Full Size G

[LarryFine]

Apparently, the bottom line is that each EGC be sized as if it is the only one for the entire parallel set.

 

[jumper]

Apparently, the bottom line is that each EGC be sized as if it is the only one for the entire parallel set.

Yep. The size of the OCPD is for the entire set of a phase(s) and the EGC is also.

There have been proposals, Don G and others, to eliminate 250.122 and just use the same format as 250.66 and 250.102, basing the EGC on the size of a set of ungrounded conductors,and not the OCPD, just like the GEC and bonding jumpers.

 

[infinity]

Apparently, the bottom line is that each EGC be sized as if it is the only one for the entire parallel set.

Yes, you could have parallel sets in a single raceway where you would only install one EGC. For example in the aforementioned 2500 amp installation if you use a single raceway like a wireway you could have 10 sets of 250 kcmil and one 350 kcmil EGC.

 

[qcroanoke]

Anyone know of any situation where you would have (3) #350 with a #350 ground? The same size ground is the question.

I have seen that required on UPS installations.
Made no sense but mfgr. required it so we did it.

 

[steve66]

I have seen that required on UPS installations.
Made no sense but mfgr. required it so we did it.

It's also a very common spec. for feeders to medical equipment.

 

[kwired]

In what installation would "but in no case shall they be required to be larger than the circuit conductors supplying the equipment." apply except for parallel conductors? Feeder taps might be one case, but that is already addressed in 250.122(G).
I can't think of any. If the CMP intended it to apply to the parallel sets of conductors they should have worded it like Note 1 to table 250.102(C).

I run into this with motor circuits a lot - where the OCPD can be higher setting then conductor ampacity.

I've had instances of motors supplied by 12 AWG conductor on a 40 amp breaker. Table requires 10 AWG EGC - but since ungrounded conductors are only 12 AWG EGC doesn't need to be any larger.