Please check my PVC-size calculation

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LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Grittins. I'm wiring a 24kw genny and a 200a ATS at a house that has a 150a MB panel inside that should have had an outside main, but didn't, so I have to separate the neutrals and grounds. Oh, joy! The meter base is already a 200a one, and I'll be using 4/0 SER, so I'm calling it an upgrade so the POCO won't apply any charges for their work.

My question is about the genny feeder. It's only about 12', so I'll use individual copper conductors in PVC and run it outside the foundation instead of through the crawl space. The genny has a 100a breaker, so I plan to use three #3 wires and a #8 EGC. According to my conduit-fill calc, as soon as I add one #14, it bumps the PVC from 1" to 1-1/4".

The genny requires six control wires, so, my question is whether the calculator (http://www.electrician2.com/rveltrain05/rf_calculator.html) is correct, and would I be better off running a 1" and a 1/2" PVC or a single 1-1-4" PVC? I would check using the NEC numbers, but frankly, I'm too sick today to concentrate enough to do the math.

Thank you in advance for any responses.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
The calculator to which I linked above says three #3 THWN-2 wires have an area of 0.0973 for a total of 0.2919 sq.in.

The single #8 has 0.0366, which brings the total up to 0.3285 sq.in., and the PVC has an allowable area of 0.333 sq.in.

Thus, it's saying that there is a remaining area of only 0.0045 sq.in., and adding even one #14 takes it over 40% fill.

Are those numbers wrong? I'm confused. It seems that adding the control wires shouldn't make that much difference.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
In some cases you need a separate conduit for the control circuit. It depends on he genset
Generac used to require separate raceways from a box on a whip, but they changed it some years ago.

The last genny I did, I ran the control wires in a separate 1/2" LNFC because I used SER for the feeder.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Generac used to require separate raceways from a box on a whip, but they changed it some years ago.

The last genny I did, I ran the control wires in a separate 1/2" LNFC because I used SER for the feeder.


Yeah, I knew about generac but I didn't know if they were all like that.... I would also run a separate conduit for the controls. Keeps it simple for me that way....
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
The genny most likely has two KOs, one for power and one for control. I would run two conduits. Last one I did I ran 1-1/4" and 3/4".
 
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