Is everything I know wrong?

[wwhitney]

It can't say that, as saying that would not permit you to use the 90°C ampacities for ampacity adjustment and correction.

Are you saying that the language in 110.14(C)(1)(a) on equipment with 60C terminals does not permit the use of 75C or 90C ampacities for ampacity adjustment and correction?

Cheers, Wayne

 

[jaggedben]

It can't say that, as saying that would not permit you to use the 90°C ampacities for ampacity adjustment and correction.

No, because the second sentence of the introductory paragraph to 110.14(C) makes it explicitly clear that that is permitted regardless.

Is there some different logic at play in (a) and (b) that requires the wording to be different?

The intent is that where the adjusted and corrected ampacity of the 90°C conductor exceeds that of a 75°C conductor, you cant use the 90°C conductor at an ampacity that exceeds the table ampacity as found in the 75°C column.

But what it actually says is that you can't use the 90C conductor. Period. Even if the adjusted and corrected ampacity does exceed the 75C cloumn. It just stops there. It's simply wrong, counter to the intent you describe, and counter to common sense and practice. Needs to be fixed.

 

[wwhitney]

But what it actually says is that you can't use the 90C conductor. Period. Even if the adjusted and corrected ampacity does exceed the 75C cloumn. It just stops there. It's simply wrong, counter to the intent you describe, and counter to common sense and practice. Needs to be fixed.

That's one way to read "provided," but given the nonsensical result you have to read it the alternative way I proposed. I do agree it should be fixed, though, as it is unnecessarily ambiguous.

I do have a couple things I'm unsure about as far as how the NEC uses the term ampacity:

1) My inference is that the ampacity of an unspliced conductor is the minimum of the ampacities that would apply to it at any point along its length (including terminations) if considered in isolation. So for a 90C conductor terminated at a 75C piece of equipment, the conductor's ampacity is limited to the tabular 75C value, as that termination is part of the conductor's conditions of use. Is that how it is commonly understood? As opposed to saying, no, the conductor's ampacity is still the 90C ampacity with adjustment and correction, but the equipment limits the conductor's use to a lower current value.

The definition from Article 100 "Ampacity. The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating." suggests the latter, but the way 110.14(C) is written suggests the former. It seems to me that if the former is intended, the definition of ampacity would be clearer if it included at the end "or the temperature rating of its terminations."

2) The phrases "60C ampacity," "75C ampacity," and "90C ampacity" always refer the tabular values from Article 310 without adjustment or correction. That is the inference I make from the way they are used, but it would be nice to see that spelled out somewhere.

Cheers, Wayne

 

[jaggedben]

Wayne it's not 'unnecessarily ambiguous', it's simply wrong. Incorrect. Erroneous. Misworded. And you are not 'reading it a different way', you are employing knowledge gained elsewhere to (correctly) determine that it must mean the opposite of what it says. And it does not matter what the vague instance of 'ampacity' refers to, it comes up with a wrong result each way.

Any example bears this out.

For example suppose I have 110A of circuit current. The 310.16 ampacity of #2 copper is 115A at 75C and 130A at 90C. Assume 75C rated terminals like normally encountered in the real world.
Therefore I can use 75C rated #2.
I cannot use 90C rated #2 without making adjustments or corrections, because the 90C ampacity naturally exceeds the 75C ampacity.
More ridiculously, I cannot use any 90C conductor that is upsized for voltage drop, because the ampacity exceeds the 75C ampacity.
Finally, if my adjusted and corrected ampacity for #2 happens to come out to, say, 112A, I can use #2 because that ampacity 'does not exceed' the 75C ampacity of 115A.

'does not exceed' should read 'exceeds'. It's a straight up error.

 

[don_resqcapt19]

Are you saying that the language in 110.14(C)(1)(a) on equipment with 60C terminals does not permit the use of 75C or 90C ampacities for ampacity adjustment and correction?

Cheers, Wayne

no

 

[don_resqcapt19]

No, because the second sentence of the introductory paragraph to 110.14(C) makes it explicitly clear that that is permitted regardless.

Is there some different logic at play in (a) and (b) that requires the wording to be different?



But what it actually says is that you can't use the 90C conductor. Period. Even if the adjusted and corrected ampacity does exceed the 75C cloumn. It just stops there. It's simply wrong, counter to the intent you describe, and counter to common sense and practice. Needs to be fixed.

I think it is perfectly clear, but if you don't, you have plenty of time to write of a PI and substantiation to make a correction in the 2026 code. They will be due in mid September of 2023. The system should be open for PI submissions sometime in October of 2022.

 

[jaggedben]

I think it is perfectly clear, but if you don't, you have plenty of time to write of a PI and substantiation to make a correction in the 2026 code. They will be due in mid September of 2023. The system should be open for PI submissions sometime in October of 2022.

