I'm putting a 50' run of feeder from a main to 100A sub panel. This will be buried in sched. 40 PVC conduit. I plan to pull 1/0 Al for the hot/hot/neutral and 4 awg Al ground. Should I be using XHHW, THWN, or type USE if I plan to pull individual wires in the conduit? I see that type USE has a thicker jacket which requires a conduit upsize.
2 Answers
Any of them are fine.
Don't go thinking it's clever to push the conduit fill limits. Those will make for a tougher pull. Nothing sucks more than having to call an electrician to finish your job solely for their truck full of exotic and costly pulling tools. So doing things that makes your pull easy is always preferred.
Speaking of that, a 100A feeder only needs #1AL wire. All those wires you named are allowed 75C thermal, and the panels and terminals are rated 75C so you're all set. And #6Al ground with the #1. Your 1/0 could be upsized to 120A in the future, so there's that.
answered Jun 17, 2023 at 19:54
Harper - Reinstate MonicaHarper - Reinstate Monica
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Given the choice, XHHW is very slightly smaller diameter than THWN, and it's also slightly tougher. It is also generally more flexible.
You are planning to run schedule 40, but you generally need some schedule 80 conduit where the conduit run exits the ground and becomes "exposed to damage" unless it never does (entering a basement below ground, say) so you generally need to size the wire fill for schedule 80, not the slightly larger hole, due to thinner walls, of schedule 40.
If you only contemplate running 100A 50 feet the wire size is more than you need, (and nets you a whopping 0.43 volts on 100A, or 0.34V on the 80A you should be planning for with a 100A breaker over using 1 AWG) for the extra expense, at but you'll need minimum 1-1/2" PVC (for three 1 AWG and one 6 AWG or for three 1/0 and one 4 AWG) if any part of the run is exposed to damage and thus needs schedule 80, even if parts of the run are schedule 40.
2" conduit for a fill percentage considerably lower would be well worth considering, as it gives an easier pull.
Two useful calculators, or pick your own. No affiliation other than I use them myself. Read the instructions to get accurate results.
http://conduitfillcalculator.com
You could use RMC or IMC with the conduit acting as the ground conductor in 1-1/4" size for either size wires. If you don't cross a driveway that can greatly reduce your burial depth requirement (aka how deep the trench is) which is a case where you can spend money to save other money, sometimes.
