NEC 110.10 Excluding L-L-G Faults?

[meofleur]

Anyone aware of any issues with NEC 110.10. Why does it say you only need to consider L-L, 3-phase, or L-G faults when considering equipment short-circuit ratings? The L-L-G fault can be the worst case in some situations. Any light anyone can shed on whether L-L-G faults are omitted by mistake or on purpose would be great...

 

[charlie b]

My guess is that it is an unintended omission. Perhaps you could submit a proposed change for the 2011 NEC? All you would need for substantiation is a sample calculation that shows a double-line-to-ground being more restrictive than any of the others.

Welcome to the forum.

 

[LarryFine]

Isn't an L-L-G fault simply two simultaneous L-G faults?

Or would it be more accurate to say it's really a L-L fault?

There should be no neutral current if the faults are balanced. :wink:

 

[charlie b]

Actually, Larry, the L-L-G fault is a separate case from either the L-L or the L-G. It is analyzed on its own, using similar techniques as the other two, but with different results.