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I am using 2-1/2" schedule 80 electrical conduit because it is being run along/under my property's dirt access road. From the research I have done and reading fill charts it looks like I can use either schedule 40 or 80 in 2-1/2". I just want to make sure it will meet requirements for fill without any question. Or, do I really need schedule 80?

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According to table C.9 referenced in this answer, 2-1/2" Schedule 80 can handle up to 5 x 4/0 conductors, so you're fine even for a full hot/hot/neutral/ground (and ground definitely doesn't need to be as big).

Actually, it isn't exactly like that. 4/0-4/0-4/0-2/0 cable probably takes a bit more than the individual wires, but is relatively round (which helps) and I found plenty of references to running it through 2" conduit, so 2-1/2" gives you a little more room to work with.

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    Excellent. Thank you for the feed back. I am only running 4/0 4/0 2/0.
    – Dean
    May 19, 2021 at 20:16
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    @Dean Pardon my asking, but are you just running 220 V? I assume your not running a neutral.
    – tnknepp
    May 19, 2021 at 20:19
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    @tnknepp Generally speaking, you are correct. The only catch is there might be some downsizing allowed on the neutral once you hit a certain size, based on the usage normally being at least somewhat balanced. But I don't know the specifics on that. But since OP stated "transformer", this is likely hot/hot/ground, with neutral provided as transformer center-tap at the destination. May 19, 2021 at 21:47
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    I spoke with the lead inspector at the L&I. I explained to him that my electrician said I needed 4/0 all same size. He told me they do not require the neutral to but upsized. So, 4/0 4/0 2/0. The 2/0 is neutral. No ground needed coming from Transformer to Meter/panel combo. But 2 ground rods at panel.
    – Dean
    May 20, 2021 at 2:06
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    PUD is running their wire from what they called a distribution box at the road to a Transformer they are installing on my property. From transformer it is my responsibility to run wire to my meter/panel. They said they are little different, where the wire from transformer to meter/panel is owner responsibility. Even the PUD said 4/0 4/0 2/0, but because they follow their own rules it was suggested I ask a licensed electrician. I asked the electrician I am mostly consulting with and he said 4/0 4/0 4/0. I asked L&I who has to buy it off and they said they do not require up size on neutral.
    – Dean
    May 20, 2021 at 2:48

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