NEC interpretation issue 1

[aeffects]

I want to know if my interpretation of 110.14(C) is correct.

Can I use the 75°C column ampacities for all gauges? (given the fact that I use 75°C or 90°C insulation and my terminals allow for 75°C wires)

I'm 99% certain that I can, but I want to make sure.
I've seen a lot of devices that allow the use of 75°C wires (especially breakers), and this would prove very useful for feeders.

Thanks in advance.

 

[DRWeig]

Yes, as long as EVERYTHING in the path is listed or labeled for 75°C use -- AND as long as the ambient temperature does not exceed 30°C (86°F).

Based on NEC 2011 110.14(C) and table 310.15(B)(16).

That's my opinion! Your AHJ's opinion (as well as your local code) may vary.

Good on ya,

Goober Dave

 

[dpc]

Maybe. It will depend on the type of wiring method being used - this is covered in the NEC Article for each wiring method.

You also have to be aware of the terminations at the other end of the feeder - and any terminations in between.

Also, the circuit breaker rating is based on use of a certain range of wire sizes being used - this is part of the UL rating. So this (minimum requirement must be met regardless of the NEC.

We use 60 deg C rating for all feeders on 100 A circuits and smaller, regardless. Saves a lot of worry.

David Castor

http://www.cvoes.com

 

[DRWeig]

Thanks for more clarity, David.

aeffects: dpc is much more fluent in this area than I am, your question has many more facets than it seems on the surface.

I would also vote for sticking with 60°C wire for under-100A circuits. Lots less iffy.

Good on y'all,

Goober Dave

 

[wareagle]

DPC

We use 60 deg C rating for all feeders on 100 A circuits and smaller, regardless. Saves a lot of worry.

It may save worry but cost more $. There is no reason not to use the 75C rating for the conductors listed in 310.16 if the equipment terminals are listed for 75C. You can also use the 90C rating for derating the cable for temperature and number of conductors in conduits. Romex conductor is only listed for 60C.

 

[rbulsara]

What dpc said and that is what I do too. Any perceived savings by doing otherwise is not worth the trouble or risk, especially when you are the specifying engineer.



Rafiq Bulsara

http://www.srengineersct.com

 

[wareagle]

rbulsara
What kind of risk would you be concerned with?

 

[rbulsara]

Not getting 75 deg C rated equipment/terminals, especially rated less than 100A, despite specifying so. NEC has taken pains to explain that.

Rafiq Bulsara

http://www.srengineersct.com

 

[wareagle]

I can see where that would be a big concern. It was my understanding that the new equipment was all rated for 75C.

 

[dpc]

Panelboards and circuit breakers are generally rated for 75 deg wire these days, but when the other end of the wire goes to an heat pump package from Taiwan,a welding receptacle, or God only knows what, THAT end may very well only be rated for 60 deg C. Then you could end up with one 50A circuit taken a different conductor size than the 50 A circuit right next to it. It increases the risk of getting the wrong size wire pulled in, especially on Monday morning or Friday afternoon.

My recommended approach is conservative, I'll agree with that.



David Castor

http://www.cvoes.com

 

[wareagle]

Under those conditions, I agree also.

 

[aeffects]

I agree with you all, I do not intend to use 75C rating for branch circuits, maybe for some feeder circuits I will, but mostly wanted to make sure that I was getting things rigth.

Thank you all for your answers .

 

[sspeare]

Here is what I believe the NEC requires:

1. If the device rating is under 100 Amps, and the temperature rating is NOT marked, you have to select Ampacity based on 60 degrees C.

2. Most equipment, even if under 100 Amps, is listed for 75 degrees C, so you use the 75 degree C column in the Article 310 Tables.

3. The Ampacity of NM sheathed cable, also known as "Romex", is always based on 60 degrees C.

--> I'm writing this from memory alone, and not citing NEC sections. Somebody please jump on me if I'm wrong.

 

[jghrist]

You can use the 90°C column for Type NM for derating purposes if the resulting ampacity doesn't exceed the 60°C column value. Essentially, you assume that Romex will be terminated on 60°C terminals.