Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
I don't know if I understand your comment sir.
Is it that I used "circuit" ampacity when I should have used something like "conductor" ampacity?
Conductor ampacity
- Thread starter Jpflex
- Start date
I don't know if I understand your comment sir.
Is it that I used "circuit" ampacity when I should have used something like "conductor" ampacity?
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
How can a circuit have an overall ampacity?
- Location
- Connecticut
- Occupation
- Engineer
I'm not sure. Like you mention, "circuit ampacity" were your words.
But, nothing in the AALZ's language or 110.14(C) says anything about the conductor ampacity either.
Just to recap what I think was or is being debated here;
- What the definition of "termination provisions" is (I say based on the 1993 code proposal its Lugs, motor leads, terminal strips etc)
- Does "termination provisions" include the circuit conductors attached to them (I say no)
- Does 110.14(C) say we shall determine "termination provisions" based on 110.14(C)(1) every time or only if they have not been determined by say the manufacturer (listed and marked otherwise)? ( I think you only need to refer to 110.14(C)(1) if the equipment is not listed and labeled as all listed equipment will include this info. )
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
That's patently false. In 110.14(C), the phrases "ampacity of a/the/such conductor," "conductor ampacity/ampacities," and "their ampacity" are used 7 times. In AALZ "Appliance and Utilization Equipment Terminations" and "Distribution and Control Equipment Terminations" similar phrases are also used 7 times.
Cheers, Wayne
- Location
- Connecticut
- Occupation
- Engineer
OK...I'll re-phrase. As I've already noted, nothing in 110.14(C) (nor in AALZ) says anything about selecting the ampacity of the conductor.
310.15(A) says... Ampacities for conductors rated 0 to 2000 volts SHALL BE AS SPECIFIED in the Ampacity Table 310.16 through 310.21, as modified by 310.15(A) through (F) and 310.12.
Table 310.16 through 310.21. Not just 310.16. Not "use the other tables as long as you don't exceed the values in 310.16."
- Location
- Connecticut
- Occupation
- Engineer
As I've already mentioned...
110.14 is titled Electrical Connections., not Ampacities for Conductors.
110.14(C) is titled Temperature Limitations, not Ampacities for Condcutors.
110.14 is titled Electrical Connections., not Ampacities for Conductors.
110.14(C) is titled Temperature Limitations, not Ampacities for Condcutors.
- Location
- Connecticut
- Occupation
- Engineer
As has been mentioned....
370.80 says...The ampacity of conductors in a cablebus SHALL be in accordance with 310.17 and 310.19 for installations up to and including 2000volts.... Not in accordance with 310.17 and 310.19, as long as they don't exceed the values in 310.16.
392.80(A)(2)(a) says...the ampacities for 600kcmil and larger single-conductor cables in uncovered cable trays shall not exceed 75 percent of the ampacities in Table 310.17 and Table 310.19. Not, shall not exceed 75% of 310.17 and 310.19, as long as you don't exceed 310.16.
370.80 says...The ampacity of conductors in a cablebus SHALL be in accordance with 310.17 and 310.19 for installations up to and including 2000volts.... Not in accordance with 310.17 and 310.19, as long as they don't exceed the values in 310.16.
392.80(A)(2)(a) says...the ampacities for 600kcmil and larger single-conductor cables in uncovered cable trays shall not exceed 75 percent of the ampacities in Table 310.17 and Table 310.19. Not, shall not exceed 75% of 310.17 and 310.19, as long as you don't exceed 310.16.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
The point of the term "ampacity" and the associated rules is to prevent overheating due to an undersized conductor. Either overheating of the conductor itself, or overheating of the equipment to which it is terminated.
So without getting into a debate about the appropriateness of and difference between terms like conductor ampacity, wire ampacity, termination ampacity, circuit ampacity, etc. we can say the following:
Selection of the size of a wire at a termination at a piece of equipment is governed by 110.14(C), the UL AALZ Category Info, 210.19(A)(1)(a), 215.2(A)(1)(a), 230.42(A)(1), and any similar more specific sections like 690.8(B)(1).
