60 Degree, 75 Degree, Equipment Grounding Conductor

[Carultch]

Can't say any are compliant without an OCPD rating!

Assuming 60A OCPD, all could be compliant. #6 requires load to be less than 55A... but it being a potential smallest size conductor IMO in no way limits one from choosing a #4 as the smallest size, i.e. using 240.4(B) is optional; lack of using 240.4(B) cannot be used to penalize one on another requirement.

These are irrelevant when based on 60°C size as permitted in 110.14(C)(1)(a)(2).

I did intend there to be a 60A OCPD, fully utilized at 48A continuous so that 240.4(B) wouldn't apply.

I think I get it. Please correct me if I am wrong.
It is optional to take advantage of 240.4(B)
It is also optional to take advantage of 75C terminals/90C wiring as allowed for exceptions to the defaults in 110.14(C) where applicable.
The value of "the minimum size that has sufficient ampacity for the intended installation" as is used for the starting point of upsizing the EGC wire can be based on conductor size WITH OR WITHOUT the two aforementioned options that can reduce it.

 

[kwired]

If you size the conductor at 60 degrees C according to 110.14(C)(1)(a) then for a 60 amp circuit a #4 would be the correct size without using the next size up rule. Since the #4 hasn't been increased in size then the EGC need only be a #10.

I agree.

That is exactly the question I am trying to get answered. From a literal standpoint, #4 with a #10 G. is acceptable per the NEC. From a safety standpoint, the wire size has been increased from #6 to #4 and requires the ground to be upsized.

A better question, what actually happens during a ground fault when the EGC is sized too small? Does anyone have any real life events as evidence?

Problem you presented is outside the range of possibilities that code making panel may have considered when making this rule IMO, and I don't have an answer for it other then see what your AHJ will allow. I also find this rule to have other occasional conflicts that likely were not intended to require increased EGC size at times, but is hard to write a rule to cover all possible situations without seeming like overkill in some of those situations. Example why can we end up in a situation needing to increase the EGC of a circuit protected at 25 or 30 amps to 8 AWG in some cases yet could have same size ungrounded conductors in the adjacent raceway but on a 60 amp circuit and they only need a 10 AWG EGC?

What happens when the EGC is too small? The return path has more resistance and therefore less fault current flows. Doesn't prevent OCPD from opening, but does make it go further into trip curve before opening because current is lower. But we have same thing with a long run of ungrounded conductor. Take a 20 foot run of 12 AWG and fault it to ground, breaker trips nearly instantly from a human perspective. Take same 12 AWG and fault it at the end of a 200 foot run (and for now assume same nearly zero resistance of a return path) you still have enough resistance to significantly reduce the amount of fault current flowing and most likely you are able to notice it takes at least some amount of time before the breaker opens. Now throw in a 12 AWG as the only possible fault return path and you have doubled the circuit resistance.

Available fault current from the source does also come into play as it is the upper threshold of how much current can possibly flow regardless of other conditions. Small source with high impedance - some of these rules may not matter all that much in some cases or in others may even become even more important, it is going to take time to trip the OCPD on short circuits and ground faults compared to a source with a low impedance. 250.122 is however sort of a one size fits all application, you can provide better protection then the minimum requirements here by selecting overcurrent devices that have trip curves to meet your needs.

 

[Smart $]

I did intend there to be a 60A OCPD, fully utilized at 48A continuous so that 240.4(B) wouldn't apply.

I think I get it. Please correct me if I am wrong.
It is optional to take advantage of 240.4(B)
It is also optional to take advantage of 75C terminals/90C wiring as allowed for exceptions to the defaults in 110.14(C) where applicable.
The value of "the minimum size that has sufficient ampacity for the intended installation" as is used for the starting point of upsizing the EGC wire can be based on conductor size WITH OR WITHOUT the two aforementioned options that can reduce it.

Use of 240.4(B) is optional.

Optional, defaults, exceptions to 110.14(C)(1)(a)??? 110.14(C)(1)(a) is written such that you have to use one of the four conditions listed. It is not optional, but you do have four potential options. And while I know what you mean using the other two words, it is best if we just eliminate them from the discussion.

 

[Smart $]

...It is optional to take advantage of 240.4(B)...

Use of 240.4(B) is optional.
...

I'd like to elaborate on this a little. If at some point on this circuit one actually does take advantage of 240.4(B), which isn't all that uncommon in cases of voltage drop, I would say you cannot use the larger size as the minimum (#4 in our working example) to determine the upsized EGC size. :blink: