jumper
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Thanks. I have probably upsized conductors many times when I did not need to. Oops.
Tap Ampacity
- Thread starter augie47
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Thanks. I have probably upsized conductors many times when I did not need to. Oops.
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- Mission Viejo, CA
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- Professional Electrical Engineer
Let?s go back to my previous example but this time the ambient does enter into the analysis.
The tap is in a design ambient of 30C, the breaker is in an design ambient of 40C. Less than 2.5 ft of the tap conductor are in the 40C ambient.
Ampacities of the #6, 90C tap conductor:
By the NEC Manual of Style the 310.15(B)(2) Ex only applies to 310.15(B)(2) and not to any other Code Section; i.e., it doesn't overrule 110.14(C) - or the laws of physics.
The tap is in a design ambient of 30C, the breaker is in an design ambient of 40C. Less than 2.5 ft of the tap conductor are in the 40C ambient.
Ampacities of the #6, 90C tap conductor:
? At the tap: 75A
? First 22.5 ft of the tap conductor: 75A
? Last 2.5 ft of the Tap conductor: 68A, BUT 75A is permitted by 310.15(B)(2) Ex
HOWEVER,? First 22.5 ft of the tap conductor: 75A
? Last 2.5 ft of the Tap conductor: 68A, BUT 75A is permitted by 310.15(B)(2) Ex
? At the breaker: 57A {65*.88}
Here is where the problem arises. While we are permitted to use the next higher breaker to protect the conductor from overload, the breaker can only accept 57A or less continuous based on 110.14(C).
By the NEC Manual of Style the 310.15(B)(2) Ex only applies to 310.15(B)(2) and not to any other Code Section; i.e., it doesn't overrule 110.14(C) - or the laws of physics.
marti smith
Senior Member
The provisions of 240.4(B) shall not be permitted for tap conductors.
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- Mission Viejo, CA
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- Professional Electrical Engineer
Yeah - thanks for the catch - it doesn't change the analysis.
I'm with you all the way up to "at the breaker". Exactly what is it that you are correcting for ambient temperature... the termination? If you are, you are thereby saying the termination is subject to 310.15 (ambient temperature correction factor location, albeit T310.16 as referenced in 310.15, but changed in NEC 2011 to be in 310.15), and therefore qualifies for the Exception as being a conductor-related ampacity correction and not solely a 110.14(C) matter.
110.14(C) is either a conductor ampacity adjustment or a circuit current limitation. It cannot be both. If the former, it has bearing on the 1/3 tap conductor ampacity stipulation [but then 310.15(A)(2) Exception can be invoked]. If the latter, it does not and we can use, solely, the 310.15 ampacity of the tap conductor (i.e. Table value corrected for condtions of use other than termination temperature limitations).
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Go back and read 110.14(C)(1).
elohr46
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- square one
I know 310.15(A)(2)ex. was always used for when your conduit run went through areas where the ambient temperature was vastly different from one room to the next, didn't know about conduit fill.
Applies any time a conductor has different adjacent ampacities. There is no exclusion clause in the Exception.
You are not getting anywhere...
I'm well aware of 110.14 contents in its entirety.
It amounts to, nothing in the Code says 110.14(C) takes precedence over 310.15(A)(2) Exception (or vice-versa, for that matter).
I can say my ampacity determination is based on the 75?C value of conductor size at the termination. Then I invoke the adjacent ampacities exception and use the higher ampacity of the conductor (90?C) that is immediately adjacent to the termination. I have not changed the determined ampacity of the conductor at the termination (75?C value) to meet the 110.14(C) requirements. The exception simply permits me to use the higher adjacent ampacity (90?C value).
elohr46
Senior Member
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- square one
Yes, I can see how that applies to ambient temp changes, the main reason for that ex. being there in the first place. It's the only example given in the HB.
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- Simi Valley, CA
I'm pretty sure that I agree with Charlie and say that you would have to use the #4.
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- Mission Viejo, CA
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- Professional Electrical Engineer
Yes, I can see that.
It isn?t too surprising though. When 110.14(C) was originally introduced (1993), it created havoc because many jurisdictions thought that the 90C ratings had been rendered useless. While that issue has been basically resolved, it overlooked the reason 110.14(C) was introduced in the first place. It took CMP 1 until 2002 when 110.14(C)(1) was updated to catch on themselves ? and that wasn?t until I convinced the original author there was a problem.
However, before 1993, my interpretation was (and still is) enforceable through 110.3(B) alone.
I sincerely believe that?s true, I just don?t believe you understand its full implications.
