Derating THHN in 1-1/4" EMT

[imasaltedpretzel]

I have a question about adjustment factors calculations. When using the Adjustment factors table from teh NEC - are the number of conducters assumed to be current conducting? I currently have 9 circuits of mixed 12 gauge/14 gauge THHN. Each has it's own hot, neutral, and ground. If I assume the table refers to only CCC, I am looking at a 70% derate. If the table refers to all conducters in the EMT, I am looking at 45% derate. Since all of these are feeding 15 and 20 amp circuits, the 70 percent derate would mean the work is good to go. 45% derate means I have to make some major changes. Thanks to any help you may be able to provide.

 

[texie]

I have a question about adjustment factors calculations. When using the Adjustment factors table from teh NEC - are the number of conducters assumed to be current conducting? I currently have 9 circuits of mixed 12 gauge/14 gauge THHN. Each has it's own hot, neutral, and ground. If I assume the table refers to only CCC, I am looking at a 70% derate. If the table refers to all conducters in the EMT, I am looking at 45% derate. Since all of these are feeding 15 and 20 amp circuits, the 70 percent derate would mean the work is good to go. 45% derate means I have to make some major changes. Thanks to any help you may be able to provide.

Assuming you have 9 each 120 volt circuits, each with a dedicated neutral, then you have 18 CCC. The adjustment for this would be 50%. For the conduit fill requirements all conductors count including any EGC(s).
If you use #12 (30 amps @90 degree X .5=15 amp) for the 15 amp circuits and #10 (40 amps @ 90 Degree X .5= 20 amp) for the 20 amp circuits you would be compliant.

 

[ceb58]

I have a question about adjustment factors calculations. When using the Adjustment factors table from teh NEC - are the number of conducters assumed to be current conducting? I currently have 9 circuits of mixed 12 gauge/14 gauge THHN. Each has it's own hot, neutral, and ground. If I assume the table refers to only CCC, I am looking at a 70% derate. If the table refers to all conducters in the EMT, I am looking at 45% derate. Since all of these are feeding 15 and 20 amp circuits, the 70 percent derate would mean the work is good to go. 45% derate means I have to make some major changes. Thanks to any help you may be able to provide.

You would not count the EGC's as current carrying conductors. If the neutral is part of a multi-wire branch circuit you would not count it as a CCC also because it would be carrying the unbalanced load.
By what you are saying you have 18 CCC and would have to derate by 50%

 

[roger]

I agree with Texie and CEB but, why do you have an EGC for each circuit?

Roger

 

[infinity]

Shared neutrals as part of a MWBC may or may not count as a CCC depending on a few factors. If the circuits can be arranged so that they do not count then with 9 CCC the #14 and #12 AWG conductors can be used for 15 and 20 amp circuits respectively. This may help:

Neutral Conductors:
Here's some examples of when to count and not count the neutral as a current carrying conductor or CCC:

3?- 208Y/120 or 480Y/277 volt system-different circuit types:
A) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B) 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C) 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B) In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C) In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with an exception, *if the current is more than 50% nonlinear (see below for NEC article 100 definition) then the neutral would count as a CCC.

1?- 120/240 volt system-different circuit types:
D) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E) 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's
Notes:
D) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E) In this circuit the neutral will only carry the imbalance between the two ungrounded conductors so the neutral is not counted as a CCC.
Nonlinear Load. A load where the wave shape of the steady-state current does not follow the wave shape of the applied voltage.
Informational Note: Electronic equipment, electronic/electric-discharge lighting, adjustable-speed drive systems, and similar equipment may be nonlinear loads.