Selection of the size of a wire elsewhere is governed by 310.14/310.15, 210.19(A)(1)(b), 215.2(A)(1)(b), 230.42(A)(2), and any similar more specific sections like 690.8(B)(2).
Also 240.4 in conjunction with NEC sections like 210.20 and 215.3 that impose minimum size OCPD requirements also affect the choice of conductor size; not sure if those requirements can be incorporated into the previous dichotomy.
Cheers, Wayne
So without getting into a debate about the appropriateness of and difference between terms like conductor ampacity, wire ampacity, termination ampacity, circuit ampacity, etc. we can say the following:
Selection of the size of a wire at a termination at a piece of equipment is governed by 110.14(C), the UL AALZ Category Info, 210.19(A)(1)(a), 215.2(A)(1)(a), 230.42(A)(1), and any similar more specific sections like 690.8(B)(1).
Selection of the size of a wire elsewhere is governed by 310.14/310.15, 210.19(A)(1)(b), 215.2(A)(1)(b), 230.42(A)(2), and any similar more specific sections like 690.8(B)(2).
Also 240.4 in conjunction with NEC sections like 210.20 and 215.3 that impose minimum size OCPD requirements also affect the choice of conductor size; not sure if those requirements can be incorporated into the previous dichotomy.
Cheers, Wayne
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Well, the language in 110.14(C) appears to impose limits on how we apply 310.15 at least with respect to the choice of temperature column in those tables. So I would say that is something about selecting the ampacity of a conductor.
But before elaborating on that, let me ask a couple honest questions (reflecting actual uncertainty on my part, not for rhetorical purposes) about how the NEC uses the term ampacity, or how you consider we should use it in discussion. Let's say "wire segment" means a continuous unspliced length of non-rigid (no busbars) conductor.
1) After applying all the relevant NEC rules and requirements, do we end up with a single ampacity for any given wire segment in any given installation? Or terminologically, does it make sense for some installations to say "this wire segment has this ampacity at this point; and some other ampacity at some other point"?
2) If the answer to (1) is a single ampacity for a wire segment, suppose in 30C ambient a 90C #4 Cu wire segment runs in a cable with at most 3 CCCs from a breaker labeled 60C/75C in a panelboard labeled 75C to the main lugs of another panelboard labeled 75C. Is the ampacity of that wire segment 85A (Table 310.16 75C value) or 95A (Table 310.16 90C value)?
Thanks,
Wayne
- Location
- Connecticut
- Occupation
- Engineer
Per UL 486A-B, a connector for a range of conductor (say #4 through #3/0) will be tested with the largest conductor....#3/0.
But not only that, it will be at 310 Amps for the static heating test, and 345 Amps for the 75 deg rated connector Current-cycling test....
But sure, if I use a #1/0 conductor with a 200A load in a 40degF refrigerated warehouse on that #4-#3/0, 75deg connector, I'm totally going to exceed the temperature rating of the connector because the conductor is smaller than #3/0....I think not.
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
I used circuit and conductor interchangeably in that post. I understand why that might have been confusing.
Circuits can have a rating.
Conductors and terminations have an ampacity.
The ampacity of the conductors and terminations shouldn't be less than the circuit's rating. That would, by extension, create a rated ampacity for a given circuit since we are not speaking to specifics. When we actually make these choices we start with the load, move to wire ampacity and ensure the termination provisions are adequate for the load. No different than wire selection. But since we are talking about this vaguely, the "wire's ampacity" is the "circuit's rating" unless we get specific.
I don't want this to pull us away from the purposes of the discussion.
Terminations, no different than wire, shouldn't be installed in a way that their rating is exceeded. They are not rated the same way as wire. Hence the whole part about flexible cords, cable bus, cable tray, being in free air, or in a conduit duct bank underground. The wire or conductor method used may not always have a rating that matches the table 310.16, but the equipment and terminals are rated based on it.
