What I believe Scott35 is describing is a three-phase four-wire delta configuration, but at double the voltage of the usual “240/120V 3ø 4W∆” system. See lower left illustration at 6L6.net/localuser/busbar/imag/eei10.distckt.jpg
It has been used in some cases to skirt the NEC 230-95 service-entrance ground-fault protection mandated for ‘1000+ ampere’ 480Y/277V systems. It is the worst combination for a grounded 480V system, because 277-volt overcurrent devices cannot be safely applied, similar to the problematic corner-grounded 480V-delta system, but it still has the potentially disastrous capability of switchgear arcing-ground-fault burndown recognized {and normally protected for by GFP} in 4-wire 480Y/277V solidly-grounded systems.
{The mutant ‘480/240V 3ø 4W∆’ system is used occasionally by some utilities in the US, but should have 3-element metering to correctly register energy use as in other 4-wire solidly-grounded systems—with careful understanding of limitations.}
[This message has been edited by Bjarney (edited 01-06-2004).]
