Conductor ampacity

[Jaybone812]

Fixed it for you. The NEC is not the only enforceable code in many jurisdictions.

Cheers, Wayne

Fair enough. You are def correct lol. I appreciate you keeping me honest in every thread !

 

[tortuga]

Ugh now you made me go look at 486A-B. That seems to cover both lugs and other terminations that a piece of equipment might use, and wire connectors like wire nuts that would be used in the middle of a circuit, rather that at equipment terminations.

Here's a quick overview of the two current tests required. I'll use #4 Cu as an example, which the standard says has an "assigned maximum ampere rating" of 85A, it's 75C ampacity per Table 310.16.

1) Current cycling of 140A (75C rated connectors) or 175A (90C rated connectors) for 500 cycles over 1 hour with 50% duty cycle. The connector is permitted a 125C temperature rise over ambient.

2) A static heating test at 125A, until equilibrium temperature is reached. The connector is permitted a 50C temperature rise over ambient [with a note that higher temperature rises are permitted if the connector is for end use in equipment in which the application permits higher temperature rises]. If the heating follows I²*R, then the 50C temperature limit implies that at 85A (75C base ampacity of #4 Cu), the temperature rise would be at most 23C, while at 95A (90C base ampacity of #4 Cu), the temperature rise would be at most 29C.

[And that for the current cycling current of 140A, the equilibrium temperature rise for 140A would be at most 62C, half the allowable 125C. So the current cycling test is apparently looking for effects that would raise the termination resistance R and thereby increase heating.]


I believe it is tested both for #4 AWG and for 250MCM, on the assumption that if those behaviors pass, any intermediate wire size would pass. My skimming of 486A-B was not thorough enough to say that with 100% confidence. Certainly for connectors that are rated for mixed Al and Cu, there is discussion of testing with minimum size Al, minimum size Cu ; maximum size Al, minimum size Cu; etc.

Cheers, Wayne

Correct there are a few different ways connectors are tested, a connector can have a declared ampacity, I dont see a graduated limit on ampacity of a connector based on the wire size attached to it anywhere in UL 486A-B.
In section 7.3.1 the 50C temp rise test refers to the continuous carry the current Table 7 or Table 8.
looking at the examples in the back and Table 11 minimum samples, I think if a lug (connector) is rated for say 200 amps that is not tied to a 310.16 wire size, there is actually a note (c) on Table 7 that refers to 310.17.
Some of the temperature tests for copper conductors are waived if they pass with aluminum conductors.

This sentence in 110.14(C) only applies to sizing the
equipment termination provisions (wire connector or lug) to a 310.16 conductor size and ampacity, I don't see it as requiring the conductor attached to the lug to be sized that way;
"Unless the equipment is listed and marked otherwise,
conductor ampacities used in determining equipment termination
provisions shall be based on Table 310.16 as appropriately
modified by 310.12"

The way I read that is:
"To determine equipment termination
provisions use a conductor ampacity from Table 310.16 as appropriately
modified by 310.12, unless you test the equipment
and get it listed and marked otherwise"

I Just don't seen anything in that text to preclude a 75C 150A lug from being able to be terminated on a smaller conductor that is installed with the free air (as defined) 310.17 150A 75C ampacity.

 

[wwhitney]

Eh, the NEC doesn't care about the equipment lugs or their amp rating, all it cares about it is the termination temperature rating (and I guess Al vs Cu). So the phrase "equipment termination provisions" can only mean "sizing the wire that lands on that termination," as that wire size is what the NEC cares about.

The listing standard for equipment is going to specify what size wire lead the equipment is tested with. Every chart in every listing standard I've looked at (which admittedly is only a handful) reproduces Table 310.16. So when the temperature rise tests are done on the equipment they are done with a conductor sized from Table 310.16. That's why the field electrician needs to use a conductor at the termination sized via Table 310.16 as well (unless the equipment is listed and marked otherwise).

Cheers, Wayne

 

[ggunn]

Eh, the NEC doesn't care about the equipment lugs or their amp rating, all it cares about it is the termination temperature rating (and I guess Al vs Cu). So the phrase "equipment termination provisions" can only mean "sizing the wire that lands on that termination," as that wire size is what the NEC cares about.

I'll admit that I haven't done the research but I would make a small wager that this is because terminals' max current rating always exceeds the maximum ampacity of the largest conductor that will fit so that conductor temperature is always the limiting factor.

