Conductor ampacity

[tortuga]

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

Since we agree the term "termination provisions" means all types of "terminals", including pigtail leads, lugs terminal strips and not a branch circuit conductor then when you need to;
To determine the temperature limits (or minimum temperature ratings) of branch circuit or feeder conductors that attach to those terminations refer to 110.14(C) and 110.3(B)
To determine the ampacity of equipment termination provisions AKA the lug, terminal stip or pigtail ampacity refer to 110.14(C)(1) and 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.

 

[ggunn]

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

How is the ampacity at the termination any different from the ampacity anywhere else along the conductor? Is it really that hard to select a conductor that won't get any hotter than 75 degrees? After all, that's what all of this is about, isn't it?

 

[wwhitney]

Since we agree the term "termination provisions" means all types of "terminals", including pigtail leads, lugs terminal strips and not a branch circuit conductor then when you need to

I'm open to the idea (you still haven't provided a reference to the ROP you quoted), but it makes the first paragraph of 110.14(C)(1) very unclear, so I'm still unconvinced. You can't "determine" a terminal.

You seem to be arguing that 110.14(C)(1) is telling us something different than 110.14(C) first paragraph, that they are imposing different sorts of limits. My reading is that 110.14(C)(1) and (2) are elaborating on the general principle specified in 110.14(C) first paragraph by spelling out how it works in different cases.

Is the following a concrete example that illustrates the difference in interpretation? Say there is no ampacity correction or adjustment applicable, and say some #4 Cu 90C conductors come in on a 20' long messenger to a weatherhead, less than 2' of conduit, and then to a piece of equipment with 75C rated terminals which accept #4 to 250 MCM. I would say that 110.14(C) and 110.14(C)(1) together mean the ampacity is limited by the equipment to the 75C Table 310.16 ampacity of #4, which is 85A.

Do I understand correctly your position would be the following? The terminal has an ampacity at 75C of 255A per 110.14(C)(1) and Table 310.16. The 2' of conduit can be ignored per 310.14(A)(2) Exception. The wire on the messenger has an ampacity of 101A at 75C per Table 310.20 (and we are limited to 75C rather than 90C by 110.14(C)). So the setup is good for 101A.

I'm not buying the idea that the termination's ampacity doesn't depend on the wire that is connected to it. To get a Table 310.16 75C ampacity of 100A you'd need to use #3 Cu. If you connect #4 Cu to the termination and the current is 100A, the termination will run hotter than if you had used #3, due to the higher resistance of the connection itself and of the conductor immediately adjacent to the termination.

Cheers, Wayne

 

[wwhitney]

How is the ampacity at the termination any different from the ampacity anywhere else along the conductor?

Well, for one thing we don't apply ampacity adjustment or correction at terminations, for whatever reason. And for another we are limited to the termination temperature rating, which is generally 60C or 75C, while the conductor usually has 90C rated insulation. Plus there's the question of whether the termination requires us to use Table 310.16 with respect to the conductor size installed in the terminal, rather than the maximum size the terminal can take.

Is it really that hard to select a conductor that won't get any hotter than 75 degrees? After all, that's what all of this is about, isn't it?

My understanding of the equipment termination is this: the equipment is made and tested to a listing standard. In the typical case, that listing standard basically reproduces the relevant parts of Table 310.16. So if the equipment terminal rating is 75C, the equipment is tested with a conductor size based on the 75C column of Table 310.16 and the necessary current rating for the equipment. The listing standard will specify allowable temperature rises at various locations within the equipment, but the limit at the terminal itself is not necessarily 75C, it may be higher.

So I don't think it's quite as simple as saying nothing should get above 75C. It's more that the terminal rating of 75C means "at this connection, size your wire based on the 75C column of Table 310.16."

Cheers, Wayne

 

[kwired]

Well, for one thing we don't apply ampacity adjustment or correction at terminations, for whatever reason. And for another we are limited to the termination temperature rating, which is generally 60C or 75C, while the conductor usually has 90C rated insulation.

Terminations on equipment is usually 60 or 75C rated, even if they have 90C lugs attached to them. Many termination devices are rated 90C, some even higher and should be usable at those ratings as long as not attached to equipment with lower rating.

Is possible to run a circuit with conductors sized for 75C to the breaker, at some point splice to a 90C conductor with a 90C splicing device, run a conductor based on 90C ampacity for some distance and then splice it in similar fashion again to adapt back to 75C sized conductor before connecting to 75C terminals at the load equipment.

 

[ggunn]

So I don't think it's quite as simple as saying nothing should get above 75C. It's more that the terminal rating of 75C means "at this connection, size your wire based on the 75C column of Table 310.16."

But the language is driven by the intent of the code, which is to keep the terminals from exceeding their rated temperature.

 

[wwhitney]

But the language is driven by the intent of the code, which is to keep the terminals from exceeding their rated temperature.

The intent is definitely "don't size the wire too small and contribute to the terminals or equipment overheating." The question is whether that nominal 75C terminal rating specifically means that overheating is rising about 75C, or whether it's more nuanced.

