310.15 (A)(2)Ex. 10' or 10% ampacity

[Rich Elec.]

In the Sept./Oct. IAEI magazine Jim Pauley has an article "Understanding NEC rules about wire temperature ratings, ..."

Page 22 "Derating process example".

Last paragraph: I am going to paraphrase. This are the general ideas, so that I can get my question asked. I don't want to be too wordy.

"110.14 (C)(1) states, ... conductor ampacities used in determining equipment termination provisions shall be based on Table 310.16 as appropriately modified by 3105.15 (B)(1) through (6)."
"Other tables may be applicable for the conductors in a specific environment,"
"For instance, a single conductor installed in free-air may have its ampacity determined by Table 310.17. Examples of those circumstances where this may be useful include ambient derating and installation in a cable tray. However, at the point where the conductor is terminated in equipment, the ampacities of Table 310.16 will govern, This may require that a larger conductor be used or that the conductor size be changed prior to entering the equipment."

My question is: If "this may require that a larger conductor be used or that the conductor size be changed prior to entering the equipment.", in certain installations could the rule at 310.15(A)(2) Ex. apply?
10' or 10% of the circuit length the higher ampacity may be used.
Am I applying this rule correctly?

Thank you,
Rich

 

[Smart $]

IMO, you are applying the rule correctly. I feel many do not use this rule at times which they could because they simply do not understand it... and forget about it.

However, you must remember that 110.14(C) is regarding termination temperature ratings. Ampacity could be affected indirectly, and the exception to 310.15(A)(2) Ex. could be rendered moot.

You would have to enter the parameters of the termination temperature ratings in your example in order to determine whether 310.15(A)(2) Ex. could apply or not.

 

[hardworkingstiff]

It seems to me that since the FPN to 310.15(A)(2)Ex alerts you to the termination limitations of 110.14(C) that this exception would not apply to the requirements of 110.14(C).

I would be very interested in an example of when/how it would apply to override 110.14(C).

 

[Smart $]

It seems to me that since the FPN to 310.15(A)(2)Ex alerts you to the termination limitations of 110.14(C) that this exception would not apply to the requirements of 110.14(C).

I would be very interested in an example of when/how it would apply to override 110.14(C).

I would be, too.

However, I'm fairly certain there are none.

Yet Rich Elec has a good point in that not all installations have their conductor ampacities determined by Table 310.16. In that 110.14(C) recognizes 310.15(B)(6) as an "exception" which permits a higher ampacity than given in the Table is evidence of acceptance in principal... yet it falls short of other such installations (such as those falling under Table 310.17).

 

[hardworkingstiff]

I would be, too.

However, I'm fairly certain there are none.

Yet Rich Elec has a good point in that not all installations have their conductor ampacities determined by Table 310.16. In that 110.14(C) recognizes 310.15(B)(6) as an "exception" which permits a higher ampacity than given in the Table is evidence of acceptance in principal... yet it falls short of other such installations (such as those falling under Table 310.17).

Or, (in my work) 400.5(B)

 

[rbalex]

While I agree, that 310.15(A)(2) Exception should not apply when 110.14(C)(1) is the primary limiting “condition of use,”(I even made a Proposal to that effect) mull this over:

310.15 Ampacities for Conductors Rated 0–2000Volts.
(A)General.
…
(2) Selection of Ampacity. Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used.
Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.
FPN: See 110.14(C) for conductor temperature limitations due to termination provisions.
…

[RBA Note: Underlines added

1. Section 310.15(A)(2) and its Exception apply to "circuit lengths” and “circuits” – not only “conductors.”
2. Terminals are certainly “… adjacent portions of a circuit…” and usually less than “… 3.0 m (10 ft) or 10 percent of the circuit length...”
3. FPNs aren’t enforceable. Even if they were in this case, since 110.14(C)(1) specifically references Table 310.16 as its basis, terminals are simply one of potentially many “tabulated ampacities” to consider when applying 310.15(A)(2) Exception.

[RBA Note to Self: Remenber these points next time you make this Proposal ]

 

[Rich Elec.]

I do understand and agree that the 310.15 (A)(2) EX. should not apply when termination temperature ratings are the deciding factor.

