Is correct this math 3 ckts120V(6ccc)?

[marcosgue]

Let's do this:
-Scenario 1.
3/4" emt conduit: 3 circuits #12awg 120V+G (6ccc)
More than 3ccc adjustment factor 80%
#12awg (30A----90°column)
30A*0.8=24A
I'm still good with 20A ocpd each circuit
-Scenario 2.
3/4" emt conduit: 3 circuits #10awg
120V +G (6ccc)
80% adjustment factor
#10awg (40A-----90°column)
40A*0.8=32A
I'm still good with 20A ocpd each circuit
In this cases:
1. For derating adjustment factor is correct to use 90° column ampacity?
2. The neutral conductor qualify as ccc?
Thanks all in advance

 

[winnie]

If you have a separate neutral for each circuit, then it counts as a CCC and your calculations of conductors are correct.

If you use a wire with 90C insulation (most but not all types have this) then you are correct to derate using the 90C column.

 

[marcosgue]

Those conductors area typically thhn insulation using in commercial facilities.
Can you guide me where and when the neutral conductor don't have to be count as ccc? Thanks

 

[infinity]

Those conductors area typically thhn insulation using in commercial facilities.
Can you guide me where and when the neutral conductor don't have to be count as ccc? Thanks

Take a look here:

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.

 

[marcosgue]

For derating adjustment factor for more than 3 ccc purposes we've always using 90° ampacity column in table 310.16?

 

[winnie]

For derating adjustment factor for more than 3 ccc purposes we've always using 90° ampacity column in table 310.16?

For typical THHN in typical dry conditions, yes.

Again: you can find exceptions, but you need to look for them. An example is wire that is rated THHN/THWN in conduit in a slab foundation. This would force the 75C column because it is considered a wet location. But these days typical conductors are THHN/THWN2 (rated for 90C wet).