yes Joe,
i can imagine that, in addition to VD, any form of a 'ground loop' would also be a concern,the issue of overall power quality at hand.... as such we are directed in 647 to 250.30 .....

Quote
(B) Ungrounded Systems.
The equipment of an ungrounded separately derived system shall be grounded as specified in 250.30(B)(1) and (2).
(1) Grounding Electrode Conductor. A grounding electrode conductor, sized in accordance with 250.66 for the derived phase conductors, shall be used to connect the metal enclosures of the derived system to the grounding electrode as specified in 250.30(B)(2). This connection shall be made at any point on the separately derived system from the source to the first system disconnecting means.
In a separately derived system that is ungrounded, a bonding jumper must be installed to connect the disconnect enclosure and equipment grounding conductors to the grounding electrode system.

which now brings up this nifty little ex a tad back in A....
Of course this does not apply, being in A, and having rid the nuetral from the system, yet it is of interest in that 647 may in fact provide for the 'fix' for it......

Quote
Exception No. 1: A bonding jumper at both the source and the first disconnecting means shall be permitted where doing so does not establish a parallel path for the grounded circuit conductor. Where a grounded conductor is used in this manner, it shall not be smaller than the size specified for the bonding jumper but shall not be required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a parallel path.

To add to this little 'code loop' here, pursuant to the 'PQ' angle, we now delve into 'listings'....

Quote
The practice of grounding the secondary of an isolating transformer to a ground rod or running the grounding electrode conductor back to the service ground (usually to reduce electrical noise on data processing systems) is prohibited if an item in (1) or (2) of 250.30(A)(4) is available. However, an isolation transformer that is part of a listed power supply for a data processing room is not required to be grounded in accordance with 250.30(A)(4), but it must be grounded in accordance with the manufacturer's instructions.

somebody here's had to have been there.....
( speak up, don't be shy...)
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[This message has been edited by sparky (edited 07-28-2002).]