Neutral Conductor

[Jimmy7]

If you install two 20 amp 120v circuits in conduit that originate from a 120/240 volt service, is that two or four current carrying conductors?

 

[roger]

If you're talking about two 2 wire circuits you have 4 CCC's, if you're asking about a MWBC odds are you have 3 CCC's

 

[tom baker]

2 neutrals, 2 hot?
Edit Roger beat me to answer

 

[LarryFine]

if you're asking about a MWBC odds are you have 3 CCC's

Wouldn't a 1ph MWBC be more likely to have two CCCs?

 

[Jimmy7]

2 neutrals, 2 hot?
Edit Roger beat me to answer

Two hots and two neutrals

 

[LarryFine]

Two hots and two neutrals

Definitely four CCCs.

 

[Jimmy7]

In this case, there would be four current carrying conductors that would need to be derated by 80%. #12 copper at 90 degrees is 30 amps.
30amp x 80% = 24 amps. Correct?

 

[roger]

Be sure you're starting with a 90 deg conductor and your right

 

[roger]

Wouldn't a 1ph MWBC be more likely to have two CCCs?

Doh! You're right Larry.

 

[Carultch]

If you install two 20 amp 120v circuits in conduit that originate from a 120/240 volt service, is that two or four current carrying conductors?

Since the neutral conductors are a mandatory part of the return path for the current, and always must carry the full current, the neutrals have to count as CCC's.

Neutral only "doesn't count", when it's possible for the ungrounded conductors to carry the current of a balanced condition back on their own, with the neutral carrying zero current. The neutral is on standby, waiting for a load imbalance. If you compare the total heating (proportional to current^2) for just the ungrounded conductors, and compare it to what it would be for any possible unbalanced situation, you'll see that the neutral never generates any new heat, that wasn't there in the balanced situation.

This is why for multiple hots and the one neutral on a feeder, you're only required to count the hots as CCS's and not the neutral. But two 1-pole circuits sharing a conduit, each with their own neutral, requires you to count all 4 conductors.

 

[Jimmy7]

Be sure you're starting with a 90 deg conductor and your right

If it’s 75 deg wire go off the 75 degree column to derate?

 

[roger]

If it’s 75 deg wire go off the 75 degree column to derate?

Yes. You start your calculation beginning with the conductors starting temp.