yet more 110.14(C)

[Smart $]

Is it really so difficult to understand that a terminal doesn’t give a damn about any other condition of use a conductor may have except at the termination? And for a specific conductor material at a continuous current for terminals intended to be covered by 110.14(C), a terminal’s temperature is not affected by anything except the ambient temperature, the conductor’s size, and (rarely) the conductor’s stranding? The conductor’s insulation, i.e. “Type,” is irrelevant at the termination.

...

I agree with your statement quoted above, but only in part.

The issue under discussion, in its most basic form, is the temperature at a conductor's termination (more specifically, a proper termination). While the termination don't give a damn about any other condition of use, those other conditions of use may or will affect the temperature at the termination for a given amount of current on the circuit.

 

[hardworkingstiff]

Does any know why the ampacities in table 400.5(B) are higher at the same temperature rating than the ampacities in 310.16?

 

[rbalex]

I agree with your statement quoted above, but only in part.

The issue under discussion, in its most basic form, is the temperature at a conductor's termination (more specifically, a proper termination). While the termination don't give a damn about any other condition of use, those other conditions of use may or will affect the temperature at the termination for a given amount of current on the circuit.

Unless 110.14(C) recognizes an engineering solution, the properly applied 60?C and 75?C ampacities from Table 310.16 as possibly modified by 310.15(B)(6) and/or ambient temperatures, is all that is reasonably necessary to determine a conductor?s ampacity at the terminations intended to be covered by 110.14(C).

However, with the possible exception of generally allowing diversity to be considered, any other factor not already considered by a properly applied 110.14(C) would be trivial within reasonable safety factors - even with an engineering solution permitted. (Note 310.15(B)(6) is simply a specific case of applying diversity.)

Since diversity is already considered in proper load calculations, I seriously doubt an ?engineering solution? would be accepted in the first place. Therefore, I simply want 110.14(C) to be clear enough that people quit trying to impose it on a conductor?s temperature rating throughout the circuit.

 

[Smart $]

Unless 110.14(C) recognizes an engineering solution, the properly applied 60?C and 75?C ampacities from Table 310.16 as possibly modified by 310.15(B)(6) and/or ambient temperatures, is all that is reasonably necessary to determine a conductor?s ampacity at the terminations intended to be covered by 110.14(C).

Your comment I highlighted in red is a fallacy. First, 110.14(C) does not change a conductor's ampacity. It may, and does so in many cases, limit the circuit ampacity. In theory, should 110.14(C) impose such limitation, it is directly related to the temperature of the wire-type conductor at its termination(s) when it is conducting current continuously at the circuit ampacity level.

Currently, 110.14(C) does not recognize an engineering solution... as you are well aware of. If in the future an engineering solution is permitted, that would be great. However, there exists other conditions of installation where the conductor's temperature at its terminations can be deduced from ampacity tables other than Table 310.16.

However, with the possible exception of generally allowing diversity to be considered, any other factor not already considered by a properly applied 110.14(C) would be trivial within reasonable safety factors - even with an engineering solution permitted. ...

I do not agree with your trivial assessment. As in hardworkingstiff's case, permitting a circuit ampacity using a Type W cable installation that is near 15% greater than present impositions is, IMO, far from trivial. Compare copper conductor ampacities by percentage between 310.15(B)(6) and Table 310.16 75?C column...

4	85	100	18%
3	100	110	10%
2	115	125	9%
1	130	150	15%
1/0	150	175	17%
2/0	175	200	14%
3/0	200	225	13%
4/0	230	250	9%
300	285	300	5%
350	310	350	13%
400	335	400	19%

... (Note 310.15(B)(6) is simply a specific case of applying diversity.)

Since diversity is already considered in proper load calculations, I seriously doubt an ?engineering solution? would be accepted in the first place. Therefore, I simply want 110.14(C) to be clear enough that people quit trying to impose it on a conductor?s temperature rating throughout the circuit.

Diversity, as in this discussion, is simply a concept which ensures the conductor temperature at its terminations will likely never reach the temperature rating of the termination. You can see this concept in your mind's eye, as can I. But I see other conditions of installation where the same concept (but not diversity) is applicable.

