Possible Pattern w/ 110.14(C) and 310.15(B) ... Check My Math, What Do You Think?

[Jerramundi]

Using your logic, as I see it, we would never be allowed to use larger conductors to combat voltage drop.

Fair point about upsizing wires for voltage drop. I'll have to think about how that applies and how that argument could potentially defeat my interpretation and get back to you.

We're just discussing guys and guys... and if I'm wrong, then it's all for the better that I brought this issue to your attention and you corrected me. That's the purpose of this forum, IMO.

You gotta be willing to take the risk of being wrong in public discourse if you're ever going to learn anything... or on the flip side of things, change anything for the better... and unfortunately, I don't have any private resources at my disposal other the actual code book. My private resources are busy drinking beer in a garage somewhere right now and don't want to talk to me because I make their brains hurt with all my questions, lol.

I no so good at being good soldier worker boy. I ask too many questions, lol.

 

[wwhitney]

I don't see how "selection and coordination" yields a "may (must)" scenario. "Selection and coordination," as I read it, are descriptive words of the action we're taking and nothing more.

May/must was referring to how the termination rating relates to the temperature rating. So if the termination is listed as 60/75C and you use 75C conductors, you may use the 75C or the 60C columns. While if the conductor is rated 90C but the termination is rated 60C, you must use the 60C column for the termination limits.

This is the CRUX of what I'm talking about in how I initially read these code sections in trying to figure out how 110.14(C) and 310.15(B) work together and how I came up with the OP.

Right, I think this is the only real point of disagreement now. The sentence in 310.15(B) doesn't really tell us what to do when "the corrected and adjusted ampacity does exceed the ampacity for the temperature rating of the termination in accordance with the provisions of 110.14(C)."

Note that we don't need that 310.15(B) language to have the permission to use the higher temperature rating of the conductor as the basis for ampacity correction and adjustment, as 110.14(C) already provided that permission. 310.15(B) is just reminding us of that.

So when the corrected and adjusted ampacity does exceed the termination ampacity, we just use the lesser value, the termination ampacity. I.e. in your OP, the red boxes are not violations, they are just cases where the ampacity is limited by the termination to 30A. I agree this isn't spelled out, but it is how it is commonly understood, and it is what makes sense physics wise, at least for ampacity adjustment.

Now an interesting question is why ampacity correction doesn't apply to terminations.

Cheers, Wayne

 

[wwhitney]

P.S. See Annex D Example D3(a), the section on Ungrounded Feeder Conductors, for an example supporting the standard interpretation.

Cheers, Wayne

 

[Little Bill]

@Jerramundi

If I had four 12-2 NM cables for a 20A circuit and they were in conduit, or they were bundled through a fire stopped hole, I would have to derate for more than three CCC.
I would have nine (9) CCC. Could I still use a 20A breaker after derating?

 

[Jerramundi]

Simple answer. As long as the final value is not less than 15A and you meet all the requirements of 240.4(B), then yes.

Complex answer. I don't know why I'm even addressing this question, but I'll play.

After this answer please allow us to continue discussing 110.14(C) and 310.15(B), because that's what were trying to resolve here. I can see how this could be considered relevant, but it's mostly just a distraction as far as I'm concerned.

If I had four 12-2 NM cables for a 20A circuit....

For one, I assume you are NOT paralleling four 12-2's for a single 20A circuit, because that would be certifiable, lol.
I assume you mean four 12-2 NM cables for four 20A circuits.

...and they were in conduit, or they were bundled through a fire stopped hole, I would have to derate for more than three CCC.

Bundling them through a fire stopped hole would NOT require you to derate (adjust) in the manner of having more than three CCC's.
It would require you to derate (correct) in the manner of ambient temperature correction per 334.80 Ampacity, but the amount that you would have to correct by would depend on the ambient temperature, which you have not provided.

If they were in a raceway, which I don't know why you would do that, less a few specific circumstances,
even though the number of CCC's in an individual cable does NOT exceed 3, that would still qualify as more than three CCC's in a raceway and require adjustment per 310.15(B)(3)(a).

I would have nine (9) CCC.

No, you would have 8, but the same factor of 0.70 would apply.
Is this a joke because I'm having a DISCUSSION with some mods as opposed just downloading their answers that you feel the need to joke about supplying me with an inaccurate count? Because it's really not funny or clever.

