Using 90°c wire at 90°c ampacity

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NEC 2017 110.14(C)(1)(a)

NEC 2017 110.14(C)(1)(a)

NEC 2017 110.14(C)(1)(a) does not let you use column 90C for circuits rated less than 100A or less, or for wire 14AWG through 1 AWG conductors. This part of the code points out that you must use column 60C
 
palojai said:
NEC 2017 110.14(C)(1)(a) does not let you use column 90C for circuits rated less than 100A or less, or for wire 14AWG through 1 AWG conductors. This part of the code points out that you must use column 60C
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With the exception of NM & SE cable, that is more of an academic rule, than one that will affect what you do in practice. It is common for most modern equipment to be listed and labeled otherwise for 75C. If you do terminate with separate 90C connectors external to your equipment, you can still take credit for the 90C ratings for the run in between the separate connectors.
 
kwired said:
Something I don't think was brought up yet is that if the conductor is operating at 90C it should have higher resistance than same conductor at 75C and insulation won't change a thing.
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The R value in the VD formula comes from Chapter 9 table 8 where the values are calculated at 75°c so what you are say is true, however how often will the wire actually get to 90°c in practical use? It would have to be running continuously at 100% of the ampacity allowed for that wire size (or possibly more if there is reserve built into the table).

When we select wire, it generally has a higher ampacity that we plan on using. We might need a #11 THHN, but select #10 because #11 is not available. #10 has higher ampacity than we need and will never reach it's max operating temperature unless something goes wrong. So when we use a wire based on its 90°c ampacity from the table, in practice in may only reach 75°c thus the result of the standard VD calculation is still correct. Or more precisely, the VD formula almost always predicts a higher VD than will actually occur because the wire is operating at a lower temperature than 75°c.
 
Coppersmith said:
The R value in the VD formula comes from Chapter 9 table 8 where the values are calculated at 75°c so what you are say is true, however how often will the wire actually get to 90°c in practical use? It would have to be running continuously at 100% of the ampacity allowed for that wire size (or possibly more if there is reserve built into the table).

When we select wire, it generally has a higher ampacity that we plan on using. We might need a #11 THHN, but select #10 because #11 is not available. #10 has higher ampacity than we need and will never reach it's max operating temperature unless something goes wrong. So when we use a wire based on its 90°c ampacity from the table, in practice in may only reach 75°c thus the result of the standard VD calculation is still correct. Or more precisely, the VD formula almost always predicts a higher VD than will actually occur because the wire is operating at a lower temperature than 75°c.
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It often won't operate at 90C, but for a given load, using 90C ampacity table will allow smaller conductor size than if using 75C ampacity table - it will operate warmer than if it were a larger conductor if load is same either way.
 
kwired said:
It often won't operate at 90C, but for a given load, using 90C ampacity table will allow smaller conductor size than if using 75C ampacity table - it will operate warmer than if it were a larger conductor if load is same either way.
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I agree.
 
Voltage drop is caused by resistance in the wire. Something that the insulation has no bearing on. Copper although a great conductor has resistance. Silver has a much lower resistance and gold after that. Of the three copper gold silver. Copper is the worst conductor.


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blkmagik21 said:
Voltage drop is caused by resistance in the wire. Something that the insulation has no bearing on. Copper although a great conductor has resistance. Silver has a much lower resistance and gold after that. Of the three copper gold silver. Copper is the worst conductor.
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Not quite. Silver is a better conductor than copper by about 5%, but copper is better than gold by about 30%.

Gold is used to plate conductive contact surfaces because it doesn't oxidize, not for its bulk conductivity.

Also some of the voltage drop in wires is caused by dielectric losses, which insulation certainly does alter. This is not significant for typical inside wiring voltages and operating frequencies, but does matter for things like high voltage transmission lines and high frequency applications.

-Jon
 
electrofelon said:
If we evaluate conductors by weight, aluminum is the best conductor, weighing less than 2/3 of a cooper conductor of the the same resistance.
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I love aluminum wire because it's CHEAP! That makes it the best conductor as far as I'm concerned. :D The light weight also means one less man is needed on a wire pull.
 
I miss the days when copper clad was accepted. Oh wait I’m not that old. But I can imagine if I was, I’d miss those days.


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blkmagik21 said:
I miss the days when copper clad was accepted. Oh wait I’m not that old. But I can imagine if I was, I’d miss those days.


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What exactly is the advantage of CCA as opposed to standard aluminum? I would guess that in concept, the copper would give it a performance advantage, but the NEC doesn't model how you can take credit for that in either ampacity or voltage drop.
 
There's a company in TN now making and pushing CCA ire including Romex.
I sat thru one of the manufacturers dog & pony shows and he goes deep into the metallurgy (binding metals, etc) and the UL testing, etc.
Not sure he will ever overcome the stigma associated with CCA Romex though.

Heres an article (long) for those interested:
https://iaeimagazine.org/magazine/2...for-use-in-residential-branch-circuit-wiring/
 
Copper clad stops the need for de ox that’s one benefit over normal aluminum and it doesn’t break as easy as single strand aluminum does.


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