 

[rbalex]

What is in red is NOT a fallacy; it's entirely consistent with the definition of ampacity:

Ampacity. The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

For a given conductor, each "condition of use" creates a different ampacity within the circuit. Assuming the conductor's "regular" insulation has been removed at the termination, its temperature rating is whatever is imposed by the termination. Its "regular" insulation and construction does come into play when determining its ampacity in other conditions of use.

Assuming a conductor is properly installed, only the conductor’s size and the ambient temperature have any significant effect on the conductor's ampacity at the termination. Because stranding permits deformation of the cross-section of the conductor, it may have some potential effect, but that is probably overcome by the overall increase in cross-section inside the termination.

Both Tables 310.16 and 400.5(B) are empirically derived. That is, while there are formulas and factors to adjust them, their original values were determined by measurements based on the worst performing conductor. They also have a healthy built-in safety factor.

As I stated before, Table 310.15(B)(6) recognizes diversity, Table 310.16 does not. You will also note the values listed in Table 310.15(B)(6) are Ampere ratings, the values listed in Table 310.16 are ampacities. They are not the same thing.

 

[Smart $]

What is in red is NOT a fallacy; it's entirely consistent with the definition of ampacity: "Ampacity. The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating."

Okay... let me restate what I meant in less ambiguous terms using "code-correct" terminology:

110.14(C) does not change a conductor's ampacity. It may—and does so in many cases—limit the circuit overcurrent rating to a value less than the conductor's ampacity. In theory, should 110.14(C) impose such limitation, it is directly related to the temperature of the wire-type conductor at its termination(s) when it is conducting current continuously at the circuit overcurrent rating level. What 110.14(C) does, in effect, is provide a method for the coordination and selection of a conductor size such that it establishes a circuit overcurrent rating that otherwise would have a greater value. Is that method all encompassing? Some believe so. I am not one of them.

For a given conductor, each "condition of use" creates a different ampacity within the circuit. Assuming the conductor's "regular" insulation has been removed at the termination, its temperature rating is whatever is imposed by the termination. Its "regular" insulation and construction does come into play when determining its ampacity in other conditions of use.

I agree, in essence...

First, an assumption the "regular" insulation has been removed is unnecessary. For example, even IDC terminations are subject to 110.14(C). For those that don't know, IDC stands for Insulation Displacement Contact (or Connector, or Connection, perhaps others, all depending on who you ask), and is considered to terminate (or tap, splice, etc. for other discussions) by displacing, not removing, the conductor insulation. However, for the sake of discussion, and to make a point later, I agree to consider the insulation to be removed at the conductor's termination.

Next, let us differentiate that your use of the term "temperature rating" I have highlighted in red is in fact the termination temperature rating, not the temperature rating associated with ampacity tables.

Assuming a conductor is properly installed, only the conductor’s size and the ambient temperature have any significant effect on the conductor's ampacity at the termination. Because stranding permits deformation of the cross-section of the conductor, it may have some potential effect, but that is probably overcome by the overall increase in cross-section inside the termination.

What I have highlighted in red is where I believe we are in disagreement. As you mentioned before, we are assuming the conductor's insulation has been removed at the termination. So please provide a reference to anywhere in the NEC where an ampacity is associated with a bare, wire-type conductor...??? As I see it, a uninsulated wire [bare conductor, as NEC defined] has no ampacity rating. This correlates with your stating elsewhere, in effect, a terminal does not have an ampacity rating.

I emphatically disagree that only conductor size and ambient temperature have any significant effect on temperature at the conductor's termination. Understand that I cannot quote your exact words in the preceding sentence because we truly are not affecting the conductor's ampacity.

Jim Dungar mentioned in another thread that the UL termination testing involves the use of 4' of conductor. I am assuming the conductors used for testing are of the typical building types associated with Table 310.16. I further assume they do not simply test with the 4' of conductor suspended in free air or wrapped around the gutter of panelboards under test, but rather use a wiring method or methods installed same as in the field... those which require the use of Table 310.16 for determination of conductor ampacity.

Both Tables 310.16 and 400.5(B) are empirically derived. That is, while there are formulas and factors to adjust them, their original values were determined by measurements based on the worst performing conductor. They also have a healthy built-in safety factor.

