size of equipment ground conductor

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curt swartz said:
If you add an additional 100 amp circuit to the pull box later you will pull a correctly size EGC with the new 100 amp conductors. I don't see any reason to increase the EGC for circuits that don't exist.
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They stopped all 40 of the #10 ground wires in 40 MC Cables in the junction box before they got back to the PDU.
Then he mounted a Ground Bar in the J-Box and pulled (1) #10 Ground wire from the J-box to the Pdu.
40 hots, 40 Neutrals and 1-#10 ground go from the J-Box to the PDU.

There is only (1) #10 Ground Wire from the PDU to the J-Box.

Which is exactly my point.

If they did the same routine for an added 100 Amp Feeder just like they did for all the rest. they would stop the #8 Ground wire in the J-Box also, then the single #10 they have going from the Ground Bar in the j-box to the PDU is now not large enough.

That's exactly my point.
 
I have always been taught that you can derate the EGC 1 size. But I have never seen where in the code it states that it is ok.
But every electrician I have worked with does it. So in the OP's case, you could run a #12 ground?
 
Aleman said:
I have always been taught that you can derate the EGC 1 size. But I have never seen where in the code it states that it is ok.
But every electrician I have worked with does it. So in the OP's case, you could run a #12 ground?
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You cannot downsize the equipment grounding conductor. Many ec's downsize their neutral or grounded conductor on services and that can be okay esp for residential work but you cannot downsize the equipment grounding conductor.

In fact if you upsize your conductors for voltage drop or whatever reason then the equipment grounding conductor must be upsized proportionately.
 
I wonder where that came from. From what I have seen the practice is not uncommon. My guess is that it is confusion
between an ECG and other grounded conductors. I have seen a few contractors derate the grounds on motor wiring for example.
How about the service to a industrial control panel or a piece of equipment or machine?
 
I see that a #10 ECG is good for up to 60A. At least that's what I got from looking around. 250.122 2008 is what I was looking at.
So now I'm a bit cornfused. Because you can't run 10awg conductors for a 60 amp circuit. Am I looking at the wrong info?
 
Aleman said:
I see that a #10 ECG is good for up to 60A. At least that's what I got from looking around. 250.122 2008 is what I was looking at.
So now I'm a bit cornfused. Because you can't run 10awg conductors for a 60 amp circuit. Am I looking at the wrong info?
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Table 250.122 is based on the size of the overcurrent protective device. If you have a 60 amp breaker generally you will have a #6 conductors run however the equipment grounding conductor only needs to be sized to #10. From 70 to 100 amps the equipment grounding conductor needs to be #8 but again the circuit conductors must be sized by 310.15 tables.

Only in sizes 14, 12, &10 is the equipment grounding conductor the same size as the circuit conductors
 
Aleman said:
I see that a #10 ECG is good for up to 60A. At least that's what I got from looking around. 250.122 2008 is what I was looking at.
So now I'm a bit cornfused. Because you can't run 10awg conductors for a 60 amp circuit. Am I looking at the wrong info?
Click to expand...

no, you aren't. the OCPD determines the EGC size.

and while it's not the EGC, the size of wire you ground a service with can be quite a bit smaller
than the service entrance conductors.... a 3/0 will do any size service, for example.

and voltage drop has to be considered with EGC size, as well... and it can turn into a real
pain to comply with.
 
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