3 Phase SE Conductors

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Little Bill

Little Bill

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I had an inspector say that 4/0 cu was required for the SE conductors up the mast for a 200A 3Ø service. I've always used 3/0, which is good for 200A. He didn't actually talk to me but to the owner. The only thing I can think of is he is thinking the conductors need to be derated since there would be more than 3 CCC conductors in the mast/raceway. But I don't think the neutral would count as a CCC.
Thoughts?
 
Little Bill said:
I had an inspector say that 4/0 cu was required for the SE conductors up the mast for a 200A 3Ø service. I've always used 3/0, which is good for 200A. He didn't actually talk to me but to the owner. The only thing I can think of is he is thinking the conductors need to be derated since there would be more than 3 CCC conductors in the mast/raceway. But I don't think the neutral would count as a CCC.
Thoughts?
Click to expand...

Is it routed in thermal insulation? See 338.10(B)(4), which specifies the 60C ampacity overriding 75C as you'd ordinarily use for this wiring method.

It is rare that neutral on a circuit of all phases would count as a CCC. That concern applies for harmonic-intensive loads, where triplen harmonics specifically add up rather than cancel on the neutral. If the loads are mostly linear, regardless of the balancing, neutral need not count as a CCC.
 
A bit out of my league, but for the sake of helping out and possibly learning something myself, I'll chime in.
I've always seen and done 3-0 for 200A services and NEVER seen or had it questioned by any inspector.

There's this from Mike Holt on EC&M (scroll down to "Neutral Conductor):

"The neutral conductor of a 3-wire single-phase 120/240V system, or 4-wire 3-phase 120/208V or 277/408V wye-connected system isn’t considered a current-carrying conductor.

The neutral conductor of a 3-wire circuit from a 4-wire 3-phase 120/208V or 277V/480V wye-connected system is considered a current-carrying conductor...

The neutral conductor of a 4-wire 3-phase circuit is considered a current-carrying conductor where the major portion of the neutral load consists of nonlinear loads. This is because harmonic currents will be present in the neutral conductor, even if the loads on each of the 3 phases are balanced."

www.ecmweb.com/national-electrical-code/article/20888271/top-50-nec-rules
 
Carultch said:
Is it routed in thermal insulation? See 338.10(B)(4), which specifies the 60C ampacity overriding 75C as you'd ordinarily use for this wiring method.

It is rare that neutral on a circuit of all phases would count as a CCC. That concern applies for harmonic-intensive loads, where triplen harmonics specifically add up rather than cancel on the neutral. If the loads are mostly linear, regardless of the balancing, neutral need not count as a CCC.
Click to expand...
There would be no insulation surrounding a mast going up the side of a building. The conductors would be THWN and wouldn't be subject to the requirement for using the 60 deg column. Perhaps I should have said "service entrance" instead of SE, which leads one to think the conductors are treated like NM cables.
 
Carultch said:
Is it routed in thermal insulation? See 338.10(B)(4), which specifies the 60C ampacity overriding 75C as you'd ordinarily use for this wiring method.
Click to expand...
That's true for the 2014 NEC, but was amended in the 2017 NEC to only apply to SE cable "with ungrounded conductor sizes 10 AWG and smaller."

Cheers, Wayne
 
I agree with Larry he's definitely incorrect. #3/0 is rated for 200 amps at 75 degrees C. The neutral would not count as a CCC.
 
Must be the global warming correction.

Seriously: I believe the inspector is wrong unless there are additional unstated circumstances, eg. heat from a different source, reason that 60C limitation is in play, kickback from the CDA, etc.

-Jon
 
wwhitney said:
That's true for the 2014 NEC, but was amended in the 2017 NEC to only apply to SE cable "with ungrounded conductor sizes 10 AWG and smaller."
Click to expand...
I was unaware of this until @Carultch brought it up. 2014 already applies to SE cable only. It also only applies to Branch Circuits and Feeders. A Service Drop is not considered a Feeder as far as I'm aware.

The "10 AWG and smaller" portion may be an amendment in 2017 (I'm still catching up on '17 and '20)... but '14 does indeed limit it to SE Cable only as well as Branch Circuits and Feeders only.
 
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