I completely agree.

As I stated before, Table 310.15(B)(6) recognizes diversity, Table 310.16 does not. You will also note the values listed in Table 310.15(B)(6) are Ampere ratings, the values listed in Table 310.16 are ampacities. They are not the same thing.

This is correct. The ampere rating is that of the service.

 

[rbalex]

110.14(C) Temperature Limitations. 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.

Ampacity. The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

Of course 110.14(C) can change a conductor?s ampacity ? at the termination. Conductor ampacities aren?t fixed and selecting an ampacity is the Section?s purpose, just like 310.15 (A)(2) directs how to select a conductor?s ampacity in other conditions of use ? not the ?circuit overcurrent rating.? ?Circuit overcurrent rating? isn?t mentioned, or even alluded to, in either Section. In fact, you would be very hard pressed to define or even describe what a ?circuit overcurrent rating? is; but I have no problem whatsoever finding the definition of ampacity. (See above)

From the definition, an ampacity may only be selected when the conductor?s condition of use and temperature rating are known.

So let?s consider Table 310.16 as a basis.

From the Table?s title, the initial ?condition of use? is ??insulated conductors rated 0 Through 2000 Volts, 60?C through 90?C (140?F through 194?F), not more than three current-carrying conductors in raceway, cable, or earth (directly buried), based on ambient temperature of 30?C (86?F).? The various columns indicate the relevant temperature ratings. Therefore, we have sufficient information to select an ampacity from the Table assuming those are the only factors involved.

When other factors are involved, Section 310.15 describes or directs us how to adjust or modify the ampacities under different conditions of use. (Oops ? a circuit conductor?s ampacity can change if it runs through multiple conditions of use.)

Now assume that nothing in Section 310.15 applies; well by golly, for a given conductor temperature rating, the only thing that affects the Table 310.16 ampacities is conductor size and ambient temperature.

Back to 110.14(C), the condition of use is the termination and the ampacities at the terminals are to be based on Table 301.16 conductors with temperature ratings of 60?C or 75?C as appropriate.

 

[Smart $]

I truly do understand your meaning. Yet I see your disposition as fairly adamant toward the present implementation. I cannot contest the present implementation. It is what it is. My disposition, however, is the present implementation is short-sighted in regards to wiring methods which do not determine conductor ampacity under Tables 310.16 or 310.15(B)(6).

You see fault in the present implementation with respect to difering ambient temperatures associated with an installation. I agree, there is fault in this regard.

You would also prefer an engineering solution be permitted under certain conditions of use. I agree this option should be available, with the method of calculation specified (but will likely be rejected on proposal).

My main issue, though, is somewhere between present implementation and the option for an engineering solution. In other words, there are conditions of usage which should permit using a smaller conductor than is presently permitted and without resorting to an engineering solution. In this regard, I feel before we can move onward with such discussion, we will have to agree to premises which are not written in the NEC (the NEC is not an explanatory document so the discussion cannot be limited to within its scope). However, whereever possible, I will attempt to use NEC terminology where appropriate.

In effect, what does 110.14(C) accomplish? I'm of the impression that it is a method to limit the maximum temperature that will be experienced at a conductor termination, so as to ensure the integrity of said termination. Without getting into the how and why, excessively high termination temperature will degrade the integrity of a termination. Do you concur?

Regarding the term ampacity, what does it really mean? Yes the NEC defintion is quite sound for usage of the term within the NEC's scope... but you said yourself a conductor may have several ampacities throughout the length of its run... and I agree. This is why I use the term circuit overcurrent rating. It takes all ampacities throughout the run of the conductor associated with a termination and the termination temperature limitation into account and yields a single value for the circuit which when exceeded constitutes an overcurrent condition.

For the sake of this discussion only, let us define some terms. First, let's use the term "conductor" to infer only insulated, wire-type conductors. Next, let's define the term "conductor ampacity" as the code-determined ampacity of the "conductor" at any point along its run. Lastly, let us define the term "circuit ampacity" as representing the accumulation of all the controlled parameters and requirements imposed thereupon the "conductor", including one or more "conductor ampacity" values.

Please agree or suggest otherwise to the above so we can move on... (of course, that is if you want to )