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We have electrical service in the house that has a newly updated 200 A service. The service consists of GE PowerMark Gold 200 A 40/80 indoor breaker box model TM4020C80K. Service is provided into the house via underground aluminum wire.

We want to run service from that box back out and underground to a shop that will have a 200 A box in it (as suggested by an electrician).

The plan is to run 1/0 AWG 3 conductor with ground VNTC copper from the house to the shop (about 80 feet).

My question is, what is the best way to connect the shop’s power to the house box? Do I need to find another 200 A breaker for that service?

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    1 - Use aluminum for panel-to-panel feed - no reason to use copper, aluminum is a lot cheaper; 2 - 200A panel (with 200A main breaker as disconnect is fine, but your actual usage will determine the feed size and breaker size. So what is your actual anticipated usage? Feb 15, 2023 at 1:39
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    Just because you are installing a 200 amp panel in the shop doesn't mean to have to supply it with 200 amps. Presumably you are installing a large panel for breaker space. If not, you need to do a load calculation to see how many amps you'll be drawing at the same time. Then size the wiring and breakers appropriately, I have a 200 amp panel in my shop fed by a 100 amp wiring and breaker, I wanted a large panel to allow for expansion when I got new equipment. But very rarely are they used at the same time. I've never tripped the 100 amp breaker feeding the shop panel. Feb 15, 2023 at 2:33
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    If you have need of 200A (or anything near it) at the shop as well as 200A at the house (not just a 200A panel for the spaces and "possible future...") you need a service upgrade to a class 320 meter (400A service, due to different rating schemes for meters and panels.) Your 1/0 copper feeder implies that you're thinking of 150A to the garage, (which would be a lot cheaper on 3/0 aluminum) and that does not leave a lot at the house from 200A. If 90A to the garage would do you (still use a 200A panel) then 2-2-2-4 mobile home feeder (aluminum) is a great price point.
    – Ecnerwal
    Feb 15, 2023 at 2:44
  • What loads do you plan to run in the shop, and how many square feet is it? Feb 15, 2023 at 4:03

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Sanity check

1/0 copper - insane (probably great for the electrician's profit margin, though.) 3/0 Aluminum will carry (slightly) more current at FAR less cost, and the terminals on the breakers and panels are aluminum, so it's very compatible with them. Prepare them properly and torque them properly and don't blow huge wads of cash on nothing useful.

I don't find VNTC "tray cable" rated for burial*, so you need a conduit, so it's nuts (the far milder version of insane) buying cable rather than running individual wires in conduit (much, much easier to pull. Also, you can buy 320 feet of wire with a possible bulk discount .vs. 80 feet of cable. But do shop that rather than assuming. Supplier I just looked at had quadplex 40 cents a foot cheaper.)

*I strongly advise against direct burial anyway - the trench has to be deeper, which costs more, the cable is more exposed to damage, and any savings over buying conduit goes away and then some the second time you have to dig the trench (due to the cable you can't simply pull out getting damaged underground, by rocks, rodents, or whatever.) Trenches are expensive, conduit is cheap.

Then we run into the unanswered questions about your load calculation and use case. But those two seem fairly clear, to begin the sanity checking process, while awaiting more details.

An alternative to "further upgrading your newly upgraded service" depending on the nature of the "shop" and its needs for power is to have a second service provided to it directly. If it's for a business, this makes keeping the business and household expenses separate much easier. It usually costs more per month to have 2 meters, but depending on the price of a service upgrade .vs. a new service drop that might be OK (particularly if it is for a business.)

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    And at that size wire, you can get 320' of one color (a.k.a., any color you want as long as it's black) and mark the ends for neutral (white) and ground (green). Except I would get 400' - because if you measured a few feet off and end up short... Feb 15, 2023 at 3:02
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    Well worth use the nice pulling tape that has foot and/or meter markings on a job this big, to be certain of the length; and then add your fudge factor anyway. 20% is a high fudge factor, but if it's "vaguely 80 feet away that might be more than 100 as the conduit runs" you could still come up short if you don't measure the actual conduit run.
    – Ecnerwal
    Feb 15, 2023 at 3:07
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    Of course if you follow Harper's Law of buying the wire last and count up the sticks of conduit you used then you should know exactly how much wire you need. (But add a few feet anyway. Just because.) Feb 15, 2023 at 3:08
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    There's also the "other thing you gotta check" of would 500 feet as an uncut reel cost less than 320 or 400 feet cut to length? The quick checks I can do with online suppliers don't show that, but your electrical supply house might treat them differently if they don't have to do anything (no measuring or cutting) but ship you a factory reel. Sell the remainder on craigslist.
    – Ecnerwal
    Feb 15, 2023 at 3:11

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