Could I still use a 20A breaker after derating?

Per 334.80 Ampacity you would have to set their ampacity per the 60*C column at 20A and derate from the 90*C column at 30A "provided the final derated ampacity does not exceed that of a 60*C conductor," which is eerily similar to what we're discussing here and the only reason I'm taking interest in this question.

So 30A * 0.70 * X = Y | X = ambient temperature correction factor; Y = final adjusted and corrected ampacity

Going with the highest 2% design temperature from Copper.org for Tennessee, which is 97*F, and assuming we take a value from the 60*C column of T310.15(B)(2)(a), which I'm honestly not sure if we should do, because I believe the actual conductors within NM are THHN 90*C conductors, but 334.80 requires us to treat NM like a 60*C conductor, then we have a ambient temperature correction of 0.82

So 30A * 0.70 * 0.82 = 17.22A, which satisfies the requirements of 334.80 Ampacity.

If you DID meet the requirements of 240.4(B), then yes, 20A breaker.
If you DID NOT meet the requirements of 240.4(B), then no, 15A breaker.

How'd I do?

Please don't bother addressing each portion of this response, I would like to finish have a discussion with the rest of the people in the thread @wwhitney and the others. We're making progress and this is just throwing a wrench in the gears.

 

[wwhitney]

Bundling them through a fire stopped hole would NOT require you to derate (adjust) in the manner of having more than three CCC's.

334.80 second paragraph says that you do, assuming the firestop is in the form of "thermal insulation, caulk, or sealing foam," as I generally understand it would be.

Also, 334.80 first paragraph bears on the issue under discussion which is why Little Bill asked the question: "The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final calculated ampacity does not exceed that of a 60°C (140°F) rated conductor."

So the question is, if you assume 30C ambient (since it was unspecified in the example), the 90C adjusted ampacity would give you 21A (30A * 0.7), which is greater than the 60C unadjusted ampacity of 20A. Then do you say (a) ok we can't use the 90C starting value of 30A, let's redo the computation with the 75C starting value of 25A, so the answer is 0.7 * 25 = 17.5A? Or (b) that the "provision" is that the final calculated ampacity has a ceiling of 20A, so since we calculated >20A, we reduce to 20A, and the answer is 20A.

This is a real world example, as for a circuit with multiple receptacles on it, if you want to use a 20A OCPD, you need at least 20A ampacity, you can't round up via 240.4(B). And the widely understand answer above is (b), not (a) as your OP suggests.

Have you reviewed the Annex D3(a) example yet?

Cheers, Wayne

 

[Little Bill]

Simple answer. As long as the final value is not less than 15A and you meet all the requirements of 240.4(B), then yes.

Complex answer. I don't know why I'm even addressing this question, but I'll play.

After this answer please allow us to continue discussing 110.14(C) and 310.15(B), because that's what were trying to resolve here. I can see how this could be considered relevant, but it's mostly just a distraction as far as I'm concerned.


For one, I assume you are NOT paralleling four 12-2's for a single 20A circuit, because that would be certifiable, lol.
I assume you mean four 12-2 NM cables for four 20A circuits.


Bundling them through a fire stopped hole would NOT require you to derate (adjust) in the manner of having more than three CCC's.
It would require you to derate (correct) in the manner of ambient temperature correction per 334.80 Ampacity, but the amount that you would have to correct by would depend on the ambient temperature, which you have not provided.

If they were in a raceway, which I don't know why you would do that, less a few specific circumstances,
even though the number of CCC's in an individual cable does NOT exceed 3, that would still qualify as more than three CCC's in a raceway and require adjustment per 310.15(B)(3)(a).


No, you would have 8, but the same factor of 0.70 would apply.
Is this a joke because I'm having a DISCUSSION with some mods as opposed just downloading their answers that you feel the need to joke about supplying me with an inaccurate count? Because it's really not funny or clever.


Per 334.80 Ampacity you would have to set their ampacity per the 60*C column at 20A and derate from the 90*C column at 30A "provided the final derated ampacity does not exceed that of a 60*C conductor," which is eerily similar to what we're discussing here and the only reason I'm taking interest in this question.

