Derating conductors in raceway

[Hoodood]

I have an 1 1/4" conduit with 9 120 volt 20 amp circuits which totals 18 conductors. I have to derate the conductors so do the neutrals count as current carrying? If they count then I need to derate 50% for 10 - 20 current carrying conductors or can I use the 70% for 7 - 9 conductors. Thanks in advance.

 

[infinity]

Since each circuit is a two wire circuit both conductors count as CCC's so use 18 in your calculation.

 

[kwired]

Nine circuits eighteen conductors - sounds like one neutral for each ungrounded conductor - none of the neutrals are carrying the imbalance current of multiple ungrounded conductors so that means every conductor is current carrying - eighteen total. 50% ampacity adjustment is necessary.

If you had three phase wye with nine ungrounded three grounded (three multiwire branch circuits), then those neutrals would be non current carrying as they only carry unbalanced current of the associated grounded conductors, and you would be able to go with 80% ampacity adjustment for nine conductors.

 

[infinity]

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:

3Ø- 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.

1Ø- 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.

RobertMeier2017

 

[Hoodood]

Thanks to all for simplifying this!