Tap Conductor Temperature

[iwire]

Look at 240.21

That answers the question

No it does not answer the question.

 

[erickench]

That part I disagree with. I believe it only pertains to direct contact, not indirect.

Nonetheless there is metal-to-metal contact from the 500MCM to the tap to the OCPD device. There is heat conductivity throughout the whole circuit. NEC 110.14(C) clearly specifies that a conductor to conductor connection as well as equipment must be sized to the lowest temperature rating.

 

[erickench]

Smart $ here's a quote from that technical brief that you posted:

Remember that a conductor has two ends, and that the termination on each
end must be considered when applying the sizing rules. For example,
consider a conductor wired to a 75 ?C termination on a circuit breaker at one
end, and a 60 ?C termination on a receptacle at the other end. This circuit
must be wired with a conductor that has an insulation rating of at least 75 ?C
(due to the circuit breaker) and sized based on the ampacity of 60 ?C (due to
the receptacle).

Interesting.

 

[Johnmcca]

"For example, consider a conductor wired to a 75 ?C termination on a circuit breaker at one end, and a 60 ?C termination on a receptacle at the other end."

But that does not cover the feeder in question. If it is sized to the 60C ampacity and connected to a 75C is it not appropriatley sized for the temperature. The conductors will not necessarily approach the max temp.

 

[Smart $]

Smart $ here's a quote from that technical brief that you posted:

Remember that a conductor has two ends, and that the termination on each
end must be considered when applying the sizing rules. For example,
consider a conductor wired to a 75 ?C termination on a circuit breaker at one
end, and a 60 ?C termination on a receptacle at the other end. This circuit
must be wired with a conductor that has an insulation rating of at least 75 ?C
(due to the circuit breaker) and sized based on the ampacity of 60 ?C (due to
the receptacle).

Interesting.

Yes it is. Especially when it seems to contradict itself by supporting the terminal box method of transitioning to another rating.

 

[Smart $]

"For example, consider a conductor wired to a 75 ?C termination on a circuit breaker at one end, and a 60 ?C termination on a receptacle at the other end."

But that does not cover the feeder in question. If it is sized to the 60C ampacity and connected to a 75C is it not appropriatley sized for the temperature. The conductors will not necessarily approach the max temp.

But the feeder is connected to the tap. It is sized to the 75?C ampacity for its size, not the 60?C ampacity.

Granted the conductor will likely not operate continuously at the maximum permitted temperature... but the application of the code requirements is not laxed for this consideration.

 

[Smart $]

Smart $ here's a quote from that technical brief that you posted:

Remember that a conductor has two ends, and that the termination on each
end must be considered when applying the sizing rules. For example,
consider a conductor wired to a 75 ?C termination on a circuit breaker at one
end, and a 60 ?C termination on a receptacle at the other end. This circuit
must be wired with a conductor that has an insulation rating of at least 75 ?C
(due to the circuit breaker) and sized based on the ampacity of 60 ?C (due to
the receptacle).

Interesting.

PS: The code doesn't actually say this, i.e. the insulation rating must be of the higher termination temperature rating. It is again someones interpretation. Until it is so noted in an official interpretation document, readily available to those that practice the method, it remains nothing more than speculation.

 

[erickench]

If we were to use the 75' insulation for the tap we might be able to get away with 75' ampacity for the feeder since the operating temperature at that ampacity would not degrade the tap insulation through heat conductivity from metal-to-metal contact. But of course the tap must be sized to 60' ampacity.

 

[iMuse97]

Eric, thanks for continuing the discussion.

 

[Johnmcca]

I think 110.14 (C) (1) agrees with Eric' interpretations.

 

[rbalex]

Okay, here's a doozie of a question for you guys. Let suppose you had a 500 MCM feeder rated at 380A at 75'C and you wanted to run a tap that terminates to a 100A overcurrent device. Now the temperature for this OCPD is not given so you would have to apply either NEC 110.14(C)(1)(a) or (b) which states that equipment terminations rated at 100A or less shall have the connecting conductors rated 60'C otherwise it's 75'C. What temperature would you use to size the tap? 60'C or 75'C? I mean the OCPD is rated at 100A but the feeder is rated at 75'C.

The problem is the first sentence of 110.14(C) is poorly worded; but the underlying physics should not be an issue - and I would expect a PE to understand the physics no matter how poorly the text is written.

First, 110.14(C) should read: 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.

Why? Because Ampacity is an Article 100 defined term and, when it is used properly in context, it is not the temperature rating of the conductor but its ampacity that is to be determined in 110.14(C)

Art 100

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

A single insulated conductor may have many “conditions of use” and therefore many different ampacities throughout its length. We are told in 310.15(A)(2) that the “condition of use” that creates the lowest ampacity must be used throughout the entire conductor length. The 310.15(A)(2) FPN also reminds us that connecting and terminating conductors is also a “condition of use” that must be considered and directs us to 110.14(C).