So 30A * 0.70 * X = Y | X = ambient temperature correction factor; Y = final adjusted and corrected ampacity

Going with the highest 2% design temperature from Copper.org for Tennessee, which is 97*F, and assuming we take a value from the 60*C column of T310.15(B)(2)(a), which I'm honestly not sure if we should do, because I believe the actual conductors within NM are THHN 90*C conductors, but 334.80 requires us to treat NM like a 60*C conductor, then we have a ambient temperature correction of 0.82

So 30A * 0.70 * 0.82 = 17.22A, which satisfies the requirements of 334.80 Ampacity.

If you DID meet the requirements of 240.4(B), then yes, 20A breaker.
If you DID NOT meet the requirements of 240.4(B), then no, 15A breaker.

How'd I do?

Please don't bother addressing each portion of this response, I would like to finish have a discussion with the rest of the people in the thread @wwhitney and the others. We're making progress and this is just throwing a wrench in the gears.

I wasn't trying to deceive or trick you. I did make a couple of typos or missed info. Yes, the (4) NM cables were for (4) circuits of 20A each
Yes I had something else on my mind when I wrote (9) CCC, I meant (8).
This example is as relevant as all the other paths you have taken to discuss this. At one point, you seemed to indicate that you didn't think we could use the 90 deg column to derate something that is limited to the 60 deg column. I was giving a real world example of that.
As Wayne mentioned, you do derate for running NM through fire stopped holes if there are more than (3) CCC. Same as if in a conduit or raceway.

 

[infinity]

As Wayne mentioned, you do derate for running NM through fire stopped holes if there are more than (3) CCC. Same as if in a conduit or raceway.

Similar but not the same. You derate when there is more than 2 cables in a sealed hole. With 2 cables you could technically have up to 8 CCC's and no derating required.

 

[Jerramundi]

334.80 second paragraph says that you do, assuming the firestop is in the form of "thermal insulation, caulk, or sealing foam," as I generally understand it would be.

You are correct. I looked at T310.15(B)(3)(a) and thought it was referencing T310.15(B(2)(a-b) because it seemed absolutely ridiculous to me that simply passing through a hole together would trigger adjustment. Being that it talks about thermal insulation, I think the word thermal made me think ambient temperature correction needed to be applied.

Even though I still think simply passing through a hole together triggering any form of derating seems ridiculous. Running for a longer distance together in a conduit sure, but passing a mere 1.5" through a top plate and we lose ampacity? What? Sprecka-da-Englash?

Also, 334.80 first paragraph bears on the issue under discussion which is why Little Bill asked the question: "The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final calculated ampacity does not exceed that of a 60°C (140°F) rated conductor."

Agreed and as I said, was the only reason I was taking interest in his question.

So the question is, if you assume 30C ambient (since it was unspecified in the example)...

Would you say that this is the correct way to approach the question? Assume 30*C (86*F) if it is unspecified?? I suppose if you received this question on an exam, you couldn't just plug in any ambient temperature that you want and I was kind of being a dick by choosing the ambient temperature from Tennessee, where @Little Bill states he's located. Sorry Billy. *Insert sad Gizmo face*

So the question is, if you assume 30C ambient (since it was unspecified in the example), the 90C adjusted ampacity would give you 21A (30A * 0.7), which is greater than the 60C unadjusted ampacity of 20A. Then do you say (a) ok we can't use the 90C starting value of 30A, let's redo the computation with the 75C starting value of 25A, so the answer is 0.7 * 25 = 17.5A? Or (b) that the "provision" is that the final calculated ampacity has a ceiling of 20A, so since we calculated >20A, we reduce to 20A, and the answer is 20A. And the widely understand answer above is (b), not (a) as your OP suggests.

I understand what you're saying. I just don't see anywhere in the code that gives us permission to do that, other than possibly 210.3 which states "where conductors of a higher ampacity are used for any reason, the ampere rating of the... [OCPD] shall determine the circuit rating."

IMO, what 210.3 is saying, is that if we have a final corrected and adjusted ampacity of say 21A and choose to put a 20A breaker on it, the circuit is now rated at 20A. That's pretty clear and I don't have any issues with that.

However, the way this reads to me, is that we still have to follow the rules of 110.14(C), 310.15(B), and in @Little Bill's example, 334.80, in the process of calculating our final correct and adjusted ampacity. Nowhere does 210.3 give us permission to change the procedural rules outlined in the above sections for calculating our final corrected and adjusted ampacity.