If I get a chance, I'll try to look at an UL standard (for some equipment type) that talks about this, and check whether the temperature rise limit is in fact a limit that would correspond to a 75C peak temperature in 25C or 30C ambient.

Cheers, Wayne

 

[wwhitney]

But the language is driven by the intent of the code, which is to keep the terminals from exceeding their rated temperature.

Upon reflection, you are mostly right. If the terminal is rated 75C, with no other labeling, then that means we may terminate conductors with 75C rated insulation to them. Perforce that means that the terminal temperature should not exceed 75C, lest the conductor insulation be damaged. Of course that raises the question of what ambient temperature the listing standard requires the equipment to be tested in, but presumably we trust the listing standard writers to make reasonable choices in that regard.

But sometimes you encounter terminals with a warning similar to "Caution: use 90C rated conductors." Those terminals may still be "75C" rated for the purpose of sizing conductors. But because the temperature rose to above 75C (but presumably below 90C) during operational testing of the equipment, the use of higher temperature conductor insulation is required. In UL 1995 on HVAC equipment (what I was perusing while considering this), this is covered in section 45.11.

Ceiling mount luminaires are often an example of this 90C conductor requirement, although in that case the load is so low there's no real conductor sizing question.

Cheers, Wayne

 

[jim dungar]

Ceiling mount luminaires are often an example of this 90C conductor requirement, although in that case the load is so low there's no real conductor sizing question.

For heat producing items, like fixtures and 100% rated terminals, the requirement is usually for 90°C insulated conductors sized using the 75°C tables.

 

[tortuga]

I'm open to the idea (you still haven't provided a reference to the ROP you quoted), but it makes the first paragraph of 110.14(C)(1) very unclear, so I'm still unconvinced. You can't "determine" a terminal.

The original proposal 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:

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

and did not reference any particular ampacity table.

You seem to be arguing that 110.14(C)(1) is telling us something different than 110.14(C) first paragraph, that they are imposing different sorts of limits.

110.14(C) guides us with the selection of conductor size
and 110.14(C)(1) only applies to sizing "termination provisions".
I think most but not necessarily all UL listed equipment will have the limits of 310.16, but 110.14(C)(1) does not put an additional limit on anything other than non-listed equipment.
If you show 110.14(C)(1) to a 7th grade English teacher they would say the subject is "termination provisions" and not "conductor ampacities" and the action is to determine the ampacity of the subject
"termination provisions" and to do that you need to choose a conductor ampacity table, and it says which one to choose.
Per the NEC style manual

https://docinfofiles.nfpa.org/files/AboutTheCodes/70/NEC_Style_Manual_2023_v2.pdf

2.1.2.8 States:
"Synonyms, Similar Terms, or Alternate Terms. If the defined term has synonyms, similar
terms, or alternate terms associated with the main term that all are to be understood as having the
same definition, the base term being defined shall be followed by the alternate term in parentheses."

So 'termination provisions' cannot have the same meaning as 'conductor ampacity'.

And 2.1.6.3.3
"References to Subdivisions. References to subdivisions within a requirement shall include
the section number prior to the subdivision."
110.14(C) does not refer to 110.14(C)(1) and or 110.14(C)(2)
So those paragraphs stand on their own.
If your not in a situation where you need to determine "termination provisions" ampacity, such as when equipment is UL listed, then its safe to ignore 110.14(C)(1) and follow the instructions in the listing 110.3(B)

 

[wwhitney]

and 110.14(C)(1) only applies to sizing "termination provisions".

If "termination provisions" means "terminals," which you are arguing and which I am considering, then the NEC has nothing to say about sizing terminals. That's on the equipment manufacturer and the applicable UL standard.

I think most but not necessarily all UL listed equipment will have the limits of 310.16, but 110.14(C)(1) does not put an additional limit on anything other than non-listed equipment.

For listed equipment, using 310.16 is not an additional limit beyond what the listing standard says, but 110.14(C)(1) also tells us that when the listing standard allows for something else, the equipment will be so marked. So we don't have to go chasing listing standards, we can just look at the equipment marking. I am still interested in examples of equipment that is marked for use of something other than Table 310.16 for termination ampacities.

If you show 110.14(C)(1) to a 7th grade English teacher they would say the subject is "termination provisions" and not "conductor ampacities" and the action is to determine the ampacity of the subject "termination provisions" and to do that you need to choose a conductor ampacity table, and it says which one to choose.

If you mean 110.14(C)(1) first paragraph, and if you mean "subject" as in "subject of a sentence", then the subject of sentence one is the word "determination", and of sentence two is "conductor ampacities". The structure of those two sentence is where "termination provisions = terminals" does not parse properly.

If you mean "subject" as in "topic," I agree that 110.14(C)(1) (including (a) and (b) or not) is about termination provisions.

Anyway, I've lost track in these minutiae of parsing language what our actual disagreement is, so I need a concrete example where we would come to different conclusions. Would you consider and respond to the rest of post 163?

Cheers, Wayne

 

[ggunn]

Upon reflection, you are mostly right. If the terminal is rated 75C, with no other labeling, then that means we may terminate conductors with 75C rated insulation to them. Perforce that means that the terminal temperature should not exceed 75C, lest the conductor insulation be damaged.