 

[Jaybone812]

Eh, the NEC doesn't care about the equipment lugs or their amp rating, all it cares about it is the termination temperature rating (and I guess Al vs Cu). So the phrase "equipment termination provisions" can only mean "sizing the wire that lands on that termination," as that wire size is what the NEC cares about.

The listing standard for equipment is going to specify what size wire lead the equipment is tested with. Every chart in every listing standard I've looked at (which admittedly is only a handful) reproduces Table 310.16. So when the temperature rise tests are done on the equipment they are done with a conductor sized from Table 310.16. That's why the field electrician needs to use a conductor at the termination sized via Table 310.16 as well (unless the equipment is listed and marked otherwise).

Cheers, Wayne

Well said

 

[david luchini]

I believe it is tested both for #4 AWG and for 250MCM, on the assumption that if those behaviors pass, any intermediate wire size would pass. My skimming of 486A-B was not thorough enough to say that with 100% confidence. Certainly for connectors that are rated for mixed Al and Cu, there is discussion of testing with minimum size Al, minimum size Cu ; maximum size Al, minimum size Cu; etc.

Per UL 486-A-B, the connector is tested for the largest conductor in the range of conductors. The termination's rating is the current per 310.16 for the largest conductor that the termination will accept.

 

[wwhitney]

The termination's rating is the current per 310.16 for the largest conductor that the termination will accept.

Seems to me the rating in the example from tortuga is "75C, #4 AWG - 250 MCM, Cu only". What code or standard can you point to that attaches an ampere value to the termination rating, independent of the conductor size?

To my understanding, the ampere value is only determined after you select a conductor size, and is then the Table 310.16 75C ampacity of that conductor size. So the ampere rating would be 85A for #4 Cu, 100A for #3 Cu, etc., up to 255A for 250 MCM.

Cheers, Wayne

 

[wwhitney]

Per UL 486-A-B, the connector is tested for the largest conductor in the range of conductors.

If you mean only the largest conductor in the range of conductors, do you have a reference within UL 486-A-B? The following suggest to me it would be both the largest and smallest:

UL 486-A-B 7.1.6A says in part "Testing covers conductor sizes that are within the cross-sectional area envelope of the sizes tested, as determined by the circular mils of the conductor." I take that to mean if you test two different sizes, it covers all the intermediate sizes as well (the "envelope")

And the description for the first test discussed, the current cycling test, begins at 7.2.1 with "The specimen sets shall complete 500 cycles of equal current-on and current-off operation for the periods of time specified in Table 7, other than as noted in 9.2.2 and 9.2.5, while carrying the 60 Hz test current specified for the connector temperature rating and conductor size being tested." That reference to "conductor size being tested" certainly suggests the same connector may be tested with multiple sizes.

But other than 7.1.1(i), which discusses the requirements for testing of connectors for mixed materials (e.g. copper conductors to aluminum conductors), I didn't see any explicit statement of the form "any connector to be listed for a range of conductor sizes shall be tested with each of the conductor sizes within the range (or the largest and smallest conductor sizes with the range) (or just the largest size of the range, although that would make no sense)."

Cheers, Wayne

 

[tortuga]

the NEC doesn't care about the equipment lugs or their amp rating,

The NEC specifies guidelines for manufacturers all the time, field electricians just don't notice it.
In many code articles they can be found under 'construction specifications'

the phrase "equipment termination provisions" can only mean "sizing the wire that lands on that termination,"

The topic of the sentence is "conductor ampacities" the phrase "used in determining equipment termination provisions" functions as a (reduced) relative clause that modifies "conductor ampacities," indicating the context in which these ampacities are being referenced, so how could 'termination provisions' and 'conductor ampacities' be the same thing in that sentence?

That would be like writing:
"Unless the equipment is listed and marked otherwise,
conductor ampacities used in determining conductor ampacities
shall be based on Table 310.16 as appropriately
modified by 310.12"

 

[tortuga]

What code or standard can you point to that attaches an ampere value to the termination rating, independent of the conductor size?

UL 486-A-B. See around section 8, then if you don't pick an ampacity it goes on
"8.2 For a connector without an assigned ampere rating , specimens shall be tested using the maximum size conductor or conductors"

 

[wwhitney]

Below is all of 2017 NEC 110.14(C)(1).

What does this phrase "termination provisions" mean? It's a phrase that the (2017) NEC only uses in 110.14(C)(1), or in informational notes that reference 110.14(C)(1). We are going to have to figure it out entirely from context within 110.14(C)(1).