And, in this example, as in 310.15(B), it's pretty clear IMO that we can only derate from the 90*C column IF the final corrected and adjusted ampacity is less than the 60*C amount. If our final corrected and adjusted ampacity is greater, we have failed to satisfy the prerequisite of being allowed to derate from the 90*C column and have not successfully completed the calculation, yet. Once the calculation is successfully completed then and only then can we apply something like 210.3.

That's how it reads to me. That's how I know IF statements to work from a brief exposure to computer programming in my younger years.
You can't just go superseding an IF statement like that, unless you're a hacker POS, lol.

Have you reviewed the Annex D3(a) example yet?

Briefly. Took me for a spin on some other code sections because I never work with industrial feeders and I ended up choosing to spend the end of the evening answering @Little Bill's question.

 

[Little Bill]

Similar but not the same. You derate when there is more than 2 cables in a sealed hole. With 2 cables you could technically have up to 8 CCC's and no derating required.

Point taken, but my point was the stopped hole would have to be derated under certain circumstances. It was in response to the statement made by the OP.

Bundling them through a fire stopped hole would NOT require you to derate (adjust) in the manner of having more than three CCC's.
It would require you to derate (correct) in the manner of ambient temperature correction per 334.80 Ampacity, but the amount that you would have to correct by would depend on the ambient temperature, which you have not provided.

 

[Jerramundi]

And, in this example, as in 310.15(B), it's pretty clear IMO that we can only derate from the 90*C column IF the final corrected and adjusted ampacity is less than the 60*C amount. If our final corrected and adjusted ampacity is greater, we have failed to satisfy the prerequisite of being allowed to derate from the 90*C column and have not successfully completed the calculation, yet. Once the calculation is successfully completed then and only then can we apply something like 210.3.

I just want to be clear about something here. This opinion of mine about how these sections read is only if dealing with a 60*C termination.

If we have 75*C terminations and we derate from the 90*C, say on a #12 THHN, we will more easily have a final corrected and adjusted ampacity that satisfies what I'm saying.

It makes sense to me that when working with 60*C terminations, a 90*C conductor, and derating from 90*C, that the requirements will be more restrictive than when working with 75*C terminations, a 90*C conductor, and derating from 90*C.

 

[infinity]

Point taken, but my point was the stopped hole would have to be derated under certain circumstances. It was in response to the statement made by the OP.

You're correct. If was just pointing out that the cables in the sealed hole have different rules than the more the 3 CCC's in a raceway.

 

[wwhitney]

You're correct. If was just pointing out that the cables in the sealed hole have different rules than the more the 3 CCC's in a raceway.

So if a manufacturer comes out with 12/5 NM cable, you can stuff (2) of those through a firestopped hole, and the CCC derating is based on 5 (each cable separately), not 10. But if you stuff 3 of them in the hole, the CCC derating is based on 15.

Cheers< Wayne

 

[Jerramundi]

So if a manufacturer comes out with 12/5 NM cable, you can stuff (2) of those through a firestopped hole, and the CCC derating is based on 5 (each cable separately), not 10. But if you stuff 3 of them in the hole, the CCC derating is based on 15.

Cheers< Wayne

Assuming that the theoretical 12/5 NM is marketed like all other NM products, that is, one of the 5 is not an EGC and it's 12-5 w/ Ground...

334.80 reads to me that if you put 2 x 12/5 NM through a firestopped hole, there would be no derating...
but if you put 3 of them through, you would derate based on 15 CCC's or 50% and the lower ampacity would apply to the entire cable, no exceptions.

Where do you get derating is based on 5 (each cable separately)?

 

[infinity]

So if a manufacturer comes out with 12/5 NM cable, you can stuff (2) of those through a firestopped hole, and the CCC derating is based on 5 (each cable separately), not 10. But if you stuff 3 of them in the hole, the CCC derating is based on 15.

Cheers< Wayne

Two cables, no derating regardless of how many CCC's your theoretical cable has. 3 cables derating applies.

 

[Jerramundi]

Assuming that the theoretical 12/5 NM is marketed like all other NM products, that is, one of the 5 is not an EGC and it's 12-5 w/ Ground...

334.80 reads to me that if you put 2 x 12/5 NM through a firestopped hole, there would be no derating...
but if you put 3 of them through, you would derate based on 15 CCC's or 50% and the lower ampacity would apply to the entire cable, no exceptions.