But I am usually using 90 degree wire, so protecting the conductor insulation isn't the issue. The 75 degree heat limit at the terminal is to preserve the integrity of the connection between the terminal and the conductor. For me, this usually means choosing a 90 degree conductor based on what would be its 75 degree ampacity.

 

[wwhitney]

But I am usually using 90 degree wire, so protecting the conductor insulation isn't the issue.

FWIW the wording of UL 1995 (HVAC Equipment) 45.11 permits the possibility of a terminal rated 75 degrees with the further instruction to use a minimum 105C rated conductor. That means size based on 75 degrees but the terminal operating temperature may exceed 90C. Other than that case (and similar allowances in other equipment listing standards), I agree.

The 75 degree heat limit at the terminal is to preserve the integrity of the connection between the terminal and the conductor.

Sure, for a terminal marked just 75C. For a terminal marked "75C, use 90C conductor insulation", the terminal temperature may exceed 75C even when the conductors is sized based on the 75C rating. The tests of the listing standard presumably include checking that the integrity of the connection is not compromised by the higher temperature.

Cheers, Wayne

 

[ggunn]

For a terminal marked "75C, use 90C conductor insulation", the terminal temperature may exceed 75C even when the conductors is sized based on the 75C rating.

Why would that be?

 

[tortuga]

If you mean 110.14(C)(1) first paragraph, and if you mean "subject" as in "subject of a sentence", then the subject of sentence one is the word "determination",

The "subject" of a sentence must be person, place, or thing that performs the action in the sentence;

The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or
(C)(1)(b).

The person, place, or thing is "termination provisions of equipment", the action is determining what those are.
I think in all your other examples we would end up in the same place but I'd go with 110.3(B) instructions in the listing and labeling, not 110.14(C)(1).
Unless you want to discuss sizing termination provisions in non-listed equipment such as motor leads in a NEMA motor I don't think 110.14(C)(1) applies to sizing a conductor.

 

[ggunn]

The "subject" of a sentence must be person, place, or thing that performs the action in the sentence;

The person, place, or thing is "termination provisions of equipment", the action is determining what those are.

No, sorry; the subject of the sentence is the word "determination", which is a noun.

 

[wwhitney]

The "subject" of a sentence must be person, place, or thing that performs the action in the sentence;

The person, place, or thing is "termination provisions of equipment", the action is determining what those are.

You are 100% wrong on the grammar. In the sentence "The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b)," the subject is the word "determination." The words "of termination provisions of equipment" are a prepositional phrase modifying the noun "determination". The verb is either "shall", "shall be," or "shall be based"; if not the latter, the rest of "shall be based" is some sort of verb modifier (I've apparently forgotten this part of 7th grade English). The further prepositional phrase "on 110.14(C)(1)(a) or (C)(1)(b)" is modifying the verb or verb phrase.

Anyway, I'd prefer to stop arguing about grammar and have a more application based discussion. So in that vein I will regroup by restating my understanding: For any piece of equipment whose termination is labeled just "75C Cu" with no other labels (and the number etched into the lug is not a termination label in this sense), if you need to bring 90A to it, you always need to use a copper conductor of size at least #3 Cu with insulation temperature at least 75C. Per 110.14(C) and it's reference to Table 310.16. No exceptions.

Unless you want to discuss sizing termination provisions in non-listed equipment such as motor leads in a NEMA motor I don't think 110.14(C)(1) applies to sizing a conductor.

What possible other purpose could 110.14(C)(1) have? In restricting the types of conductor (insulation temperature rating) you can use, and how you can use them, it has an effect on the minimum size conductor you can connect to the equipment terminal.

Cheers, Wayne

 

[tortuga]

No, sorry; the subject of the sentence is the word "determination", which is a noun.

Woops OK send me back to 7th grade

What possible other purpose could 110.14(C)(1)

Lots of equipment need not be listed, you gave an example of HVAC equipment, but 440 does not require a listing, 424.6 requires certian heaters to be listed, motors need not be listed that I know of.

 

[wwhitney]

Why would that be?

Because there are other sources of heat present than just the resistance of the copper, the contact resistance of the termination, and the resistance of the internal wiring? And that heat will affect the temperature at the terminal.

Below is an example photo of a light fixture (fluorescent in this case, I believe) with the type of label under discussion; it says "Min. 90C supply conductors." That doesn't mean you get to use the 90C ampacity of the supply conductors; I expect 110.14(C)(1)(a) applies so you'd be limited to the Table 310.16 60C column for conductor sizing.

Cheers, Wayne

 

[wwhitney]

Lots of equipment need not be listed, you gave an example of HVAC equipment, but 440 does not require a listing, 424.6 requires certian heaters to be listed, motors need not be listed that I know of.

I see no language in 110.14(C) restricting any part of it to unlisted equipment. You are correct that for listed equipment, 110.3(B) also probably bears on the question, but 110.14(C) still applies, and is more directly on point.

Cheers, Wayne