It was actually CMP 6 that made the comment you cited. You?ll note two other things though: one, while the Panel Statement might be literally true, they made no comment on the technical merit of the actual concept, i.e., that 110.14(C) may be the overall limiting factor and the Exception doesn?t apply in that case; and two, the TCC
did see enough merit to forward it to CMP 1.
With respect to CMP 1, while I agree with the outcome, their Panel Statement was a comedy of errors.
- The Panel Statement: ?The substantiation does not indicate where the present text is unclear?
The Proposal: ?? and needs clarification that these are ampacity and temperature limitations placed on conductors solely at the connections or terminations.?
I didn?t expect to hand-hold so much to point out that, under ?Charlie?s Rule,? the opening sentence states that it is the temperature rating of the conductors that is under consideration. It is still what confuses the general electrical community.
When 110.14(C) was originally introduced in 1993, the general electrical community thought it applied throughout the entire circuit; i.e., only 60C conductors could be used for 100A (14-1AWG) and below circuits unless the terminals were marked 75C and 75C conductors for everything else. 90C conductor ratings were essentially useless, and a few jurisdictions banned them entirely ? the idea being a 90C conductor could somehow always reach 90C no matter what the actual current. (Well, it could of course ? in other conditions of use, but not at the terminations of a proper installation)
It took a Code cycle to add, ?Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.? That helped, but the community was still confused by applying ?Charlie?s Rule? to the first sentence.
It took another Code cycle to recognize NEMA rates all terminals for common LV motors 75C. The first time it was proposed, it was rejected because CMP 1 thought some motors used UL rated terminals. That may be true, but motors aren?t subject to UL listing. This is also an example of a common blind spot for several CMPs (and AHJs) ? the assumption that every thing is, or should be, listed. The ?should be? may be debated; the ?is,? just ain?t so. Look at the first paragraph of 110.14(B) for examples of connections that definitely aren?t.
- The Panel Statement: ?? suggests that equipment terminals or connecting devices have an ?ampacity?, a term limited to conductors.?
Here the problem is that ?equipment terminals or connecting devices? are, in fact,
conductors. In this case,
conductor is not an Art 100 defined term nor is it formally defined elsewhere, so the NFPA Manual of Style (MOS) says we must revert to ?? their ordinarily accepted meanings within the context in which they are used.
Webster?s Collegiate Dictionary, 11th edition, shall be the source for the ordinarily accepted meaning."
Webster?s Collegiate Dictionary, 11th edition:
Conductor ? d (1): a material or object that permits an electric current to flow easily.
Ergo, ?equipment terminals or connecting devices?
do have an
ampacity, it just isn?t determined the same way as wire type conductors and the Art 100 definition makes no distinction.
- The Panel Statement did not address the issue I raised on the affect of ambient temperature on connections. That alone should have gotten an, ?Accept in Principal in Part.?
One reason Table 310.16 ?as appropriately modified by 310.15(B)(6)? is now specifically mentioned (but only since 2002) is that CMP1, under UL influence, wants to limit the applications to the conductor types specifically included in the Table and it doesn?t believe any other Section 310.15(B)[except (6)] requirements need to be addressed - at the terminations. In general, I agree; the exception being that ambient temperature adjustments need to be clearly reaffirmed in 110.14(C).
Before the 2002 addition, I spoke to the author of the original 110.14(C) Proposal. He was uncertain of the ambient temperature?s affect on terminals. I explained that, for all practical purposes, the temperature rise would be degree-for-degree of the ambient temperature?s change from quiescence. The coefficients of thermal and electrical resistivity for heat dissipation purposes could basically be ignored. I also said if the conductor ampacity was determined by 310.16 with no further consideration but the ambient, it would be fine. After some investigation, he agreed and also proposed the change.
The ?appropriate modification? permitted by 310.15(B)(6) is also interesting to note. Here we have 100A plus rated circuits that are always permitted to exceed the 75C and often the 95C rating of conductors ? at the terminals as well. I?m well aware that this is a very limited application; however it is also a tacit recognition that neither conductors nor terminals are seriously affected by moderate overloading.
Since its introduction, 110.14(C) has been significantly revised in every Code cycle ? except 2008. And for reasons that have nothing to do with the Panels? analyses, I?m glad my Proposals didn?t continue the run. Nevertheless, the Section is still flawed ? but my Proposals wouldn?t have corrected everything and would have left room for some serious unintended consequences.
My current concern is the state of ?ambient temperature.? It is both ill defined and poorly applied throughout the NEC. In absence of an ?engineering? solution, it will get worse as the underlying concepts of Section 310.15(B)(2)(c) start expanding; i.e., let someone?s data for a specific installation be expanded to a general application. I?m working with my company?s VP and Chief Engineer, a former ASHRAE President, to create a series of ASHRAE backed Proposals for the 2014 cycle to establish what ?set? of ambient temperatures should be used in various applications.
I may take another crack at 110.14(C) then.
With regard to the 100% rating of the circuits, I didn?t in the first case (500kcmil primary feeder all the way) but did in the second because the tap rules essentially require it ? for any otherwise Code compliant and practical circuit. The second case was a reasonably possible application ? so I analyzed it that way. If you can describe a reasonably practical application for your third hypothesis ? I?ll analyze it too
With regard to your last question, what demands the tap connection to be 60C rated in the first place? (That would have been one of the unintended consequences of my Proposal though) Remember, 110.14(C) does not specify how temperature ratings are to be determined and 110.14(C)(1) doesn?t apply to taps; 110.14 (B) & 110.14(C)(2) do but neither specifiy temperature rating.
BTW what is the temperature rating of that "twist on" wire connector you've been using with 90C conductors?
