Derating for multiple conductors "There and Back"

[Jason Spray]

I am working on solar project for a Multi-tenant building where the meters are all grouped together on the end of the building. We need to run (2) hots, & (1) neutral wire and the EG to the utility meter, and then back to the tenant panel. There is ONE existing conduit that goes from the panel to the meters. If we run the wires "there and back" in the same conduit, we would need (7) wires total, (2) hots & (1) neutral out, & (2) hots and (1) neutral back, that makes (6), plus a single EG that makes (7).

Do I have to derate for (6) current carrying conductors if it's the same circuit going "there and back"?

 

[infinity]

Unless this part of a 3 phase WYE system the neutrals are not considered CCC's. That still doesn't change anything because you still have 4 CCC's and need to apply the 80% derating factor.

 

[Jason Spray]

Unless this part of a 3 phase WYE system the neutrals are not considered CCC's. That still doesn't change anything because you still have 4 CCC's and need to apply the 80% derating factor.

It's single phase 240 with the neutral.
I thought you always had to include a neutral as a CCC.
But anyhow, you answered my question. I wasn't sure, since it's the same circuit, if they were counted twice (there and back).
Thank you for your response Infinty!

 

[jumper]

It's single phase 240 with the neutral.
I thought you always had to include a neutral as a CCC.
But anyhow, you answered my question. I wasn't sure, since it's the same circuit, if they were counted twice (there and back).
Thank you for your response Infinty!

Nope. Here is quote from Infinity from another thread. Very useful.

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.

 

[Jason Spray]

Great information. Thank you!

 

[drcampbell]

... Do I have to derate for (6) current carrying conductors if it's the same circuit going "there and back"? ...

Ampacity and derating are based on how much heat is produced by I²R losses, how much heat can be dissipated, and how high a temperature the insulation can tolerate. Where the current's going to -- or returning from -- is irrelevant.

 

[Smart $]

Do I have to derate for (6) current carrying conductors if it's the same circuit going "there and back"?

Consider any number of dead-end switch legs in the same conduit. For each switch, a hot goes to the the switch and the switched leg returns... same circuit. The conduit has 2 CCC for each switch. To paraphrase drcampbell, the source of the current is irrelevant.