The basic rules in 110.14(C) are generally extracted from UL and are summarized in the White Book under Category Code AALZ. These rules are based on conductors in Table 310.16 and only as they apply to relevant equipment.

Sections 110.14(C)(1)(a)(1)&(2) essentially tell us that, in absence of markings to the contrary, terminations of circuits rated 100A or less or marked for #14 to #1AWG create a “condition of use”, as if the conductor were only rated 60C. NOTE: This “condition of use” applies only to the termination. Section 110.14(C)(1)(a)(3) recognizes “markings to the contrary” and Section 110.14(C)(1)(a)(4) recognizes motor terminations are not subject to UL and have a 75C NEMA rating. NOTE AGAIN. Since conductors usually have two termini, the motor terminals may be 75C but the other end may still be 60C.

Section 110.14(C)(b) similarly addresses terminations above 100A or #1AWG.

In addition, Section 110.14(C)(2) cautions that certain connections are specifically marked with maximum ampacities associated with specific conductor temperature ratings.

NOTE: There are often cases where other “conditions of use” (e.g., underground duct banks) are more restrictive than the terminations.

The FPN notes that other documented restrictions may exist.

Terminations for conductors in Tables 310.67 to 310.86 are 90C unless otherwise marked. See 110.40.

In short – For the OP, use the 60C rating.

P.S.- I am well aware that 310.15(A)(2) has an exception. It is irrelevant to the discussion, so lets not get into gnat straining and camel swallowing.

 

[Smart $]

...
First, 110.14(C) should read: 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.

Why? Because Ampacity is an Article 100 defined term and, when it is used properly in context, it is not the temperature rating of the conductor but its ampacity that is to be determined in 110.14(C).[/FONT]

I meant to write something similar but got sidetracked :roll:

I agree... 100% with what you changed, but not 100% with the entire sentence. The only part I feel is still lacking is the "connected" clause. Does "any connected termination, conductor, or device" mean only items in physical contact with the metal of the conductor, i.e. directly connected ...or does it mean all items connected, including indirectly connected, such as a lug and breaker or just the lug?

....

In short – For the OP, use the 60C rating.

But the big question you did not answer.

What of the feeder and its rating? ...And if the tap is permitted under the conditions provided, how so? Please cite reference(s).

P.S.- I am well aware that 310.15(A)(2) has an exception. It is irrelevant to the discussion, so lets not get into gnat straining and camel swallowing.

Where in all tarnation did that wit come from? Was it floating around in the back of your mind just waiting for an opportunity to get out?

 

[rbalex]

I agree... 100% with what you changed, but not 100% with the entire sentence. The only part I feel is still lacking is the "connected" clause. Does "any connected termination, conductor, or device" mean only items in physical contact with the metal of the conductor, i.e. directly connected ...or does it mean all items connected, including indirectly I meant to write something similar but got sidetracked :roll:connected, such as a lug and breaker or just the lug?
...

Granted, the ambiguity of English might permit either interpretation if the sentence had no context - but it does. That is, the subject of Section 110.14 is Electrical Connections. To me, that suggests the sentence means a current carrying contact, not mere proximity. As I also noted, 110.14(C)(2) and the FPN cautions that other conditions may also limit the ampacity, but when they exist they are provided with specific documentatation or markings.

...
But the big question you did not answer.

What of the feeder and its rating? ...And if the tap is permitted under the conditions provided, how so? Please cite reference(s).
...

The physics would suggest the feeder could use the 75C ampacity as its starting value when determining its various ?conditions of use.?

What about the tap connection? Indeed, what about it? From the source to the tap connection there is no reason not to use the calculated or tabulated 75C ampacity. Beyond the tap the current is reduced anyway.

At the tap? Assuming both conductors are properly sized for the ambient at the tap?s location, the ?cold leg? of the feeder beyond the tap will act as a sink since it will be operating with a significantly lower current. Will it be sufficient to lower the connection?s temperature to accommodate the 60C conductor? Yes, because all three conductors actually act as sinks. In fact, assuming the 380A load is reduced to 300A beyond the tap (380-100*.8) the ?cold leg? it is operating below the 60C rating of a 500kcmil conductor anyway.

What if we used a 90C conductor on the feeder? Come on, you still won't be permitted to use over 380A or tap it in a location where it would exceed 75C without a concurrent reduction of the 60C conductor's ampacity.

Is the tap otherwise legal? That would depend on which tap rule one applies. The OP does not specify sufficient details, but the most likely candidate within the parameters given would be 240.21(B)(5).

...
Where in all tarnation did that wit come from? Was it floating around in the back of your mind just waiting for an opportunity to get out?