Point taken. I'll mark my calendar.

I do think it's weird how so many people who have a lot of experience in the industry can go through so many code cycles thinking that it is 'perfectly clear' that when it says 'x must not exceed y' that means 'x must exceed y'.
ggunn's initial sarcasm about the "clarity and precision that we have come to expect from the NEC" is apt.

 

[wwhitney]

Wayne it's not 'unnecessarily ambiguous', it's simply wrong.

I disagree, although this argument is a bit silly as I think we both know what it's supposed to say. The point where we deviate:

I cannot use 90C rated #2 without making adjustments or corrections, because the 90C ampacity naturally exceeds the 75C ampacity.

Now if the code section said "90C ampacity" then I would agree with you, as 90C ampacity means the tabular entry. But it doesn't, it just says "ampacity". Ampacity is a derived value starting from some table entry, with various multipliers and other possible limits. As such, the sentence can be read as imposing an additional limit on ampacity, rather than just "compute one value and compare it to another." And that is how everyone reads it.

BTW, I still would be interested to know if people agree with my points (1) and (2) above, as my comments are based on those inferences.

Cheers, Wayne

 

[jaggedben]

Now if the code section said "90C ampacity" then I would agree with you, as 90C ampacity means the tabular entry. But it doesn't, it just says "ampacity". Ampacity is a derived value starting from some table entry, with various multipliers and other possible limits. As such, the sentence can be read as imposing an additional limit on ampacity, rather than just "compute one value and compare it to another." And that is how everyone reads it.

...

Wayne, this totally doesn't matter one whit. Whatever number you think the 'ampacity' is, there are only three possibilities.
1) That ampacity exceeds the 75C ampacity, in which case the language prohibits the conductors use.
2) The ampacity does not exceed the 75C ampacity, but exceeds the circuit current. Then the language allows the conductor's use, even though Don and everybody else says it doesn't. It's also narrow band of possibilities that has no point in the real world.
3) The ampacity is less than the circuit current, in which case some other code section is going to disallow its use.

All of these results are nonsensical and wrong. The point hinges not-at-all on the precise meaning of ampacity.

 

[wwhitney]

Your list of possibilities presumes that ampacity is some number determined by other rules, and that the phrase "Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity of the conductor size used" involves checking that number against the 75C ampacity.

That's not the only reading, which should be clear, since everyone else is reading it differently. The other reading is that the rule is not about the "ampacity as determined elsewhere" but rather the "ampacity value to be determined in accordance with various rules, including this one." In which case the sentence just says that when you determine that ampacity, it can not exceed the 75C table ampacity.

Also, I don't follow your case #2 above. I don't think anyone is arguing that if you have a 100A breaker with a calculated 100A non-continuous load and a conductor with 75C table ampacity of 110A and a 90C ampacity adjusted for conditions of use that comes out to 105A that you can't terminate that conductor on that breaker.

Cheers, Wayne

 

[wwhitney]

Let me put it another way. If you say, in the midst of various rules about how many candles to put on a birthday cake, "the number of candles may be one candle per year of the celebrant's age, provided that the number does not exceed 20." Most people are going say that a 25 year old would get 20 candles under that rule, not that the rule is inapplicable because 25 > 20.

Cheers, Wayne

 

[jaggedben]

Okay, after some effort, I finally see your point. You are saying that 'does not' should be read as 'is not considered to'.

Thus: "conductors with higher temperature ratings [may be used], provided the ampacity of such conductors is not considered to exceed the 75C ampacity of the conductor size used."

Would you not agree that is a hundred times less open to misinterpretation?

ggunn's sarcasm is still 100% warranted.

 

[wwhitney]

I'm glad our notions of reality have come into alignment, thanks for sticking with it.

If I were going to make a small edit to clarify (rather than rewrite from scratch), I would replace "does not exceed" with "is limited to". Or even just changes "does" to "may".

Cheers, Wayne

 

[jaggedben]

I'm glad our notions of reality have come into alignment, thanks for sticking with it.

If I were going to make a small edit to clarify (rather than rewrite from scratch), I would replace "does not exceed" with "is limited to". Or even just changes "does" to "may".

Cheers, Wayne

You are still allowing too much ontological essence here. None of your suggested changes sufficiently clarify that what the ampacity 'is' is not as determined by all the other rules in the code. This is important because higher up in the section it tells us to use Article 310 to determine ampacity. Then, per your intepretation, it tells us to throw all that out if it exceeds the 75C ampacity. That needs to be clearer.

 

[ggunn]

The inspector went for it. I told him that however I got to the correct wire size I could use the next up OCPD. He agreed. Imagine that.