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I have a pool sub-panel with four #6 AWG running in 1" schedule 40 PVC conduit in ground under the pavers. We are planning on adding some solar panels above pool equipment. I was thinking, instead of tearing up all of our pavers to lay new conduit, to run those four #8 over the same conduit.

My question is, Can I run four #6 and four #8 stranded THWN Wire over 1 inch schedule 40 PVC conduit?


EDIT 1:

I can run the ground wire to the pool sub-panels bus bar and that will eliminate an extra #8 wire over conduit. Would that work? BTW. the pool sub is 40A circuit but it runs #6 wire over 70'. I was trying to use conduit calculator mentioned in the link but it's no longer available. I was thinking of back-feeding the solar to the pool sub (it's 100 amp rated) but I'm facing an issue when (pure sine inverter 8000W) generator is on and it will turn on the solar which is not what I want. My main solar array is interconnected on the service side and shut down when there is power outage. What I want, is to run that little array back to the solar junction box where it would be monitored and manage just like the other panels.

Now that I think about it, I can probably getaway with #10 or even #12 wire for the solar as it's only 4 panels 330w each but microinverters are rated at 240w 240V.

Any suggestions?

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  • The #8 will be limited to 44A, and the #6 will NOW be limited to 60A. Can you live with that? – Harper - Reinstate Monica May 24 at 20:30
  • #6 has a 40A breaker in the mane and #8 would be 20A breaker, so that will totally work for me. At this point, I don't really need to run #8 (I just have about 300FT of each B,R,W,G) and I can run #10 instead. – IgorK May 24 at 20:45
  • Well, you don't need two grounds. That should getcha there. Heck, you don't even need neutral to a solar inverter. Also, since the pool panel is under-powered anyway, why not just terminate the solar at the pool panel? The wire is good for 65A if it's alone. – Harper - Reinstate Monica May 24 at 20:53
  • @Harper-ReinstateMonica, I have a standby generator and my main array is interconnected with the utility company on the service side. If I loose power I need that array to shutdown as well to prevent damage to my generator. – IgorK May 24 at 20:55
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    @ThreePhaseEel, that is correct. – IgorK May 25 at 16:47
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Use 4 6AWG and 3 8AWG, since you don't need more than one grounding wire

Your 1" Schedule 40 PVC provides 214mm² of usable area in your situation. The existing 6AWG wires take up 130.84mm² of fill, leaving 83.16mm² of fill available for the new feeder. This is enough room for 3 8AWG wires (two hots and one neutral) at 70.83mm² of additional fill, as both feeders can share the same equipment grounding conductor, although going up to 6AWG for the solar feeder would be way too much at 98.13mm² of fill.

With that, you have to do an 80% derate from the 90°C ampacities of the conductors in question, which puts you at 60A for the 6AWG and 44A for the 8AWG, or 40A, practically speaking, which is enough for quite a sizeable solar array (7.6kW, to be precise, since you have to derate again for continuous power through the breaker).

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  • That would work for me perfectly as the #6 is on 40A beaker and #8 is on 20A. – IgorK May 28 at 18:29
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TL;DR No.

Chart in answer at: How do I determine the fill rating of a conduit?

  • 1" Schedule 40 @ 40% = 0.333 in2
  • 8 AWG = 0.0366 in2 x 4 = 0.1464 in2
  • 6 AWG = 0.0507 in2 x 4 = 0.2028 in2
  • 0.1464 + 0.2028 = 0.3492 > 0.333

There may be additional issues of how many circuits and/or types of circuits in the same conduit. But 0.3492 > 0.333 so it doesn't matter.

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    But if the "4 8 AWG" include a grounding wire, they don't need to, as the pool is (presumably) already grounded, and that puts it back in the realm of "just possible, but the pull will be an [expletive deleted!]" since the grounding wire can be shared. – Ecnerwal May 24 at 17:41
  • @Ecnerwal Good point, though an additional complication would be that the grounds would have to connect together in the pool panel, while as described the solar wires are just passing through the conduit and might not be entering the pool panel at all. – manassehkatz-Moving 2 Codidact May 24 at 17:45
  • Actually, it'll work. You don't need two ground wires and that can be #10 anyway (no hope of running >60A given the 310.15(B)(3)(a) derate). Also 1" trade size is slightly larger than 1", it's like 1.050. – Harper - Reinstate Monica May 24 at 20:28
  • So, If I run 4x #6 and 3x # 10, while connecting the ground in the pool sub, it should work/it will be legal? – IgorK May 24 at 20:39

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