We are constantly adjusting the ampacity of the conductors to the conditions of the installation. I don't understand why we wouldn't do the same for equipment terminations.
AALZ and 110.14(C) tell us exactly how to determine the terminations' listed rating and adds information about the responsibility to also meet the rated use of the equipment. Which is not always the same. IAEI has a wonderful article to help with understanding the limitations due to termination and equipment ratings.
I say 310.14(A)(2) covers that, more than one ampacity can apply, the exception is what I call the 10' or 10% rule.
Nice article, when it says;
We can all perhaps agree then you only need to follow the temperature rating already identified on the equipment labeling per 110.3(B), thus effectively we need not apply 110.14(C)(1) unless you need to perform the determination of termination provisions yourself?
Since 110.14(C) does not say "the provisions for terminations of equipment shall be determined as per 110.14(C)(1) regardless of any listing or labeling", 110.14(C)(1) says how to make 'the determination' but not that you always have to make it, the only time you would need to determine the termination provisions is if its not done already and that would be if the equipment is not listed or is field assembled.
With 110.14(C)(1) and 110.(3)(b) You end up in the same place most of time but not always, such over 600V,
The article is from before the big 600V -> 1000V or less conversion it states:
Now part 3 of 110 is for 'over 1000V' not 'over 600V', so at the time of the article terminations on a 690Y/400V or 1000Y/577V system were understood to be based on 90°C falling under 110.40 but now they fall under 110.14(C).
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
No, I do not agree.
Also, I still don't know what termination provisions are as far as the usage in 110.14(C). The usage in AALZ is consistent with termination provisions meaning lugs et al. But then AALZ is describing what the manufacturer has done per the listing standards and what is therefore expected from the installer. Whereas 110.14(C) are instructions for the installer, and several uses of the term "termination provisions" in 110.14(C) become unclear if you substitute "terminals" for "termination provisions". I guess if you further assume that "determination" means "determination of how to use" that works for 110.14(C). Otherwise the literal meaning of those sentences would be instructions on how to choose the lug or terminal to use, something the manufacturer has already done for us.
I'm willing to go with "determination of termination provisions" means "determination of how a termination may be used," which more or less means I think "termination provisions" is being used in 110.14(C) to mean "how a termination may be used."
If I look up the definition of "provision", I get a few options, one of which is "(1) the action of providing or supplying something for use." That would make sense for the manufacturer, they are providing the terminal. But I also get "(3) a condition or requirement in a legal document." That seems to be more how 110.14(C) is using the word.
No. The sentence plainly applies to all equipment, listed or not. For your interpretation to be valid, it would have to say "for terminations of unlisted equipment," but that's not what it says and not what it means.
As always with 110.3(B), there will be overlap between what the NEC requires and what a listing requires. Hopefully the two are coordinated so they don't conflict and largely are simply duplicates.
Cheers, Wayne
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Let's see, 310.14(A)(2) says (excluding the exception) "Where more than one ampacity applies for a given circuit length, the lowest value shall be used."
I don't find this helpful in resolving the question of "one ampacity per wire segment" vs "one ampacity per location on a wire." I don't see how how more than one ampacity can apply "for a given circuit length (with each ampacity applying to the whole given length)." If I take it to mean instead "where more than one ampacity applies to different portions of a given circuit length," that makes sense, as the conditions of use can change so different portions of the length could have different ampacity.
But then we have "the lowest value shall be used". That could mean "the portion at the higher ampacity gets demoted to the lower ampacity, so now the entire circuit length has just one ampacity". Or it could mean "the different portions do still have different ampacities, but where any other NEC requirement refers to the ampacity of that "circuit length", you need to use the lowest value."
Even looking at the definition of ampacity is unclear on this question: "The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating." That could mean "since the conditions of use can change at different points on the conductor, the ampacity can change at different points." Or it could mean "for the entire conductor, consider all the conditions of use that exist anywhere, and choose the maximum current such that no where will the conductor exceed its temperature rating."
