Derating for # of CCC

[mstrlucky74]

If you run a 6 ckt EMT homerun(all 1p-20a for receptacles) from panel and each circuit is required to have separate neutral that would be 12 CCC. 2 questions.
1. Which column would you use from 310.16 75 or 90? I know it's based on terminal ratings but not sure about receptacle terminal ratings. Know they breaker would be 90 degree.
2. Since there would be 13 CCC you would have to reduce ampacity by 50% per 310.15?

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[Dennis Alwon]

Assuming you are using 90C conductors you start at the 90 C column and start the derating. The final ampacity must not be higher than the 75C column.

This is assuming the panel has 75C or 90C terminals

 

[infinity]

For #12 THHN it would be 30 amps * 50% = 15 amp circuits, for #10 THHN it would be 40 amps* 50% = 20 amp circuits.

 

[mstrlucky74]

So you're using the 90-degree column for ampacity. Why?

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[david luchini]

So you're using the 90-degree column for ampacity. Why?

See 110.14(C)

 

[Dennis Alwon]

So you're using the 90-degree column for ampacity. Why?

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Most conductors are rated 90C so you start from there based on the section David mentioned above

Conductors
with temperature ratings higher than specified for terminations
shall be permitted to be used for ampacity adjustment,
correction, or both.

 

[victor.cherkashi]

Recently I put two feeders in one conduit for two outdoor CU, but now I am not sure if I did it correctly.
(2) CU - 3-phase, 31MCA, 50MOP
Each CU fed by 50A circuit breaker.
#8 THWN-2 have to be derated from 55A to 44A (80% - 6 CCC in one conduit)
Question: Can I use 50A circuit breaker for each feeder or the c.b. must be below 44A?

 

[david luchini]

#8 THWN-2 have to be derated from 55A to 44A (80% - 6 CCC in one conduit)

You could have used #10 THWN-2

Question: Can I use 50A circuit breaker for each feeder

Yes

 

[infinity]

Recently I put two feeders in one conduit for two outdoor CU, but now I am not sure if I did it correctly.
(2) CU - 3-phase, 31MCA, 50MOP
Each CU fed by 50A circuit breaker.
#8 THWN-2 have to be derated from 55A to 44A (80% - 6 CCC in one conduit)
Question: Can I use 50A circuit breaker for each feeder or the c.b. must be below 44A?

After the derating the conductors need to be a minimum of 31 amps (forget the OCPD size). As David stated in this application you could have used #10 THWN-2 with an adjusted ampacity of 32 amps (40*80%=32 amps) and the 50 amp OCPD.

 

[kwired]

So you're using the 90-degree column for ampacity. Why?

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You have two things you need to comply with, termination temp rating and insulation temp rating.

For your 20 amp circuits you must have at least 12 AWG conductors for the termination temp rating. But you have no terminations in the raceway so all that matters there is insulation temp rating and the reason you begin adjustments/corrections from 90C ampacity.

But at same time after making adjustments your conductor must still be at least as large as what is required in 75C column (or even 60 C column) for the sake of the termination.

 

[david luchini]

For your 20 amp circuits you must have at least 12 AWG conductors for the termination temp rating.

I would think #14 conductors meet the termination temp rating for 20 Amp circuits.

 

[kwired]

I would think #14 conductors meet the termination temp rating for 20 Amp circuits.

They do and I thought of that when I was replying, 240.4(D) does come into play though.