Equipment Grounding Conductor

[infinity]

What about these two examples with all 75 degree C terminations:

Ex. 1) 100 CB, w/ #3 THHN ungrounded conductors (100 amps), #8 EGC = OK

Ex. 2) 100 CB, w/ #2 THHN ungrounded in 52 deg C ambient (130 * .76 = 98.9 amps, next size up 100 amps), #8 EGC = OK

In the second scenario there is no increase in the ungrounded conductor size because a #3 THHN with that temperature correction would not be large enough in the first place. (110 * .76 = 83.6 amps)

Since the ungrounded conductor did not increase in size 250.122(B) would not apply.

 

[charlie b]

Ex. 2) 100 CB, w/ #2 THHN ungrounded in 52 deg C ambient (130 * .76 = 98.9 amps, next size up 100 amps), #8 EGC = OK

Rob I agree with this viewpoint (presuming, of course, that the calculated load is not higher than 98.9 amps, say for example 99.2 amps). But it has been a matter of some debate here before. My greatest criticism of this whole topic is that the NEC does not declare, "increased in size FROM WHAT?"

In your second example, some will argue that you if start with a 95 amp load, and on that basis alone could have used a #3, but then you put it in a 52C environment, so that now the #3 is not big enough anymore, then when you pick the #2, the ungrounded conductor has been "increased in size" FROM #3 to #2. I think you "sized the conductor," and that you did not "biggie size the conductor." I seem to recall holding the minority opinion here.

 

[infinity]

Rob I agree with this viewpoint (presuming, of course, that the calculated load is not higher than 98.9 amps, say for example 99.2 amps). But it has been a matter of some debate here before. My greatest criticism of this whole topic is that the NEC does not declare, "increased in size FROM WHAT?"

In your second example, some will argue that you if start with a 95 amp load, and on that basis alone could have used a #3, but then you put it in a 52C environment, so that now the #3 is not big enough anymore, then when you pick the #2, the ungrounded conductor has been "increased in size" FROM #3 to #2. I think you "sized the conductor," and that you did not "biggie size the conductor." I seem to recall holding the minority opinion here.

This thought process originated with one of your past posts. I agree with you that the "increased from what" aspect of this article is ambiguous. With the exception of VD conductor increases, which seem to be more clearly defined( replace a smaller conductor with a larger one), examples can be thrown about to prove that increases in ungrounded conductor size do not necessarily trigger an automatic increase in the size of the EGC. I'll remain with you in the minority.