I guess I should submit a 2029 PI that changes the definition to "The maximum current, in amperes, that a conductor can carry continuously under the conditions of use at a given point without exceeding its temperature rating." If accepted, that would make it clear that ampacity refers to a given point on the conductor and can change along the length of the conductor. If not accepted, the panel statement might make it clear that they intend for the entire length of the conductor to have a single ampacity.
Cheers, Wayne
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Sure, but 110.14 mentions ampacities of conductors, and it is certainly plausible that the connections can affect the ampacity of the conductor.
And again 110.14(C) mentions ampacities of conductors, and it is certainly plausible that the selection of temperature limit can affect the ampacity of the conductor.
Cheers, Wayne
I would said 85A. Because 110.14 (C) Temperature limit. 95A can be used for adjustment, correction or both.
"The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both"
I think we need to agree on what termination previsions are, as I posted earlier the original proposal of110.14(C) is good place to check, it can be found in the 1993 A1993 Technical Committee Reports (TCR) [Articles 90- 250]
Log # 1429 by Peter Schram (One of the handbook author's) stated:
If the equipment is not listed then no manufacturer has done that for you and then you (the installer) use 110.14(C)(1) to determine termination provisions. Nothing in 110.14(C) requires an installer to redetermine a termination provision as per 110.14(C)(1) for listed and labeled equipment.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
For the static heating test, the allowable temperature rise is 50C, so that may be usefully informative (as far as the physics) as to the thermal behavior at lower currents. Of course you'll have to figure out how to adjust for smaller conductor sizes; the contact resistance may increase with smaller conductors, so it is not enough just to compare currents and ignore the conductor size.
For the current cycling test, the allowable temperature is 125C, so I don't think that will be helpful in arguing that some other practical conditions won't exceed 75C.
Regardless, to the extent that UL 486A-B requires testing at currents in excess of the Table 310.16 values (which it incorporates as the "Assigned maximum ampere rating" column in Table 7), that is presumably to provide a margin of error, and does not constitute permission or even a reason to use ampacities in excess of the Table 310.16 values.
To give this example the benefit of the doubt, let's say the load is interlocked with a thermostat so that it will never operate at temperatures above 40F (5C). So I infer you'd like to take credit for the ambient temperature being 25C below the 30C design temperature in Table 310.16. A 75C ampacity from that Table is based on a 45C maximum temperature rise over 30C ambient. So with a 70C maximum temperature rise over a 5C ambient, the ampacity would increase by a factor of sqrt(70/45) = 1.248.
The 75C ampacity of 1/0 Cu is 150A per Table 310.16. With the 1.248 temperature correction, if applicable, we would get a 75C ampacity of 187A. So even if this is an allowable method, with the numbers you have chosen, 200A is too much. But we could massage some of the numbers to make it work, e.g. use a 2/0 Cu conductor (75C table ampacity 175A), or lower the load to 185A, or lower the temperature further.
I agree that this method make sense physics-wise. But it is not permitted under 110.14(C) or the AALZ guide-info. That is 100% explicit for the case of AALZ "Distribution and Control Equipment Terminations," which says to use the Table 310.16 values without correction. It's less explicit but still true for 110.14(C) and AALZ "Appliance and Utilization Equipment Terminations."
It is not so uncommon that the regulations do not cover all usage cases with the full allowances that would make sense on the basis of the physics. Simplifications are made to permit ease of administration and understanding by the general use. I have encountered this with multiple PIs to expand the allowances to 705.12(B). In the last round the CMP's response to my proposals was to paraphrase "you're probably right on the physics, but we're not going to further complicate 705.12(B). You can do what you want under 705.12(B)(6)'s "under engineering supervision" provision."
If there is a comparable "under engineering supervision" provision applicable to your example and 110.14(C), then as an engineer you could reasonably stamp a design for the use of 2/0 Cu conductors for a 200A load in your example, or 1/0 Cu for a 185A load. Otherwise, you are out of luck and required to design with 3/0 Cu with no credit for the lower ambient temperature.
Cheers, Wayne