Table 310.15(B)(16) & 110.14 (C)

[aelec84]

Hello forum,

Can this be clarified per the scenarios as stated below?

A) If a #3 AWG THWN-2 wire is used to feed loads but terminated on 60C terminations then ampacity of that conductor is only 85A and not 115A. Similarly if its terminated on a 75C termination then its 100A.
B) Does the equipment provision as stated in 110.14(C)(1) is the circuit-breaker?
C) If the equipment is listed for 60C and 75C terminations and #1 AWG THWN is being used for a circuit rated 100A does that mean 250.122 (B) kicks in and needs to be addressed?

Wires not used for ampacity adjustment or correction factors. Thank you.

 

[infinity]

A) Yes
B) It would be the equipment that the circuit breaker is connected to like a panelboard.
C) I think that it could be a argued that they have been increased in size.

 

[david luchini]

C) If the equipment is listed for 60C and 75C terminations and #1 AWG THWN is being used for a circuit rated 100A does that mean 250.122 (B) kicks in and needs to be addressed?

I would say no. 110.14(C)(1)(a) says "shall be used for one of the following."

#1 thwn at the 60deg ampacity is one of the listed options.

 

[jaggedben]

My take:

A) Yes. But it's pretty unlikely these days you'll be landing 3awg on anything that isn't rated for 75C. (Maybe if re-wiring 50+ year old equipment.)
B) It could be the circuit breaker lugs, panelboard main lugs, disconnect lugs. Whatever component the wire actually lands on that is labeled with the temperature rating.
C) Yes (assuming copper, not alumimum), but the final answer to whether the ground would need to be upsized depends on whether any deratings for temperature or current-carrying conductors are required.

 

[jaggedben]

I would say no. 110.14(C)(1)(a) says "shall be used for one of the following."

#1 thwn at the 60deg ampacity is one of the listed options.

I don't think this matters if 2awg meets the requirements for the circuit. 250.122(B) isn't written that way.

 

[aelec84]

I don't think this matters if 2awg meets the requirements for the circuit. 250.122(B) isn't written that way.

I would say no. 110.14(C)(1)(a) says "shall be used for one of the following."

#1 thwn at the 60deg ampacity is one of the listed options.

Does this mean that if #1 THWN-2 is used then its limited to 130Amps but now the ground wire has to be upsized? sorry its confusing.

 

[jaggedben]

Does this mean that if #1 THWN-2 is used then its limited to 130Amps but now the ground wire has to be upsized? sorry its confusing.

Since the ampacity (if correction and adjustment is not required) is 130A, but you stipulated the circuit was only a 100A circuit, then yes. That's 250.122(B) requires. (Dumbest rule in the book, IMHO, but that's what it requires.)

Note again that if you had to adjust the 130A for temperature or current carrying conductors, the ampacity could be less that 130A.

I think what david may be saying is that since the code doesn't say you have to use the 75C ampacity, and since the 60C ampacity of 1awg copper is 110A and of 2awg cu is 95A, if your circuit current requirement were actually between 95A and 100A, then you could say the 1awg is not upsized, because 2awg would be too small. But note that if for example your circuit current requirement is actually 92A, you are allowed to protect that with a 100A breaker per 240.4(B). So then you could use 2awg and 1awg would be upsized.

 

[Dennis Alwon]

Does this mean that if #1 THWN-2 is used then its limited to 130Amps but now the ground wire has to be upsized? sorry its confusing.

To avoid upsizing the egc I would install a fuse disconnect or circuit breaker disconnect at the equipment and use a 125 amp breaker. From the disconnect to the unit use a 100 amp breaker and you are good to good.

 

[wwhitney]

But note that if for example your circuit current requirement is actually 92A, you are allowed to protect that with a 100A breaker per 240.4(B).

Yes, but 240.4(B) is optional. So if you choose not to use 240.4(B), and you choose to use the 60C ampacity, then #1 is the smallest Cu conductor size for a 100A OCPD.

Cheers, Wayne

 

[jaggedben]

Yes, but 240.4(B) is optional. So if you choose not to use 240.4(B), and you choose to use the 60C ampacity, then #1 is the smallest Cu conductor size for a 100A OCPD.

Cheers, Wayne

I'll buy it, if for no other reason than to thumb my nose at 250.122(B) tbh. A fundamental problem with that section's wording is that it doesn't give us a baseline from which to judge if a conductor increased in size.

 

[wwhitney]

I'll buy it, if for no other reason than to thumb my nose at 250.122(B) tbh. A fundamental problem with that section's wording is that it doesn't give us a baseline from which to judge if a conductor increased in size.

Also, don't discount the Exception. If the circuit length is not so long that upsizing due to voltage drop would be in order, then the installer is a qualified person who may say "if I had used 60C wire for a 96A load on a 100A breaker, #1 Cu would be the smallest size allowed, and the normal EGC size would obviously be fine. Having a lower load or a higher temperature insulation on the conductor doesn't change whether that size EGC is an effective ground fault current path."

Cheers, Wayne

 

[david luchini]

Does this mean that if #1 THWN-2 is used then its limited to 130Amps but now the ground wire has to be upsized? sorry its confusing.

No. #1 Thwn-2 can be used at its 60deg ampacity per 110.14(C). Nothing is being upsized per the 250.122 requirements.

 

[LarryFine]

A fundamental problem with that section's wording is that it doesn't give us a baseline from which to judge if a conductor increased in size.

Agreed. At the very least, it should never have to be applied to an existing installation.

They certainly could have said, "Any time a conductor is larger than the minimum size required . . . "

We have also countered with, "But, I didn't increase the wire size, I reduced the breaker size."

 

[LarryFine]

No. #1 Thwn-2 can be used at its 60deg ampacity per 110.14(C). Nothing is being upsized per the 250.122 requirements.

 

[jaggedben]

They certainly could have said, "Any time a conductor is larger than the minimum size required . . . "

...

Even that is vauge. Is the 'minimum size required' the absolute minimum size that is required if I choose options and permissions that lead to the smallest conductor, or is it the largest conductor that can be justified by code requirements if I choose different options and ignore anything stated as a permissions?

They should change 250.122(B) to 'increased in size to reduce voltage drop' and let the AHJ be the judge of whether that is the reason.