Does the use of ground fault detection change the performance requirements for equipment grounding conductors?
This came up in the question about voltage drop in the EGC in long feeders.
One of the things that confused me was the change between the 2002 and the 2005 code. In the 2002 code there was no clear requirement that the ground fault path actually be capable of tripping the breaker. But the requirement to facilitate the operation of the over-current device is now explicit. IMHO this was probably an unintentional omission from the 2002 code, seeing as it was a requirement for ungrounded systems in the event of a double fault.
Soares Chapter 11 provides references for the maximum impedance that can be expected to trip a breaker in the instantaneous trip range. This seems a reasonable criterion for 'facilitating operation'; in the event of a short circuit the breaker would trip at its fastest possible rate. However the code itself doesn't seem to specify what 'facilitating operation' means is useful quantitative terms; Soares suggests that tripping in 1 cycle is 'fast enough', but what about 10 cycles or 1 second?
My question: if the overcurrent device incorporates ground fault detection, does this permit increased impedance in the EGC circuit? With ground fault detection, operation of the breaker would happen at ground faults well below the normal trip rating of the breaker. I am not asking if this would permit smaller EGC conductors than other portions of article 250; but if ground fault detection would assist in meeting the performance requirements of 250.4(A)(5)?
-Jon
