NEC 110.14(C) Temp Rating

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cdcengineer

Senior Member
Is there any reason why 110.14(C) prohibits the connection by either splice or lug of a 75?C & 90?C conductor? The example in question is connecting a #2 AWG THWN-2 to a #3 AWG THWN conductor. The circuit is protected by a 110A fuse and the fuse terminal rating is 75?C. The issue here is that they already ran 1000's of feet of #3.

Input is greatly appreciated.
 

kingpb

Senior Member
I agree with Don.

It just means you can't operate the conductor over the current that would make the conductor temperature rise above 75 deg C. That is the reason for the different current columns in the Tables of 310.
 

mull982

Senior Member
I have heard of others using a 90deg cable for the cable run and then splicing a small piece of 75deg rated cable onto the end of the cable for terminating on a breaker rated for a 75deg C. Even if this is done, wont the small piece of 75deg rated cable be the limiting factor in the cable run (no matter how small) and thus make the whole cable applicable to the 75deg C column of 310.16?
 

jim dungar

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Location
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I have heard of others using a 90deg cable for the cable run and then splicing a small piece of 75deg rated cable onto the end of the cable for terminating on a breaker rated for a 75deg C. Even if this is done, wont the small piece of 75deg rated cable be the limiting factor in the cable run (no matter how small) and thus make the whole cable applicable to the 75deg C column of 310.16?
Only if they are the same physical size conductors. There is no issue if the ampacity of the 75?C is greater than that of the 90? one.
 

cdcengineer

Senior Member
Yes- it makes the whole cable only cable of carrying the current of the 75?C column ampacity. Is that your question? In my case, ampacity isn't the issue. The issue is rating of temp of cable landed on the terminal which is 75?C. Per 110.14, I think we can land only the minimum rated cable on that terminal unless we are using a higher temp cable for ampacity adjustment or correction (such as ambient temperature, or more than 3-current carrying conductors in a raceway, etc.) which in this case is not a factor.

That's my interpretation.
 

Smart $

Esteemed Member
Location
Ohio
Your OP says the #2 is THWN-2, which is the 90?C rated conductor.

...and the #3 is THWN, which is a 75?C rated conductor.

Sounds backwards ;)


What we really need to know is the load current...
 

Smart $

Esteemed Member
Location
Ohio
Explanation: We need to know because #3 THWN is only rated for 100A, and you said adjustment and correction is not a factor. You cannot protect a 100A-rated conductor with a 110A fuse under the 240.4(B) next standard size rule because 100A fuse is a standard rating.

PS: Is this regarding the PV installation of one of your other threads?
 
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cdcengineer

Senior Member
It is backwards. The #2 is THWN and the #3 is THWN-2. And yes, it's the same project. The contractor brought me in late after they had run lots of wire and conduit because the utility wanted some over-sight.
 

Smart $

Esteemed Member
Location
Ohio
It is backwards. The #2 is THWN and the #3 is THWN-2. And yes, it's the same project. The contractor brought me in late after they had run lots of wire and conduit because the utility wanted some over-sight.
Sounds better.

One additional thing needs pointed out, and that is the splicing or transition terminations must be made using 90?C or better equipment and as I understand it, the transition cannot be done in the same enclosure as 75?C-rated equipment.
 

cdcengineer

Senior Member
I'm envisioning a N-3R junction box with ILSCO (or equal lugs). The only thing in the box rated 75C is the #2 wire and I don't believe that violates 110.14.
Thx
 

Smart $

Esteemed Member
Location
Ohio

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
So, is the #3 in the middle of the run and not terminated to any terminals rated 75C. If that is the case I think you are good to go.
 

Dennis Alwon

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Sounds better.

One additional thing needs pointed out, and that is the splicing or transition terminations must be made using 90?C or better equipment and as I understand it, the transition cannot be done in the same enclosure as 75?C-rated equipment.
Smart- not doubting you but where is this info. If you are not connecting to the other equipment what difference does it make?
 

jim dungar

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Engineer
There is no restriction on where the junction of the 75? to 90?C conductor occurs.

In fact, there is not even a definitive minimum length of 75?C required, although I like to use 4' because that is the length that UL uses when doing tests on breakers.
 

cdcengineer

Senior Member
Similar crimp connectors were considered, but they are rated to 90C and that (IMO) would not meet the intent of 110.14. We have a j-box 15' above the inverter where they'll make the transition.

I believe I failed to note this earlier. Our continuous current (PV System 690.8) is 102.375. I think Smart $ requested this, but I missed it.
 
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rbalex

Moderator
Staff member
Not disagreeing with anyone here, but I believe this is the relevant citation, such as it is, for Smart's comment. From the 2010 UL Whitebook,
ELECTRICAL EQUIPMENT FOR USE IN ORDINARY LOCATIONS (AALZ):
Distribution and Control Equipment Terminations:
?
A 75 or 90?C temperature marking on a terminal (e.g., AL7, CU7AL, AL7CU or AL9, CU9AL, AL9CU) does not in itself indicate that 75 or 90 ? C insulated wires can be used unless the equipment in which the terminals are installed is marked for 75 or 90?C.
Higher temperature rated conductors than specified may be used if the size is based on the above statements.
Category Code AALZ is more or less the ?Super Category? for all UL listed products. (It was a lot clearer in 2004 and earlier, but references in other Category Codes will usually reference you back to AALZ eventually).
Technically, not only must terminals be marked for 75 or 90?C, but the entire Distribution and Control Equipment assembly must be too. If you look carefully at all the various labels, stickers and attached instruction, they probably will be ? but this is not an absolute statement by any means.
 

Smart $

Esteemed Member
Location
Ohio
Not disagreeing with anyone here, but I believe this is the relevant citation, such as it is, for Smart's comment. From the 2010 UL Whitebook,
ELECTRICAL EQUIPMENT FOR USE IN ORDINARY LOCATIONS (AALZ):
Distribution and Control Equipment Terminations:
?
A 75 or 90?C temperature marking on a terminal (e.g., AL7, CU7AL, AL7CU or AL9, CU9AL, AL9CU) does not in itself indicate that 75 or 90 ? C insulated wires can be used unless the equipment in which the terminals are installed is marked for 75 or 90?C.Higher temperature rated conductors than specified may be used if the size is based on the above statements.
Category Code AALZ is more or less the ?Super Category? for all UL listed products. (It was a lot clearer in 2004 and earlier, but references in other Category Codes will usually reference you back to AALZ eventually).
Technically, not only must terminals be marked for 75 or 90?C, but the entire Distribution and Control Equipment assembly must be too. If you look carefully at all the various labels, stickers and attached instruction, they probably will be ? but this is not an absolute statement by any means.
Regarding the highlighting of your UL category quote, I made the statement...

...the splicing or transition terminations must be made using 90?C or better equipment and as I understand it, the transition cannot be done in the same enclosure as 75?C-rated equipment.
It seems to me that I covered what the UL statement says... :confused::roll:

Does that not cover the "Distribution and Control Equipment assembly"...???
 

Smart $

Esteemed Member
Location
Ohio
Similar crimp connectors were considered, but they are rated to 90C and that (IMO) would not meet the intent of 110.14.
If the crimp/compression reducing splice connectors are rated 90?C, how does that not meet the intent of 110.14(C)... especially (C)(2).

... We have a j-box 15' above the inverter where they'll make the transition.

I believe I failed to note this earlier. Our continuous current (PV System 690.8) is 102.375. I think Smart $ requested this, but I missed it.
Thanks.... I was curious mostly before you clarified that the #3 was the THWN-2 conductors, and the #2 was THWN.
 
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