I suppose I should have cited site the real Source ? Matthew 23:24. It was preemptive of the excessively legalistic approach we ocassionaly observe.

 

[ohmhead]

Well question what about by example dual rated wire ?

 

[hardworkingstiff]

I know I have maintained the position your installation as proposed would not be permitted... but that is mostly influenced by the general consensus I have gotten from this(these) forum(s). However, as I said above, I know a proper "tap" can be made, leaving the NEC validity aside.

For instance, there are those that believe a 75?C circuit can be transformed to a 90? circuit and back by installing two terminal boxes in the run where all wires and terminations are rated 90?C. Square D even includes this possibility in one of their technical briefs.

...and a slightly modified (by me) diagram...

This brings a question to my mind. What is the minimum length of 75C rated conductor need to be before you change to the 90C rated conductor (using the SQ D example)? 2', 3', 4', 10', 2" ?

 

[Smart $]

Granted, the ambiguity of English might permit either interpretation if the sentence had no context - but it does. That is, the subject of Section 110.14 is Electrical Connections. To me, that suggests the sentence means a current carrying contact, not mere proximity...

IMO, I don't believe the subject line is enough, as it uses the plural of the word "connection", which is made more unclear with the "any connected" clause. Granted, a single continuous conductor will always have two connections to be a part of a circuit. But there is no text which distinguishes the connection of a conductor to a lug and that lug to its device (especially, but not limited to, when the lug is part of a manufactured assembly) as each being a separate connection where the latter is or is not subject to this termination temperature rating requirement.

What about the tap connection? Indeed, what about it? From the source to the tap connection there is no reason not to use the calculated or tabulated 75C ampacity. Beyond the tap the current is reduced anyway.

At the tap? Assuming both conductors are properly sized for the ambient at the tap?s location, the ?cold leg? of the feeder beyond the tap will act as a sink since it will be operating with a significantly lower current. Will it be sufficient to lower the connection?s temperature to accommodate the 60C conductor? Yes, because all three conductors actually act as sinks. In fact, assuming the 380A load is reduced to 300A beyond the tap (380-100*.8) the ?cold leg? it is operating below the 60C rating of a 500kcmil conductor anyway.

What if we used a 90C conductor on the feeder? Come on, you still won't be permitted to use over 380A or tap it in a location where it would exceed 75C without a concurrent reduction of the 60C conductor's ampacity.

Counterpoint: Let's say the feeder ends with multiple taps. Continuing with the example, 380A on a 500kcmil conductor with 75? terminations, the feeder ends at the location of the 100A tap where another tap is made sized for 280A and 75? terminations?300kcmil Cu. Since there are no provisions for to do engineering-level evaluations of temperature at the "junction", under the NEC and when operating at maximum current we must assume the 500 and 300 kcmil conductors are operating at a temperature of 75?. Therefore, the 100A 75?/60? tap conductor would be the heat sink. So at what point along the conductors is the temperature below 60???? There is no means provided for such a determination.

Is the tap otherwise legal? That would depend on which tap rule one applies. The OP does not specify sufficient details, but the most likely candidate within the parameters given would be 240.21(B)(5).

I don't see how the tap rules apply to the concept we are discussing, as they are essentially a max conductor distance without overcurrent protection rule... not a minimum distance for transition to a different temperature rating rule.

I suppose I should have cited site the real Source ? Matthew 23:24. It was preemptive of the excessively legalistic approach we ocassionaly observe.

Ahhh!!! Woe to the hypocrite.

 

[Smart $]

This brings a question to my mind. What is the minimum length of 75C rated conductor need to be before you change to the 90C rated conductor (using the SQ D example)? 2', 3', 4', 10', 2" ?

I can't answer that question with any specificity. The NEC has no provisions for such a determination.

Jim Dungar once (or more?) mentioned something to the effect that UL tests termination temperature with conductors out to 10 feet as I recall.

 

[rbalex]

...

Ahhh!!! Woe to the hypocrite.

OUCH! ? Honest I do try to avoid legalism. In the context of the NEC it?s difficult to avoid though since both the laws of physics and laws of men come into play. Thankfully, also in the NEC context, the laws of men tend to be more restrictive so both can be observed.

Within common rules of interpretation and within context ?Electrical Connections? would apply to a single connection as well as to multiple connections ? have a real lawyer explain that to you.

Oddly enough, I disagree with the Square D example you posted elsewhere because equipment is also an Article 100 defined term. While 110.14(C) is a general statement, 110.14(C)(1) kicks in with any connection to equipment. In absence of any specific NEC provisions to the contrary, the lug itself is equipment. It may, in fact, reduce the ampacity of a 90C conductor to that of a 60C or 75C conductor if is marked with a conductor size.