So what does the first sentence tell us? Whatever "termination provisions" means, we determine it based on 110.14(C)(1)(a) or (b). OK, what sorts of options does (a) give us? It's different choices for conductor insulation temperature rating we can use, and how to use that rating.

So "termination provisions" apparently refers to what conductor insulation temperature rating we are allowed to use at the termination, and how we use it. And the second sentence of 110.14(C)(1) tells us that unless the equipment is listed and marked otherwise, whatever temperature rating we end up being allowed to use, to translate that into an ampacity, we use Table 310.16.

This is the plain and obvious meaning, and the second sentence even tells you how to overcome this limitation if you want to, you list and mark the equipment otherwise.

Cheers, Wayne

(1) Equipment Provisions. The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.15(B)(16) as appropriately modified by 310.15(B)(7).

(a) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
(1) Conductors rated 60°C (140°F).
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60°C (140°F) ampacity of the conductor size used.
(3) Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
(4) For motors marked with design letters B, C, or D, conductors having an insulation rating of 75°C (167°F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity.

(b) Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for one of the following:
(1) Conductors rated 75°C (167°F)
(2) 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, or up to their ampacity if the equipment is listed and identified for use with such conductors

 

[wwhitney]

The topic of the sentence is "conductor ampacities" the phrase "used in determining equipment termination provisions" functions as a (reduced) relative clause that modifies "conductor ampacities," indicating the context in which these ampacities are being referenced, so how could 'termination provisions' and 'conductor ampacities' be the same thing in that sentence?

I never said they are. I initially suggested "termination provisions" meant "sizing the wire that lands on that termination". Substitute that into the second sentence of 110.14(C)(1), and you get a very reasonable meaning:

"Unless the equipment is listed and marked otherwise, conductor ampacities used in (determining) sizing the wire that lands on the termination shall be based on Table 310.16 . . ."

My just prior post gives an alternate interpretation of the phrase "termination provisions," although not one that results in any different answers.

Cheers, Wayne

 

[tortuga]

I never said they are. I initially suggested "termination provisions" meant "sizing the wire that lands on that termination".

Wayne if you look at ROP it says

The term "termination provisions" is used so that all types of "terminals", including pigtail leads, will be included.

If "termination provisions" was a synonym for "conductor ampacity" then that would be a violation of the NEC style manual 2.1.2.8.
110.14(C) is from back when UL had a 'green book' and did not intend to add any new requirements but to address what a code instructor thought was installers not flowing the UL green book, the whole section might be outdated now, really the section that should govern this is 110.3(B) as the UL green book no longer exists.

 

[wwhitney]

If "termination provisions" was a synonym for "conductor ampacity"

Twice I've talked about the idea that "termination provisions" could mean "sizing the wire" (which would be part of the provisions the field electrician makes for terminating the wiring, as opposed to the provisions the manufacturer makes to allow wire to be terminated to the equipment), and twice you've responded as if I said "conductor ampacity."

Sizing a wire means selecting the physical size of wire (and conductor material, so maybe "selecting" is better than "sizing") you are going to use at the termination. You have to consider the conductor material the termination is rated for, the size range it accepts, the ampacity you require, temperature rating considerations (what we are currently discussing) as well as perhaps voltage drop. So again, I've never suggested that "termination provisions" was a synonym for conductor ampacity.

Cheers, Wayne

 

[wwhitney]

Wayne if you look at ROP it says

That text is interesting. What ROP are you talking about? The one that added 110.14(C) to the NEC? If so, please provide a complete reference so I can look it up.

So let's say that "termination provisions" is just a slightly obfuscated way to say "terminals" or "terminations". The phrase "termination provisions" is used 4 times in (2017) NEC 110.14(C). If we substitute "terminals" for "termination provisions", the last two usages parse nicely. But the first two usages, which is where a text that introduces a new term should give us hints about what that term means don't. The second usage is the sentence we seem to be arguing about, and it becomes:

"Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment terminals shall be based on Table . . ."

That doesn't really make sense, how does one "determine" an equipment terminal? Seems like it should be "conductor ampacities used at equipment termination provisions (terminals)" or something similar. So this wording is what led me to the idea that "termination provisions" must mean something about a process the field electrician undertakes, which could involve some "determining," like determining what size conductor to use. If "terminals" is really what is meant, it's some pretty bad wording.

