3 CCC's In raceway

[Alwayslearningelec]

I constantly see this in the specs. Ridiculous IMO. Are they worried about derating and having more than 3 CCC in a raceway? They say 3 CIRCUITS that would be more than 3 CCC if counting the neutral(s), no? Thanks.

 

[don_resqcapt19]

Three circuits, each having their own neutral takes you to an 80% ampacity adjustment.

Maybe a very old spec based on 75°C conductors and a 3-phase multiwire branch circuit, giving you only 3 current carrying conductors. With 75°C conductors, even the 80% ampacity adjustment would require you to increase the conductor size or decrease the OCPD rating.

However, assuming circuits with OCPDs of 30 amps or less, and THHN or other 90°C conductors, there is no issue going up to 9 current carrying conductors.

 

[infinity]

They say 3 CIRCUITS that would be more than 3 CCC if counting the neutral(s), no? Thanks.

Yes if there are separate neutrals that would be 6 CCC's for 3 circuits.

 

[charlie b]

However, assuming circuits with OCPDs of 30 amps or less, and THHN or other 90°C conductors, there is no issue going up to 9 current carrying conductors.

Not quite; a common misconception. For a 30 amp circuit with #10 THHN conductors, the limit is 6 CCCs, not 9.

 

[don_resqcapt19]

Not quite; a common misconception. For a 30 amp circuit with #10 THHN conductors, the limit is 6 CCCs, not 9.

240.4(B) would permit the 30 amp OCPD unless the circuit supplies multiple receptacles.

 

[Alwayslearningelec]

Three circuits, each having their own neutral takes you to an 80% ampacity adjustment.

Maybe a very old spec based on 75°C conductors and a 3-phase multiwire branch circuit, giving you only 3 current carrying conductors. With 75°C conductors, even the 80% ampacity adjustment would require you to increase the conductor size or decrease the OCPD rating.

However, assuming circuits with OCPDs of 30 amps or less, and THHN or other 90°C conductors, there is no issue going up to 9 current carrying conductors.

A 3 phase MWBC would require a neutral, that would be 4 ccc, no?

 

[infinity]

A 3 phase MWBC would require a neutral, that would be 4 ccc, no?

No. Unless more that 50% of the load were non-linear (highly unlikely) the neutral in a 4 wire MWBC from a 3 phase Wye system would not be counted as a CCC.

 

[Alwayslearningelec]

Not quite; a common misconception. For a 30 amp circuit with #10 THHN conductors, the limit is 6 CCCs, not 9.

Derating #10's. 90 degree column #10 good for 40A? 80% of 40A = 32A.

 

[infinity]

Derating #10's. 90 degree column #10 good for 40A? 80% of 40A = 32A.

That's correct for 4-6 CCC's (80%). 7-9 CCCs (70%) drops you below 30 amps.

 

[charlie b]

That's correct for 4-6 CCC's (80%). 7-9 CCCs (70%) drops you below 30 amps.

That is why I remember that the "limit" for 30 amp circuits with #10 THHN is 6 CCCs, whereas it is 9 CCCs for 20 amp circuits with #12 THHN.