The termination is labeled for 75 C and the wire is 90C the 310.15 (A)(2) EX. does not override the termination limitation, and allow the 90C ampacity for 100% of the circuit length.

The FPN directs us to 110.14 (C), but the FPN is not enforceable.
So should the FPN not be a fine print note?
Was that the proposal that you made Bob?
And if so, what was the result of your proposal?

 

[Rich Elec.]

Bob,
I see your proposal in the 2008 ROP's. I like your substantiation: "It recognizes that if the lowest ampacity value is determined by connections it is the overall limiting value."
But, the panel only addressed your FPN deletion. They did not address your addition of text. "Where an ampacity determined by 110.14 (C) is the lowest value this exception shall not apply." And in the online version that I have up, your addition of text is not underlined. Was the underline overlooked when this was typed up for printing? Was the CMP not aware of new text?

I think that you have a good point, and maybe this should be addressed again in the next code cycle. Because, again the FPN is not enforceable.

Rich

 

[Smart $]

...mull this over...

I have in the past, and asked here on the forum if this exception could supercede 110.14(C). I do not recall getting any response. So you are the first (other than myself... that I'm aware of) to even hint as to the possibility.

IMO, 310.15(A)(2) Exception can supercede 110.14(C) in cases where it can be shown the conductor termination temperature does not exceed it's rating. I believe the latter is necessary to maintain termination integrity as is the intention of 110.14(C).

[RBA Note to Self: Remenber these points next time you make this Proposal ]

Send a post link in or copy text into a PM to yourself... so it's easier to relocate at a later date.

 

[hardworkingstiff]

IMO, 310.15(A)(2) Exception can supercede 110.14(C) in cases where it can be shown the conductor termination temperature does not exceed it's rating. I believe the latter is necessary to maintain termination integrity as is the intention of 110.14(C).

Is there anyway to accomplish this without UL testing? If I understand 110.14(C), it's in there because of UL test methodology.

 

[Smart $]

Is there anyway to accomplish this without UL testing? If I understand 110.14(C), it's in there because of UL test methodology.

Hmm... I'd say your AHJ would be the first step. Ask if they'll permit 310.15(A)(2) Exception to supercede 110.14(C) because your conductor ampacities (and thus conductor temperatures) are determined by 400.5(B) [as you stated earlier] rather than Table 310.16 or 310.15(B)(6)... and see what they say. Worst-case scenario, they will say no.

The reason I say this is because the wording is there to permit such, but that depends heavily on your AHJ's interpretation of 310.15(A)(2) Exception and their understanding of the intent behind 110.14(C).

 

[hardworkingstiff]

Hmm... I'd say your AHJ would be the first step. Ask if they'll permit 310.15(A)(2) Exception to supercede 110.14(C) because your conductor ampacities (and thus conductor temperatures) are determined by 400.5(B) [as you stated earlier] rather than Table 310.16 or 310.15(B)(6)... and see what they say. Worst-case scenario, they will say no.

The reason I say this is because the wording is there to permit such, but that depends heavily on your AHJ's interpretation of 310.15(A)(2) Exception and their understanding of the intent behind 110.14(C).​

This is what I'm trying to do, understand the intent.

I keep thinking about "Charlie's rule". The one that says the code does not say what you think it says, it does not say what you want it to say, it says what is says.

From 110.14(C)1

Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment terminatinos provisions shall be based on Table 310.16 as appropriately modified by 310.15(B)(6).

Later in the commentary of the handbood

However, installers or designers unaware of the UL guide card information might attempt to select conductors based on a table other than Table 310.16. ....

That nails me, using table 400.5(B). I can only guess that although the cords can handle heat generated at higher ampacities (and the same temperature, 75C let's say) than building wire the termination cannot. I don't understand, 75C is 75C and if a cord can heat sink more heat than a THWN conductor, why wouldn't the termination be able to handle it if it is rated for the ampacity of the cord. IE: A #4 type W on a 100-amp breaker rated for 75C connections is not allowed by 110.14(C)(1). The breaker can handle 100-amps at 75C and the cord will apparantly heat sink 100-amps just fine at 75C, so why the issue?