As a simple statement that?s also true; however, both 110.14(C) and 310.15(A)(2) requirements must be met and the 310.15(A)(2) Exception only applies to the conductor ? not the terminals
.
Using that logic you could just ignore 110.14(C)(1) anyway and most of 110.14(C) for that matter
Permit me to come at this from a slightly different angle.
Most, although not all, connections and terminations have a thermal (temperature) limit. Whether you would use them or not, there are some connectors that have no metal in them at all ? so they can?t be current carrying; i.e., no ampacity at all. Many connectors that do have metal, have it for mechanical rather than electrical purposes. In any case, the ambient affects the terminal/connector thermally and so does the heat generated by current in the conductor. The temperature of the terminal/connector will rise both with the ambient and the current in the conductor, thus the ?base? temperature rating of the terminal/connector is based on Table 310.16 ampacities and really only needs to be ?corrected? for the ambient.
Please, cast all yout doubts aside. I understand the full implication of the issue. I'm not arguing your implementation (it is actually how I do installations, though this 1/3 tap conductor ampacity issue makes the implementation a bit foggy). I'm arguing that the current NEC wording does not fully support your implementation. That is, it has inconsistencies, or "loopholes".
See... here is one of the loopholes. You believe your implementation to be correct and it very well may be. So much so you don't even see the wording for what it actually states. The wording of the Code just does not say the Exception applies only to wire conductor. In fact, the Exception uses the word "circuit". In fact, nowhere in 310.15(A)(2) in its entirety is the word "conductor", of any type.
Additionally, the NEC only directly defines three types of conductor... bare, covered, and insulated. Any other categorization or type is inferred (or implied, if you must). Is a lug or any other type of terminal a conductor??? The NEC is not explicit on the matter, but we all know it is. Is it part of a circuit??? Without a doubt on my end.
It's not my logic. It is the logic presented [or not, covering the full logic of the matter
hmy:] by the NEC wording we are discussing.I am not arguing the concept. I understand the concept fully. You are wasting your time trying to educate me on the matter. You are assuming I do not fully understand because I am challenging your implementation... but my challenge is based solely on the wording, not the concept itself.
So let's digress just a little...
Let's say we have a 75A breaker, 75?C-rated terminal. Where other conditions of use demand no correction to ampacity, under the current wording in the NEC I can stick a 2" piece of #4 THHN copper in the breaker terminal and do a 90?C-rated splice at the other end to a #6 THHN copper conductor and be compliant. Yes or no?
jumper
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Smart is this pic what you are describing?
Sorta... if you are referring to the last part of my most recent post before this one.Smart is this pic what you are describing?
There is nothing in the NEC that prevents the splice pictured being made in the supply or load panels.
Yes, we knowledgeable know the concept behind 110.14(C) does not permit it. It's just that the current wording of the NEC does not fully support the concept as we understand it.
jumper
Senior Member
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I am not sure I understand? That pic is from a IAEI article that says the set up is legal.
http://www.iaei.org/magazine/2009/0...-about-wire-temperature-ratings-terminations/
http://www.iaei.org/magazine/2009/0...-about-wire-temperature-ratings-terminations/
Actually, that picture is from a Square D article on the subject. I have posted a link to it several times here on the forum(s)... just don't feel like tracking it down right now.
And as pictured, it is fully compliant.
What I'm saying is the current wording of the NEC does not prohibit making the splices depicted in the switch and panel rather than the remote boxes.
jumper
Senior Member
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Got it. Thanks.:thumbsup:
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- Mission Viejo, CA
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- Professional Electrical Engineer
The diagram is fully compliant. Whether it is practical or not, I'll leave up to other's judgment.
There is no loophole, there never was, but since it is a heat transfer rather than electrical issue, most didn't understand it when 110.14(C) was first introduced, and many still don't. In any case, you must comply with both 110.14(C) and 310.15, et al.
"...under the current wording in the NEC".
From 110.14(C)(1)
There is no loophole, there never was, but since it is a heat transfer rather than electrical issue, most didn't understand it when 110.14(C) was first introduced, and many still don't. In any case, you must comply with both 110.14(C) and 310.15, et al.
Yes, assuming the connectors were 90C AND the rest of the panel permits it.
"...under the current wording in the NEC".
From 110.14(C)(1)
Most listed LV equipment still limit any internal connections, including splices to 75C; i.e. 2" may be a bit short and the auxiliary boxes indicated in the diagram may be necessary. Not only that but 110.3(B) still raises its ugly head - so what is the ampacity based on the Art 100 definition; i.e. what is the maximum current permitted.
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