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I am looking at wiring my newly added 12x24 shed. My existing panel on the house is full so I will have to add a subpanel to gain additional spots to feed the shed. The shed is 125 feet away from the house. I will be running a kiln for pottery as well as lights and outlets. The kiln pulls 29 amps. That does not include the extra 20% needed for the extended time the kiln will be running.

Is a 60 amp panel enough for the shed itself? Also what size wire would I use to feed the shed panel for that distance? Also is there a special type of subpanel I should use on the house? Code says I need to have the top of the conduit buried at least 18 inches. Im assuming I need 1-1/4 inch conduit.

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    125 feet is usually not too far, so should get away with 8 gauge for 40 amps needed. The problem with a full panel is you might not have 40 amps to spare, but depends. The best way is to do a load calculation on your panel.
    – crip659
    Commented Feb 19 at 20:46
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    IIUC, you're adding a new panel in the house and running one circuit (actually, you'll need two or more) to the shed. If that's the case, put in a BIG panel. You're already full up - don't limit yourself to a 10-space panel or you'll quickly be full again. A 30 or 40 space panel won't cost much more up front and will save a ton over replacing a small panel with a bigger one in a couple of years. I think you'd need 1 circuit for the kiln, one for lights, and one for other general receptacles. You'd probably want that little 10-space panel in the shed itself.
    – FreeMan
    Commented Feb 19 at 22:06
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    – isherwood
    Commented Feb 21 at 15:17

2 Answers 2

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So, you're not allowed to run multiple circuits to an outbuilding, so that forces you into a feeder and subpanel.

When someone experienced starts pricing subpanel feeder, a surprise emerges: the next size above 30A, sorted by cost, is actually 90A aluminum. Aluminum is proven safe for heavy feeder, despite certain 1970s misadventures involving small 15-20A branch circuits and terminals not rated for aluminum and complete lack of torque screwdrivers.

Thus, we tend to apply 2 AWG aluminum feeder wire like Peter the Great's sword to the Gordian Knot: why think, or scrimp, when you can quantum leap to more than enough? That's what we recommend. Panel lugs are rated for aluminum (typ. made of aluminum), and you need to use a torque wrench on those lugs.

There is no such thing as a 60A panel. All panels are rated 30A, 70A, 100A or larger. (There's no such thing as a 60A feeder either, if you don't believe me, look at Table 310.16 and find where it says "60A" - no wire is that).

Your panel needs be rated >= your feeder size. As freeman discusses in a comment, scrimping on a small panel is not a virtue! Don't bother with that, go ahead and get one with plenty of spaces, and if it's 125A or even 200A, don't worry about it.

If you expect to have more than six hand throws to turn off all the breakers in the subpanel, you will need a main breaker subpanel. Note that if you have two or three single-pole 120V circuits, they can be handle-tied to make them 1 hand throw.

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Harper's answer covers wire sizing quite well. A few additional points:

Subpanel in the House

Often there are ways to squeeze out another two spaces for a subpanel feed. But if not, or if adding a subpanel makes sense for other reasons then:

  • Assuming the main panel is a currently supported common type (e.g., Eaton BR or CH, GE, Siemens, Square D QO or Homeline) then it generally makes sense to get a subpanel of the same product line. That will allow you to move breakers between the panels, which will be helpful initially and could be useful in the future if you have other reasons to rearrange the panels (e.g., relating to generator interlock or other things).
  • If you put the subpanel near the main panel, either next to it or within two feet, then you have some additional flexibility in using conduit between the panels to move circuits around.
  • A review of your main panel is a good idea as often we find problems (wrong breaker types, messed up MWBCs, etc.) which you might as well fix while you're in there.
  • Generally speaking, a straight panel replacement does NOT require upgrading circuits to modern AFCI and/or GFCI requirements. I suspect that a subpanel side-by-side with the main panel with some circuits moved just to make room for the new subpanel feed would keep everything grandfathered. But unless there is specific code regarding that, it may be a AHJ/inspector decision.

Conduit Burial

This actually varies quite a bit by conduit type. See this page and diagram for details:

  • Direct Burial Cable (not recommended) = 24"
  • PVC = 18"
  • Rigid Metal Conduit = 6"

Direct burial cable is generally not recommended because if you have any reason to replace the cable (e.g., damaged or need larger cable) you have to dig again.

It may not be so practical at a long distance like 125', but at least with shorter distances being able to dig 6" deep (to top of conduit) instead of 18" can make quite a difference in the work required.

Subpanel in the Shop

The shop needs a disconnect. That can be:

  • A separate disconnect - don't waste your money
  • Up to 6 breaker throws (Harper described this)
  • A main breaker

Even if you only need a few breakers, a "main panel" can make a lot of sense because it will take care of the disconnect and is often a very good deal, particularly if it is bundled with "bonus breakers".

Ground Rods

You will need either an ufer ground (in concrete) or two ground rods with a wire to the shop subpanel. This is in addition to the ground wire that is going back to the house.

GFCI

A lot will depend on local NEC adoption and local variances, but typically most shop circuits will need GFCI protection. That can be done with a GFCI/breaker (generally more expensive) or, for 120V circuits, with a GFCI/receptacle (generally less expensive - same as most people have in a kitchen or bathroom for the last couple of decades.

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