The most compelling counter argument to my position, is Erik?s in the post you were responding to. As I said my original post though, we are not trying to determine the temperature rating, but the ampacity of the conductors. Otherwise we would be forced to only use 60C conductors for 100A (14-1 AWG) circuits and 75C for everything else, 110.14(C)(1)(a)(2) and 110.14(C)(1)(b)(2) notwithstanding; 90C coinductors would be useless.

At the time of this post I?m being called to a outside meeting ? I?ll deal with your counter example later.

 

[Smart $]

OUCH! ? Honest I do try to avoid legalism. In the context of the NEC it?s difficult to avoid though since both the laws of physics and laws of men come into play. Thankfully, also in the NEC context, the laws of men tend to be more restrictive so both can be observed.

My comment wasn't meant to incite an explanation of your philosophy.

I was simply noting that some circles quaintly refer to the scripture you cited as "Woe to the hypocrite".

Within common rules of interpretation and within context ?Electrical Connections? would apply to a single connection as well as to multiple connections ? have a real lawyer explain that to you.

No need for a lawyer's explanation... I already understand. The prblem actually stems from such understanding in that it can apply to a single connection as well as multiple ones. So the question remains, does it apply to only the physical connection at each end of the conductor, or does it include what is connected to the connector and other subsequent connections. If the latter, at what point does the "connection" end. Under this premise, you could technically go all the way back to the Service Point, because it is conductors, equipment, and their [inter-]connection that permit the power to reach the utiliztion equipment.

IMO, though unenforcable, the FPN after 110.14(C)(2) implies that subsequent connections do affect the coordination of conductor ampacity and terminal temperature ratings, and vice-versa.

Oddly enough, I disagree with the Square D example you posted elsewhere because equipment is also an Article 100 defined term. While 110.14(C) is a general statement, 110.14(C)(1) kicks in with any connection to equipment. In absence of any specific NEC provisions to the contrary, the lug itself is equipment. It may, in fact, reduce the ampacity of a 90C conductor to that of a 60C or 75C conductor if is marked with a conductor size.

I agree with the physics of the Square D example. Yet I also agree that the current wording of the NEC does not permit such an installation.

The most compelling counter argument to my position, is Erik?s in the post you were responding to. As I said my original post though, we are not trying to determine the temperature rating, but the ampacity of the conductors. Otherwise we would be forced to only use 60C conductors for 100A (14-1 AWG) circuits and 75C for everything else, 110.14(C)(1)(a)(2) and 110.14(C)(1)(b)(2) notwithstanding; 90C coinductors would be useless.

If you think Eric's post is the most compelling counter argument, you're confusing me on what your position is on the matter.

At the time of this post I?m being called to a outside meeting ? I?ll deal with your counter example later.

I'll be waiting.

 

[rbalex]

I apologize for not getting back to this sooner; but real life can interfere with forum activities occasionally.

In addition, I wanted to add content from an actual set of Proposals I made for the 2008 cycle. Both were rejected, which turned out to be the right intermediate outcome, but for the wrong reasons. The Proposals were made for the right reasons, but I just didn?t have the will to fight at the Comment stage.

Oddly enough, the 310.15(A)(2) Proposal would appear to put me on the opposite side of our current discussion. I was at the time. The original Proposal was written in 2005 and sat on the back burner for a few years. The CMP Statements did give me time to rethink my position through.

That being said, lets consider the case where there are dual taps at feeder terminus; one 75C, 300A and the other, the original 60C, 100A. We must assume, for the sake of discussion that all other Code requirements are met or the installation would be invalid for reasons not associated with 110.14(C)(1).

Within that assumption, we must assert that both taps are still required to meet 240.21(B). So, as I said before, which tap rules apply? The underlying purpose of 240.21(B), is to establish reasonable overload protection for the taps specifically, as opposed to overcurrent protection (which also includes short-circuit and ground-fault) for them in general. For a wire conductor, an overload OCPD can be located anywhere between the conductor?s source and its load. For short-circuit and ground-fault the OCPD must be between the source and the conductor or, in the case of a feeder tap, between the feeder and its source. Alternately, the load may not be subject to overloading and only short-circuit and ground-fault protection are needed.

Within context of the OP, I already said 240.21(B)(5) is the only tap rule that could be applied, otherwise it would be invalid tap and a 110.14(C)(1) violation is purely academic.

Which tap rule(s) could reasonably apply to the 75C, 300A tap? With the possible exception of 240.21(B)(1), any applicable tap rule would still ultimately limit the continuous current to 80% (240A); in which case, the primary feeder would only carry 300A continuously ? again well below the 60C rating.

Well what about 240.21(B)(1)? I concede it could be a problem ? I just can?t imagine a reasonable design where it applies under the conditions we?re discussing.