Here's some examples of when to count the neutral as a CCC:
208Y/120 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*
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 one exception, *if the current is more than 50% nonlinear then the neutral would count as a CCC.
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
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 condcutors so the neutral is not counted as a CCC.
Ok, I have a 20amp 120/208 3 phase circuit. would I keep my 20 amp receptacle and three pole circuit breaker and just jump my MC to #10 instead of 12? will my connectors and devices accept the #10.
If you have all three phases and neutral you only have 3 current carrying conductors, no need to apply ampacity correction for number of current carrying conductors. But even if you ran 10, 8, 6 instead of 12 for any reason, you can still make 12 AWG taps to your devices.Also I will be having a cord from the ceiling receptacle down to a machine, Is it ok to have 30amp devices with a 20 amp circuit breaker .
I am confused over the neutral, it will have an unbalanced load from the three hot legs.
Looks like from table 310.15(B)(3)(a) at 80% I would be at 20amps anyways. without having to derate for ambient at all.
If you have one of each phase per one neutral it will not be imbalanced.
If one phase is carrying nothing then the neutral will carry more but total heat produced in a raceway containing only those four conductors will only create same heat as three conductors, no matter what the balance is.