 

[Pierre C Belarge]

From Lou
"That nails me, using table 400.5(B). I can only guess that although the cords can handle heat generated at higher ampacities (and the same temperature, 75C let's say) than building wire the termination cannot. I don't understand, 75C is 75C and if a cord can heat sink more heat than a THWN conductor, why wouldn't the termination be able to handle it if it is rated for the ampacity of the cord. IE: A #4 type W on a 100-amp breaker rated for 75C connections is not allowed by 110.14(C)(1). The breaker can handle 100-amps at 75C and the cord will apparantly heat sink 100-amps just fine at 75C, so why the issue?"


I would think that with so many variables in the field, and the general lack of knowledge by field installers, the CMP has decided to limit this type of installation. I know that a lot of manufacturers install wiring and equipment within their product one way, yet that practice may not be permitted in the field installation, due to the variables that occur in the field.
(I hope that helps, I completely understand what I wrote )

 

[Pierre C Belarge]

I know this has been mentioned before, but it bears repeating.

Manufacturers design equipment terminations with the intent that conductors are a heat sink for the terminals. I believe that is why 110.14 does supercede 310.15(A)(2). JMHO

 

[hardworkingstiff]

Does the ampacity rating at a certain temperature mean that up to that temperature the conductor will sink the heat generated by the ampacity?

(I sure hope that made sense)

 

[Smart $]

I know this has been mentioned before, but it bears repeating.

Manufacturers design equipment terminations with the intent that conductors are a heat sink for the terminals. I believe that is why 110.14 does supercede 310.15(A)(2). JMHO

I understand the "conductors are a heat sink for the terminals" principle. Yet for conductors whose ampacities are determined by tables other than 310.16, and where those ampacities are higher under the 75?C column, those conductors will sink more heat away from the termination for the same amount of current than will the same sized one one installed per T310.16.

For example, #12 Cu at 75?C under T310.16 has an ampacity of 25A. The same #12 Type W 3+ conductors at 75?C under T400.5(B) has an ampacity of 31A. So why should this or better rated multi-conductor cable type be limited to 25A when it is reasonable to assume it does not reach 75?C until it conducts 31A???

 

[Smart $]

...

For example, #12 Cu at 75?C under T310.16 has an ampacity of 25A. The same #12 Type W 3+ conductors at 75?C under T400.5(B) has an ampacity of 31A. So why should this or better rated multi-conductor cable type be limited to 25A when it is reasonable to assume it does not reach 75?C until it conducts 31A???

After thinking a little more about this, using #12 as an example is a poor choice. Consider the same comparison for a #8 or larger conductor.

 

[Smart $]

Does the ampacity rating at a certain temperature mean that up to that temperature the conductor will sink the heat generated by the ampacity?

(I sure hope that made sense)

For the sake of understanding the concept only, assume the terjmination is at its temperature rating (say 75?C). When the current on the conductor only warms the conductor up to any temperature less than 75?C, it acts as a heat sink, drawing heat away from the termination.. At 75?C the conductor and termination are at equilibrium. Conducting an amount of current which causes the conductor to exceed 75?C makes it a heat source as far as the termination is concerned, and the termination also exceeds 75?C.

 

[hardworkingstiff]

I understand the "conductors are a heat sink for the terminals" principle. Yet for conductors whose ampacities are determined by tables other than 310.16, and where those ampacities are higher under the 75?C column, those conductors will sink more heat away from the termination for the same amount of current than will the same sized one one installed per T310.16.

Exactly! So the only reason for the limitation to using 310.16 at the terminations is the UL testing?

 

[Pierre C Belarge]

For the sake of understanding the concept only, assume the terjmination is at its temperature rating (say 75?C). When the current on the conductor only warms the conductor up to any temperature less than 75?C, it acts as a heat sink, drawing heat away from the termination.. At 75?C the conductor and termination are at equilibrium. Conducting an amount of current which causes the conductor to exceed 75?C makes it a heat source as far as the termination is concerned, and the termination also exceeds 75?C.

A lot of the termination points today, terminals, lugs, breaker terminal; are listed at 90C. The lower rated ampacity will not exceed the terminal ratings.