Derating question

[Alwayslearningelec]

Have several 3P 30A motor circuits. They have 3 #10 hots, 1 #10N and 1 #10G.

If I were to combine two of these circuits in one pipe I would be limited to 70% of the ampacity listed in the 90 degree column?

So using THHN @ 90 degrees #8 is good for 55A. I would have to take 70% of that which is about 38A. So I could use #8's? Thanks

 

[infinity]

A 3 phase motor does not require a neutral. If you had two circuits in a single raceway that would be 6 CCC'S.

 

[Dennis Alwon]

What is the actual draw of the motor-- What voltage etc.

 

[Alwayslearningelec]

A 3 phase motor does not require a neutral. If you had two circuits in a single raceway that would be 6 CCC'S.

The panel schedule calls for a neutral.

 

[infinity]

The panel schedule calls for a neutral.

It wouldn't change anything as far as the number of CCC's, you would still only have 6.

 

[Alwayslearningelec]

It wouldn't change anything as far as the number of CCC's, you would still only have 6.

So even if a motor has a neutral it's not a ccc? I thought you always count the neutral as a ccc?

 

[infinity]

So even if a motor has a neutral it's not a ccc? I thought you always count the neutral as a ccc?

A 3Ø motor does not have a neutral regardless of what the panel schedule says. In general the neutral for a 3Ø MWBC is never counted as a CCC.

 

[Alwayslearningelec]

A 3Ø motor does not have a neutral regardless of what the panel schedule says. In general the neutral for a 3Ø MWBC is never counted as a CCC.

So a 3 phase motor circuit is considered MWBC?

 

[Dsg319]

So a 3 phase motor circuit is considered MWBC?

No. No three phase motor ever requires a neutral. He’s saying even with the panel schedule showing it,it will not be used so no need to count it. And a neutral in a MWBC is not considered CCC as the three circuits will cancel each other (not sure if that’s the best term) but regardless the neutral will only ever carry the unbalanced current

 

[infinity]

So a 3 phase motor circuit is considered MWBC?

No, but you've stated that the panel schedule says to run four conductors so it's a 4-wire MWBC where the neutral is not being used nor is it needed.

 

[Dennis Alwon]

I have never seen a 3 phase motor with a neutral but is it possible there is some type of electronics in this motor that may require a neutral? I remember some old Amana a/c units, single phase but 240V that did require a neutral. Could it be something like that?

 

[Alwayslearningelec]

I have never seen a 3 phase motor with a neutral but is it possible there is some type of electronics in this motor that may require a neutral? I remember some old Amana a/c units, single phase but 240V that did require a neutral. Could it be something like that?

They are AC units, condensers and unit heaters

 

[retirede]

They are AC units, condensers and unit heaters

An AC circuit is not (always) simply a motor circuit. Calling it a motor circuit in the first post sent this thread down a rabbit hole.

 

[Knightryder12]

They are AC units, condensers and unit heaters

I have recently done a project where the condensing unit of a 5 ton mini-split system (480V, 3 phase) that required a neutral because the ECM motor for the fan was 277V. It was Daikin unit.

 

[Dennis Alwon]

I have recently done a project where the condensing unit of a 5 ton mini-split system (480V, 3 phase) that required a neutral because the ECM motor for the fan was 277V. It was Daikin unit.

If that is the case then the neutral would be counted, I believe

 

[infinity]

I have recently done a project where the condensing unit of a 5 ton mini-split system (480V, 3 phase) that required a neutral because the ECM motor for the fan was 277V. It was Daikin unit.

They do exist. I had seen similar units where the neutral was required as you've mentioned due to the 277 fan voltage. When we went back and inquired they told us that the unit had been ordered that way by mistake as it was the only unit in a 42 story building that needed a neutral.

 

[augie47]

Assuming the neutral is needed and we now have 8 cccs would the derated amapcity need to be equal or greater than the MCA or some other value ??

 

[wwhitney]

If that is the case then the neutral would be counted, I believe

No, still no need to count the neutral. An MWBC/feeder with both 3 phase 3-wire loads and L-N loads (all of one type, so not with varying phase shifts on different legs) will still have current cancellation in the neutral.

Cheers, Wayne

 

[wwhitney]

Assuming the neutral is needed and we now have 8 cccs

Except we wouldn't.

would the derated amapcity need to be equal or greater than the MCA or some other value ??

Yes, the derated value is the ampacity, and MCA is minimum ampacity.

Cheers, Wayne

 

[don_resqcapt19]

A 3Ø motor does not have a neutral

I wired one 500 hp 480 volt 3 phase motor that had a T0 connection point. We did not connect anything to it, and no one could tell me why that motor had a TO connection point.