I did not know it was that much. Q: Does the change in max effective length = change in impedance?
Apparently Nema may not know that either. Although they do know the overall impedance is reduced.
From Nema Bulletin 97, 2009
You wouldn't cherry pick your data would you? - Nah
That bulletin doesn't say the phase to ground fault impedance
is reduced. It also says, that a supplemental wire EGC mat or may not reduce impedance for a phase to ground fault. Seems quite inconclusive to me.
So what if supplementing with a wire EGC actually impedes more than without... what say you then?
What it does say as if conclusive, is a supplemental wire EGC has no effect on a phase to
neutral fault. That seems quite a logical deduction to me, without having to use any software. :happyyes:
In any case I think you and $S are on the right track. The trend is going toward "use an internal EGC regardless of raceway".
That's the 'trend' in practice... and it may possibly be detrimental in some cases, going by NEMA's inconclusive statement.
I say we go back to the broad brush of previous editions:
"Any ccc up-size, gets an equal EGC up-size. Exception: Calculate under engineering supervision (TCC diagram showing available fault current)"
Again going back to NEMA's statement, what if upsizing actually impedes trip action???
And to provide exception to calculate under engineering supervision could result in the use of something similar to the Corwin Theory.... :?
Perhaps two proposals: 1) as 'suggested' in post #42, and 2) an exception for use of GEMI analysis.