60 Degree, 75 Degree, Equipment Grounding Conductor

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1. Is sizing a #10 egc with a #4 phase wire for a 60A circuit from the 60 degree column acceptable? I say yes, but I seem to have run into the next question.
2. Let's say I size #4 for a 60A circuit from the 60 degree column. At the job site, the terminations of the equipment and the conductor installed are 75 degree rated. Would my #4 wires technically be considered upsized and I would need to upsize the ground as well? My #10 egc now appears to be undersized.
3. Does anyone know of a device, not made for residential, that has terminations that are only 60 degree rated?
 

Dennis Alwon

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Where would you find 60C rated wire.... Generally that is TW wire or NM cable. I have not seen it in years. That being the case then your #4 is upsized and you have to upsize the equipment grounding conductor. Now if you are talking hypothetically then you would argue that #6 at 75C is the sufficient so the #4 is upsized again however the code is not clear on that.

60C terminations are not around anymore unless you are tying into some old equipment
 

infinity

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2. Let's say I size #4 for a 60A circuit from the 60 degree column. At the job site, the terminations of the equipment and the conductor installed are 75 degree rated. Would my #4 wires technically be considered upsized and I would need to upsize the ground as well? My #10 egc now appears to be undersized.

IMO the use of the 75 degree C rating of the terminals is part of one of the conditions of 110.14(C)(1)(a) so you're not required to use it. You are only required to comply with one of the four conditions in that section and you would comply with #2.
 

Smart $

Esteemed Member
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Ohio
IMO the use of the 75 degree C rating of the terminals is part of one of the conditions of 110.14(C)(1)(a) so you're not required to use it. You are only required to comply with one of the four conditions in that section and you would comply with #2.
I agree. 100A or marked 1AWG, or less for either, we are not required to use the 75°C size as the minimum size.
 

kwired

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If the topic of discussion is sizing an EGC, 250.122 applies. I don't recall temperature rating being mentioned at all in this section, an EGC is not intended to carry current for long enough duration to impact either of those aspects.
 

Smart $

Esteemed Member
Location
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If the topic of discussion is sizing an EGC, 250.122 applies. I don't recall temperature rating being mentioned at all in this section, an EGC is not intended to carry current for long enough duration to impact either of those aspects.
The topic is sizing the EGC, and compliance with 250.122(B). 110.14(C) applies to the circuit conductors, upon which an upsized condition is based.
 

Carultch

Senior Member
Location
Massachusetts
1. Is sizing a #10 egc with a #4 phase wire for a 60A circuit from the 60 degree column acceptable? I say yes, but I seem to have run into the next question.
2. Let's say I size #4 for a 60A circuit from the 60 degree column. At the job site, the terminations of the equipment and the conductor installed are 75 degree rated. Would my #4 wires technically be considered upsized and I would need to upsize the ground as well? My #10 egc now appears to be undersized.
3. Does anyone know of a device, not made for residential, that has terminations that are only 60 degree rated?

1. The temperature rating of the wire does not apply to the equipment grounding conductor. Whether you use #10 TW, #10 THWN, or #10 THWN-2 for your EGC, it will all have the same grounding performance. This does bring up the question of whether or not it complies to use 90C rated current-carrying wires with a 60C rated EGC, and completely ignore the 60C rating of the EGC. I would think it is, due to the fact that the EGC can be bare and still do its job, while the main reason for the insulation on the EGC is to curtail wire abrasion and wire/conduit corrosion. This is more of an an academic question, because 60C rared wire is rare.

2. Good question. The intent of requiring upsizing the EGC proportionally to the phase conductors is for applications where you have to upsize to curtail voltage drop. The idea is that if your circuit is long enough for this to matter, your grounding conductor needs extra size to reduce the resistance for the length. If you have to upsize for ampacity reasons, NEC2014 does not require you to do this, since your starting point is "the minimum size that has sufficient ampacity for the intended installation".

Per the letter of the NEC, it doesn't state that voltage drop is the only reason why you would have to upsize the EGC. Even if you use larger wire than needed due to it being left over from the previous job, it still requires you to proportionally upsize the EGC. Even if you use larger wire than needed due to ignorance about whether you have 60C or 75C terminations, and you end up with 75C terminations, you'd still need to upsize the EGC.

The loophole on this, is that you can sneak in a 60C rated splice, and make your EGC now correctly sized. First of all...good luck finding one. Second of all, while that makes the system comply, it actually makes it slightly less safe. One more component to add resistance to the main circuit, and potentially fail.