Either way, the meaning of that sentence is that if we land #4 Cu 75C or 90C on an equipment terminal marked "75C Cu" and marked with a conductor size range that includes #4, with no other markings, we look at Table 310.16 and see that the ampacity of that connection is 85A. Pretty simple.

Cheers, Wayne

P.S. I would be very interested if anyone can point to an actual product that is "listed and marked otherwise." I'd like to read the product documentation and see how it talks about the issue, as well as peruse the applicable UL listing standard for the equipment.

 

[tortuga]

Twice I've talked about the idea that "termination provisions" could mean "sizing the wire" (which would be part of the provisions the field electrician makes for terminating the wiring, as opposed to the provisions the manufacturer makes to allow wire to be terminated to the equipment), and twice you've responded as if I said "conductor ampacity."

Sizing a wire means selecting the physical size of wire (and conductor material, so maybe "selecting" is better than "sizing") you are going to use at the termination. You have to consider the conductor material the termination is rated for, the size range it accepts, the ampacity you require, temperature rating considerations (what we are currently discussing) as well as perhaps voltage drop. So again, I've never suggested that "termination provisions" was a synonym for conductor ampacity.

Cheers, Wayne

The first paragraph of 110.14(C) and more importantly 110.3(B) covers what the OP is asking about, the sub paragraph 110.14(C)(1) only is titled "Equipment Provisions" and clearly is only enforceable for the determination of "termination provisions of equipment", thats motor leads, terminal strips, lugs, that sort of stuff.

 

[wwhitney]

UL 486-A-B. See around section 8, then if you don't pick an ampacity it goes on
"8.2 For a connector without an assigned ampere rating , specimens shall be tested using the maximum size conductor or conductors"

So I perused UL 486-A-B again, and it appears that you and @david luchini may be correct that for a connector that accepts only a single conductor material (aluminum or copper) and a range of sizes, the current testing portion of UL 486-A-B is only required for the largest size conductor accepted. [For connectors that accept multiple conductor materials, like copper and aluminum, and multiple sizes, 7.1.1(i) clearly states the current tests need to be done with different combinations, like the maximum size of one material and the minimum of the other.]

Upon reflection, I see that it is plausible that the largest size conductor is the worst case for terminal heating when we restrict the conductor ampacity to a fixed temperature rating. With that restriction, ampacity of a conductor with diameter d varies as approximately d^1.5. Plausibly the contact resistance varies as the reciprocal of the contact area. If we take the model that the contact area is a (proportional part of a) cylinder of fixed length, the contactarea varies with d. Then the I²*R heating from the contact resistance would vary as d³/d¹ = d², and the largest diameter is the worst case for heating, when the conductor is carrying its ampacity.

However, I don't see what bearing this observation has on the question of whether a terminal can be used with a conductor carrying a current in excess of its ampacity at the terminal temperature rating if that conductor is smaller than the terminal's maximum conductor size and the current is less than the ampacity of the maximum conductor size at the terminal's temperature rating. Either physics-wise or code-wise.

Cheers, Wayne

 

[wwhitney]

The first paragraph of 110.14(C) and more importantly 110.3(B) covers what the OP is asking about, the sub paragraph 110.14(C)(1) only is titled "Equipment Provisions" and clearly is only enforceable for the determination of "termination provisions of equipment", thats motor leads, terminal strips, lugs, that sort of stuff.

As to the very first post, it's not clear to me if it is referencing terminating conductors on equipment or not. But that is certainly what the discussion ultimately led to and what we've been discussing.

But I think I agree with the rest of what you said. I don't see how that bears on our disagreement or why you mention it?

Cheers, Wayne

 

[tortuga]

As to the very first post, it's not clear to me if it is referencing terminating conductors on equipment or not.

The OP is referencing 110.14(C) sub paragraph (1) as determining conductor ampacity:

After reviwing the nec 110.14(C)(1) it is apparent that a lot of electricians have been determing wiring ampacity wrong

The sub paragraph 110.14(C)(1) is titled "Equipment Provisions" and is only enforceable for the determination of "termination provisions of equipment".

 

[wwhitney]

The sub paragraph 110.14(C)(1) is titled "Equipment Provisions" and is only enforceable for the determination of "termination provisions of equipment".

OK, so what does that mean? It means the ampacity of the circuit at the termination.

So for the common case that a single wire type and size is run from termination to termination, the OP is correct that the ampacity at the termination often controls the choice of wire type and size.

Cheers, Wayne