the good work!
SGC

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