De-rating MC with 4 conductors??

[Kurt Vilary]

310.15(B)(3)(a)(4)
Adjustment factors shall not apply to Type AC cable or to
Type MC cable under the following conditions:
a. The cables do not have an overall outer jacket.
b. Each cable has not more than three current-carrying
conductors.
c. The conductors are 12 AWG copper.
d. Not more than 20 current-carrying conductors are
installed without maintaining spacing, are stacked, or
are supported on “bridle rings.”

Thanks for your help Lucky. That is what I was looking for. But, as I continued reading...

310.15(B)(5)(a) Neutral Conductor
A neutral conductor that carries only the unbalanced
current from other conductors of the same circuit shall not be
required to be counted when applying the provisions of 310.15(B)(3)(a).

I interpret that to mean we are compliant using 12/4 or 10/4 as a home run for 2 separate 120v circuits (2 hots+2 neutrals) with out derating as per 310.15(B)(3).

Correct???
KV

 

[ActionDave]

Thanks for your help Lucky. That is what I was looking for. But, as I continued reading...

310.15(B)(5)(a) Neutral Conductor
A neutral conductor that carries only the unbalanced
current from other conductors of the same circuit shall not be
required to be counted when applying the provisions of 310.15(B)(3)(a).

I interpret that to mean we are compliant using 12/4 or 10/4 as a home run for 2 separate 120v circuits (2 hots+2 neutrals) with out derating as per 310.15(B)(3).

Correct???
KV

No, not correct. You are compliant, but not for reason you think. When you have individual neutrals for each hot you count the neutral as a Current Carrying Conductor, when you share a neutral you do not.

It's not usually a problem using a 30A breaker or 20A for 10AWG and 12AWG respectively because of the small conductor rule in 240.4(D) and TABLE 310.15(B)(3)(a) only makes you derate 80% with nine or less CCC in a MC cable and you don't bundle more than twenty of them up. It starts to suck when you are running conduit or using larger conductors.

 

[infinity]

Thanks for your help Lucky. That is what I was looking for. But, as I continued reading...

310.15(B)(5)(a) Neutral Conductor
A neutral conductor that carries only the unbalanced
current from other conductors of the same circuit shall not be
required to be counted when applying the provisions of 310.15(B)(3)(a).

I interpret that to mean we are compliant using 12/4 or 10/4 as a home run for 2 separate 120v circuits (2 hots+2 neutrals) with out derating as per 310.15(B)(3).

Correct???
KV

As Dave mentioned neutrals are CCC's in a two wire circuit and other times they may or may not be CCC's depending one some other factors. 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.

 

[darekelec]

De-rating is nowadays called 'applying adjustment factors'.

Welcome to the forum Kurt:thumbsup:

 

[Kurt Vilary]

Got it. Your explanation makes it crystal clear. Thanks for your detailed help.