NEC 310.15(B)(3)(A)

[JasonWrenn]

I have a UPS panel that has been engineered and designed as stated below. My QUESTION is what is the rated amperage of the conductors? The UPS panel is a single 120v feed with neutral. The branch circuits have been designed to leave the panel out of a single 4" aluminum conduit 13 feet long and then enter a cable tray. All the branch circuits are #12 XHHW-2 Multiconductor. So a hot, neutral and ground in each cable. They have 31 circuits leaving the panel through the single raceway. What is the ampacity of the individual #12 wires? TIA

 

[JoeStillman]

You have 64 current carrying conductors in that raceway. The derating factor is 35%. So 25A x 35 % = 8.75A.

 

[jaggedben]

If you are running cables, why put them in a 4" conduit? What type of cables? (What is the outer jacket type?

I think it might be debatable if the conduit is a raceway or a sleeve but the code requirement applies to cables without spacing. Take away the conduit and run compliant cables and you no longer have an issue. Or make it less than 2ft.

 

[JoeStillman]

Would you be able to use a 15A CB under the "next-size-up" rule? There's nothing lower than on table 240.6(A).

 

[Fred B]

2023 NEC 240.6A table now lists 10A as a standard size.

 

[JasonWrenn]

You have 64 current carrying conductors in that raceway. The derating factor is 35%. So 25A x 35 % = 8.75A.

Thank You! Of course I know how to do the math, I'm trying to show other folks here that this installation is incorrect, and I am not leading anyone to my answer. So may I ask how or why you used 25A when XHHW-2 is in the 90c column? TIA

 

[JoeStillman]

Thank You! Of course I know how to do the math, I'm trying to show other folks here that this installation is incorrect, and I am not leading anyone to my answer. So may I ask how or why you used 25A when XHHW-2 is in the 90c column? TIA

You can't use the 90°C column unless you have 90°C terminations, which, as far as I know, don't exist.

 

[Tulsa Electrician]

I deleted my response. Did not read correctly.

 

[Dennis Alwon]

You can't use the 90°C column unless you have 90°C terminations, which, as far as I know, don't exist.

Yes, you can use the 90C column for derating.

(C) Temperature Limitations. The temperature rating associated
with 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. Conductors
with temperature ratings higher than specified for terminations
shall be permitted to be used for ampacity adjustment,
correction, or both.

 

[qcroanoke]

Yes, you can use the 90C column for derating.

I agree.