Where do you get derating is based on 5 (each cable separately)?

Correction to the previous post. I see now that you have to simultaneously look at 334.80 Ampacity AND 310.15(B)(3)(a) Adjustment Factors.

@infinity please check the below because I'm curious about this....

2 x 12-5 NM would NOT trigger 334.80 Ampacity because there is NOT more than two NM cables.
2 x 12-5 NM WOULD trigger 310.15(B)(3)(a) Adjustment Factors because the number of CCC's in a cable exceeds 3.
So we would have to adjust by 10 CCC's or 50%

The difference being that, because 334.80 Ampacity is NOT triggered, we can apply the exception in 310.15(A)(2) Selection of Ampacity and still allow for the larger ampacity.

3 x 12-5 NM WOULD trigger 334.80 Ampacity AND 310.15(3)(a) Adjustment Factors.
Now derating by 15 CCC's, still 50%

The difference being that because 334.80 Ampacity HAS been triggered, we CANNOT apply the exception in 310.15(A)(2) and MUST utilize the lower ampacity.

 

[wwhitney]

Two cables, no derating regardless of how many CCC's your theoretical cable has. 3 cables derating applies.

Any cable with more than 3 CCCs triggers derating, just like any raceway does. For NM, with derating based on the 90C ampacity and the final ampacity limited to the 60C ampacity, the derating is usually (always?) moot.

Cheers, Wayne

 

[infinity]

Correction to the previous post. I see now that you have to simultaneously look at 334.80 Ampacity AND 310.15(B)(3)(a) Adjustment Factors.

@infinity please check the below because I'm curious about this....

2 x 12-5 NM would NOT trigger 334.80 Ampacity because there is NOT more than two NM cables.
2 x 12-5 NM WOULD trigger 310.15(B)(3)(a) Adjustment Factors because the number of CCC's in a cable exceeds 3.
So we would have to adjust by 10 CCC's or 50%

The difference being that, because 334.80 Ampacity is NOT triggered, we can apply the exception in 310.15(A)(2) Selection of Ampacity and still allow for the larger ampacity.

3 x 12-5 NM WOULD trigger 334.80 Ampacity AND 310.15(3)(a) Adjustment Factors.
Now derating by 15 CCC's, still 50%

The difference being that because 334.80 Ampacity HAS been triggered, we CANNOT apply the exception in 310.15(A)(2) and MUST utilize the lower ampacity.

Yes the exception 10'/10% rule could apply when there are only two cables in the sealed hole.

 

[wwhitney]

And, in this example, as in 310.15(B), it's pretty clear IMO that we can only derate from the 90*C column IF the final corrected and adjusted ampacity is less than the 60*C amount. If our final corrected and adjusted ampacity is greater, we have failed to satisfy the prerequisite of being allowed to derate from the 90*C column and have not successfully completed the calculation, yet. Once the calculation is successfully completed then and only then can we apply something like 210.3.

Regardless of the lack of clarity of the 310.15(B) language referenced above, and that your interpretation is plausible on the face of it without any background, the intent and industry-wide understanding of 310.15(B) is not that you instead derate from the 75C or 60C column, but that you take the minimum of the 90C derated ampacity and the termination temperature un-derated ampacity.

Given the lack of clarity, a PI for the 2026 NEC would be an improvement. Until then, that's the best explanation you're going to get.

Cheers, Wayne

 

[Jerramundi]

Any cable with more than 3 CCCs trigger derating, just like any conduit does. For NM, with derating based on the 90C ampacity and the final ampacity limited to the 60C ampacity, the derating is usually (always?) moot.

Cheers, Wayne

Not moot. Feels that way out of frustration, just like talking about privacy in today's world does,
but if it were to result in an ampacity below the 60*C level, then it is definitely NOT moot.

And I understand the frustration here because it feels like, if we go by my interpretation in the OP, we will always end up with an ampacity below the 60*c column, but to be clear, my position is only based on the circumstance of having 60*c terminations.

If you had 75*C terminations and derated from 90*C, you could end up with something like 21A and be fine for a 20A circuit.

It seems to me, that you're better off looking for products with a min of 75*C ratings.
Be nice if everything just had 90*C ratings, but that would be too easy and some code people jobs might not be needed, lol.
All about that political holy grail, "jobs."