Wiring Protection & OCPD

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necnotevenclose

Senior Member
I have always understood that you have to size your ground based on the OCPD but do I have to size the branch circuit conductors based on my OCPD as well?

Example:

47A = 3#8+#6G (75-degC CU) on a 60A breaker?
 
necnotevenclose said:
Example:

47A = 3#8+#6G (75-degC CU) on a 60A breaker?
Click to expand...
What would be wrong with using a 50A CB?
240.6(A)

The EGC would also be a #8 ~ 250.122
 
necnotevenclose said:
I have always understood that you have to size your ground based on the OCPD but do I have to size the branch circuit conductors based on my OCPD as well?

Example:

47A = 3#8+#6G (75-degC CU) on a 60A breaker?
Click to expand...

Why have an equipment ground larger than the phase conductor? :confused: :smile:
 
necnotevenclose said:
I have always understood that you have to size your ground based on the OCPD but do I have to size the branch circuit conductors based on my OCPD as well?

Example:

47A = 3#8+#6G (75-degC CU) on a 60A breaker?
Click to expand...


I think I get what you are saying but correct me if I am wrong. If you have a load of 47 amps then a #8 would be good for 50 amps based on 310.15 75C column. If this is a load that you can potential size the breaker to 250% of 47 amps then the breaker would be a 125 amp breaker. Are you asking if the EGC would have to be based on the 125 amp breaker which would call for a #6?

I don't think you ever have to size the EGC larger than the conductors.
 
Thanks for the reply guys. As a pure example and nothing more, what if this was an existing facility where my calculated load was 47A and I wanted to use an existing 60A CB? Would I be able to utilize 240.4(B)?

My understanding is that in order to provide protection for the circuit (not to cause overheating which could lead to a ground fault potentially causing an arc fault) that I would need to change out the CB to 50A.
 
nyerinfl said:
read 210.3, the answer is yes.
Click to expand...

Art. 250.122(A) states that the EGC shall not be required to be larger than the circuit conductors supplying the equipment. The OP had #8 wire as his circuit conductors with a #6 egc. That is not necessary, however you would have to size the egc at least as large as the circuit conductors if Table 250.122 requires that.
 
Dennis Alwon said:
Art. 250.122(A) states that the EGC shall not be required to be larger than the circuit conductors supplying the equipment. The OP had #8 wire as his circuit conductors with a #6 egc. That is not necessary, however you would have to size the egc at least as large as the circuit conductors if Table 250.122 requires that.
Click to expand...

The question wasn't about the sizing of an EGC.
 
nyerinfl said:
The question wasn't about the sizing of an EGC.
Click to expand...

I realized that however the op stated in his example a #6 EGC with # 8 conductors and I was stating that it was not necessary.

The other part of his question was answered so I responded to what looked like an error. Was I wrong in doing so????
 
nyerinfl said:
No you weren't wrong, I read you quoting me as saying I was wrong, wasn't trying to take a shot at you.
Click to expand...

I see what you mean. I was not clear at all. I quoted you to state that not all of the OP's statement was correct. You said yes-- I was trying to clarify that the whole statement was not totally accurate.

Sorry for the confusion.
 
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