Question about TT systems—are ground detectors used with them? There are two good reasons for ground detection. One is that if a ground occurs somewhere in a normally ungrounded system, nothing happens overcurrent-wise, but then the second fault will likely cause two overcurrent devices to operate simultaneously.
Another consideration is that without some resistive load-to-ground in the ungrounded system, the normal phase-to-ground capacitance can charge up to much greater than line-to-line voltage, and cause severe arcing damage in the insulation. In cases in the US with intentionally ungrounded systems, this has been learned though {expensive} trial-and-error lessons.
A restriction in US ungrounded systems is that phase-to-neutral loads may not be served, as would be conceivable in an ungrounded 4-wire wye system.
[This message has been edited by Bjarney (edited 07-22-2003).]
