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what type of wired i need to wire my shop for 120/240 single phase buried about 200' from the house? I plan a 60amp main breaker in the shop. Will 2-2-4 stephens aluminum urd cable be okay?

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    Close. I think you'll need 2-2-2-4 - i.e., 2 for both hots & neutral, 4 for ground. Commented Mar 19, 2021 at 0:53
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    Are you dropping a separate service from your utility service point, or a feeder from a panel either at your pole or in your house? Also, are you still shopping for wire, or were you "gifted" this URD? Commented Mar 19, 2021 at 1:27
  • It will come from the panel in the house. I will probably need to upgrade the house service but right now I just want to have adequate wire in the ground. I am still shopping the wire. Thanks
    – Pat
    Commented Mar 19, 2021 at 1:52

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You'll need 4 wires, no matter what else you choose

The first issue is that your initial choice of cable (2-2-4) was short a wire, as you need to keep neutral and ground separated everywhere downstream of your service disconnect at your house. The good news is that your revised choice (2-2-2-4) has enough wires to get the job done without extra help.

You'll want to run conduit in the ground instead of direct burying the cable, too

The other problem with your plan is that a direct buried cable is rather hard to replace if it breaks or becomes obsolete. Given the cost of PVC conduit, compared to the cost and labor of digging up the cable and replacing it, it's far more economical to lay conduit now so that you don't have to trench again in the future. I would run a 1.5" PVC for the power and a spare 1" PVC, with expansion joints at the stub-ups, as this provides room for running up to 125A(!) to the shop, as well as a network cable or generator feed if you wish it.

Don't sell yourself short on power

While pulling that 2-2-2-4 URD through the PVC will work just fine, expecting a mere 60A from it is selling your cable short as it can handle 80-90A without issue. Furthermore, while you'll need to keep the breaker at the house to an appropriate size for the cable, the "main breaker" at the shed has no such constraint as all it's functioning as is the shed's Code-required local shutoff. Finally, an actual 60A panel is tiny, providing only a few precious spaces for branch breakers, which is a constraint you will rue later on, when the time comes to expand your shop or such.

As a result, I'd put in a 100A or 125A, 24-space or 30-space, main breaker panel at the shed, with a ground bar or two fitted if the panel doesn't come with them from the factory. You'll need to remember to pull the green bonding screw out, of course, and also run an 8AWG or 6AWG copper wire from the panel to a pair of 8' deep rods 6-8' apart. The latter complements your grounding wire by providing the shed with a "shortcut" path for errant natural electricity to get back to Mother Nature, while the grounding wire in the feeder sends wayward utility electricity on an express trip back to the utility's transformer via the main panel neutral bond.

TORQUE ALL LUGS TO SPEC

Last but not least, you'll want to use an inch-pound torque screwdriver or torque wrench to torque all loadcenter and breaker terminal lug connections to the tightening torques marked on the breaker or loadcenter. This is required by 110.14(D) in 2017 and newer editions of the NEC, and is a good idea anyway, as it can keep your electrical system from giving you the loose lugnut!

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Actual load is needed to calculate voltage drop, but at a full 240v 60A load #2 aluminum should be adequate to only experience 3% voltage drop, which is the maximum voltage drop recommended by the NEC for a feeder.

There is some small risk of load imbalance causing a larger voltage loss. If by chance you randomly more than 30A of loads to just one leg your voltage drop could exceed 3%.

You do need 4 wires, two hots, a neutral, and a separate ground for a 120/240v feeder.

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  • Sounds like this wire would get started in the right direction then? Dyke 2-2-2-4 Quadruplex Aluminum URD Cable Direct Burial Wire
    – Pat
    Commented Mar 19, 2021 at 1:53
  • @Pat -- that's a far better choice, yes. Is there a reason you want to direct bury this run instead of laying conduit in the trench? Commented Mar 19, 2021 at 3:43
  • 3% is only a guideline as is 5% at the furthest point both are informational notes in the NEC and not enforceable. If there is 10% drop on occasion the op probably would not notice other than a slightly slow motor spin up.
    – Ed Beal
    Commented Mar 19, 2021 at 15:15
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Conduit is so darned expensive; I'd suggest filling the entire trench with pea gravel. Might be the same money, or a bit more, but expecting to remove the conductors after several years of use may not happen.

Gravel is easy to excavate, and a clear indication that something special is below it. Don't forget the warning ribbon.

And that trench will serve double duty as French drain.

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  • Ah, but the THHN wire that goes into the conduit is so much less expensive than direct burial wire. And, if you ever need to change the wire for any reason, you tie the new to the old and pull. No need to dig, not even with your kid's beach shovel...
    – FreeMan
    Commented Oct 4, 2022 at 11:36

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