Yes this is definitely a homework problem. I cannot find table '250.122(C" anywhere in my textbook. I did find a spot where it said that on 15,20, and 30A you must use the same size ground as conductor. So I'm guessing I could undersize the ground for the 40A circuit if I had the table and thats the size I would need. I would guess that I would only need one ground for all 3 of these circuits.
Yes this is definitely a homework problem. I cannot find table '250.122(C" anywhere in my textbook. I did find a spot where it said that on 15,20, and 30A you must use the same size ground as conductor. So I'm guessing I could undersize the ground for the 40A circuit if I had the table and thats the size I would need. I would guess that I would only need one ground for all 3 of these circuits.
That is not true. The size of the Equipment Grounding Conductor (i.e., the minimum allowable size) is based on the rating of the overcurrent protection device (OCPD). NEC Table 250.122 lists various OCPD ratings and gives the minimum EGC size. For 15 amp, the size is #14; for 20 amp it is #12, and for 30 amp it is #10. These values are for copper conductors; aluminum conductors must be larger.I did find a spot where it said that on 15,20, and 30A you must use the same size ground as conductor.
That is correct, but it would be better not to guess. The text of paragraph 250.122(C) tells you exactly that. It also says that the size must be based on the largest OCPD protecting any of the circuits in the same conduit.I would guess that I would only need one ground for all 3 of these circuits.
That would be a bad guess. If you have a 15, a 20, and a 40 in the same conduit, you can use a single EGC, if you size that EGC for the 40 amp circuit.So I'm guessing I could undersize the ground for the 40A circuit if I had the table and that?s the size I would need.
Yes this is definitely a homework problem. I cannot find table '250.122(C" anywhere in my textbook. I did find a spot where it said that on 15,20, and 30A you must use the same size ground as conductor.
That is not true. The size of the Equipment Grounding Conductor (i.e., the minimum allowable size) is based on the rating of the overcurrent protection device (OCPD). NEC Table 250.122 lists various OCPD ratings and gives the minimum EGC size. For 15 amp, the size is #14; for 20 amp it is #12, and for 30 amp it is #10.
It does not have to be the same size. It just can't (generally) be smaller. The (nobody ever does this but it is legal anyway) exception is that if the ungrounded conductor is aluminum, and if the EGC is copper, then the EGC can indeed be smaller than the ungrounded conductor.Actually it is true that for 15,20 and 30 amp circuits the EGC is the same size as the phase conductors.
Oh, c'mon, make Charlie happy and say "same ampacity."I should have stated at least the same size. :smile:
That wouldn't make me happy, Larry. EGC sizes are not selected on the basis of the ampacity of the EGC conductor. :wink:Oh, c'mon, make Charlie happy and say "same ampacity."