3. Remember: The rule is that the burden of proof is on the one who claims it is compliant at 75C for 100A and less. The default rule is that it is rated for 60C for 100A and less, and 75C for over 100A. Unless listed and marked otherwise. Today, most terminations and equipment are listed and marked otherwise. Even though it is a mostly academic rule, it still requires your due dilligence

Here's an example of a component that has a 60C rated termination. Notice that it is rated for #8 wire, and only indicates 40A per circuit.
http://www.mcmaster.com/#7618k658/=zlxwj1

Also, any time you use ROMEX, even 90C rated ROMEX, you have to comply with 60C rated terminations. 334.80
 
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Per the letter of the NEC, it doesn't state that voltage drop is the only reason why you would have to upsize the EGC. Even if you use larger wire than needed due to it being left over from the previous job, it still requires you to proportionally upsize the EGC. Even if you use larger wire than needed due to ignorance about whether you have 60C or 75C terminations, and you end up with 75C terminations, you'd still need to upsize the EGC.

So, you are saying that a #10 G. is undersized for a #4 phase conductor in just about any commercial application?

I have a commercial application and RFI saying that a #10 G. is undersized for a #4 phase conductor. Technically by code, this should be acceptable per 110.14(C) and table 250.122. But if 75 degree wire is installed every time (assuming there is no commercial equipment rated for 60 degrees only), then I would need to upsize my EGC. And by doing that, I shouldn't actually follow 110.14(C), otherwise, I will have a change order for replacing the EGC in possibly every circuit sized from #8 to #3.

Here's an example of a component that has a 60C rated termination. Notice that it is rated for #8 wire, and only indicates 40A per circuit.
http://www.mcmaster.com/#7618k658/=zlxwj1

Your link says the device is rated for up 221 degree F (105 degree C).

  • kwired
    If the topic of discussion is sizing an EGC, 250.122 applies. I don't recall temperature rating being mentioned at all in this section, an EGC is not intended to carry current for long enough duration to impact either of those aspects.

I agree that the temperature rating has nothing to do with the EGC. That is not one of my concerns. I am only concerned with the temperature ratings of the terminations and phase conductors and if they require an upsized EGC.

Where would you find 60C rated wire.... Generally that is TW wire or NM cable.

I wouldn't. I am more concerned about the possible 60 degree terminations on the equipment.

Sorry for the long post.
 

infinity

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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.
 

Carultch

Senior Member
Location
Massachusetts
Your link says the device is rated for up 221 degree F (105 degree C).


It says that #8 wire is only rated for 40A. And the part isn't physically marked with the temperature rating. The NEC requires your part to be both listed and labeled otherwise, to take credit for the 75C rating.
 

Carultch

Senior Member
Location
Massachusetts
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.

What if you assume terminations are 60C rated out of ignorance, run #4 Cu wire, even though terminations end up being marked otherwise for 75C on both sides? Does that count as "an increase in size"?
 
What if you assume terminations are 60C rated out of ignorance, run #4 Cu wire, even though terminations end up being marked otherwise for 75C on both sides? Does that count as "an increase in size"?

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?
 

Smart $

Esteemed Member
Location
Ohio
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.
...and it doesn't matter if all terminations and wire insulation temperatures are rated greater than 60°C.
 

Smart $

Esteemed Member
Location
Ohio
What if you assume terminations are 60C rated out of ignorance, run #4 Cu wire, even though terminations end up being marked otherwise for 75C on both sides? Does that count as "an increase in size"?

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.
110.14(C)(1)(a) does not require you to use the 75°C column to size conductors where 75°C or greater rated conductors are used. Refer to 110.14(C)(1)(a)(2).

This is both the literal and safety standpoint because it is compliant... period.

During a bolted ground fault, the smaller the EGC, the longer it will take for an overcurrent device to trip. The too small point is where the ocpd does not trip.
 

Carultch

Senior Member
Location
Massachusetts
...and it doesn't matter if all terminations and wire insulation temperatures are rated greater than 60°C.

So what you are saying, is that in an example such as this, all of the following are compliant installations:
1. #6 wire, #10 ground, 75C terminations and 90C wire
2. #4 wire, #10 ground, 60C terminations and 90C wire
3. #4 wire, #10 ground, 75C terminations and 90C wire

Am I correct?
 

infinity

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So what you are saying, is that in an example such as this, all of the following are compliant installations:
1. #6 wire, #10 ground, 75C terminations and 90C wire
2. #4 wire, #10 ground, 60C terminations and 90C wire
3. #4 wire, #10 ground, 75C terminations and 90C wire

Am I correct?

Yes, even though #3 in your list could make it appear that the #10 is too small you are not required to us the 75 degree C value for the #4 conductors.
 

Smart $

Esteemed Member
Location
Ohio
So what you are saying, is that in an example such as this, all of the following are compliant installations:
1. #6 wire, #10 ground, 75C terminations and 90C wire
2. #4 wire, #10 ground, 60C terminations and 90C wire
3. #4 wire, #10 ground, 75C terminations and 90C wire

Am I correct?
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).
 
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infinity

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New Jersey
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So what you are saying, is that in an example such as this, all of the following are compliant installations:
1. #6 wire, #10 ground, 75C terminations and 90C wire
2. #4 wire, #10 ground, 60C terminations and 90C wire
3. #4 wire, #10 ground, 75C terminations and 90C wire

Am I correct?

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

Actually at 75° C #6 is rated at 65 amps.
 
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