Power to Detached Pole Barn

[TDKPE]

Minimum aluminium conductor size for 100A is 1/0. That's using the 60C column. The 75C column allows 100A on 1-gauge. Since it's conduit, and assuming individual conductors, and since it's underground for part of the run (considered a 'wet' location), you'll be using THWN most likely, and that 75C rating is acceptable as long as the lugs on both ends are also 75C rated, which they should be.

Voltage drop with 1-gauge at 100A is about 7.5V, assuming all of it is through one hot and the neutral only. Half that if 100A from each leg, as the neutral carries nothing then.

Voltage drop with 1/0 is 6V at 100A on one leg only.

It's highly unlikely you'll ever draw 100A on one leg only, if you balance the 120V circuits reasonably well. And the NEC doesn't require a max voltage drop - it's in the fine print notes (fpn's), which are informational only, and not code enforceable.

For 80A, 1-gauge at 60C or 2-gauge at 75C is ok.

And you can't run loose conductors in the rafters - has to be in conduit, or in a cable tray. I would use schedule 40 PVC indoors, but 80 outdoors (required where it comes out of the ground, due to damage exposure), or just sch. 80 everywhere.

[TDKPE]

I don't think so. URD doesn't have an outer sheath, but it is suitable for wet locations and for use in conduit or direct burial. It's intended as service cable, up to the meter, not as service entrance cable. And I don't believe the insulation is rated for indoors.

You need #6 minimum for the grounding conductor at 100A. Probably cheapest to buy THWN of the desired gauge for both current-carrying and grounding conductors. Doesn't need to be color coded at that size (but do mark the ends).

[TDKPE]

#6 aluminium and #8 copper equipment grounding conductors are good to 100A per Table 250-95. If you upsize the phase conductors for voltage drop compensation, the grounding conductor also has to be upsized, but that doesn't sound like the case here.

Per Table 250-66, service conductors of 1/0 or smaller require #8 copper grounding electrode conductor, with no splice at the first grounding electrode (rod) in the chain. And bare is typical.

[MauleSkinner]

All ya really need is one 20-amp fuse, provided you switch the lights, air conditioner, table saw, and dust collector on in that order!


No...I'm not advocating that...I did that for a couple of months until I got my garage rewired.

[crokett™]

Do you actually need 100A at your pole barn? I'm asking because I built a shop and ran electrical nearly as far as you were proposing. I used 2-2-2-4 aluminum which was both cheaper and easier to work with than 1/0. Although I did have to derate to 90A that was about twice as much as my worst case power draw was going to be.