Bring electriticy to the shed


Old 03-27-16, 03:42 PM
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Bring electriticy to the shed

In my backyard is an underground rmc conduit containing 4 wire (10 AWG) with 30 amp service for a hot tub the previous owners never built. It must be 30 years old. It is stubbed to a wet location junction box 6" above grade.

I want to run buried threaded conduit beneath some brick steps to a shed about 20 feet away from the stub.

My initial thought is to dig 8" and run 2x3/4" threaded conduit to the exterior of the shed, splice 10AWG thwn in a new larger wet location junction box and place a small breaker panel in a NEMA 3 enclosure at the shed wall. (second conduit is for the inevitable request for additional lighting in the vicinity of the current junction box once my wife see lights in the shed).

30 amps is plenty for the shed (lights, 120V receptacles for light duty table saw and light duty router table)

My questions:

1. Is the overall plan reasonable?
2. Do I need to place a grounding rod at the shed, which is 30' from the house, or simply treat the new panel as any other subpanel?

thanks for your help.
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Old 03-27-16, 04:04 PM
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Welcome to the forums! Your plan is reasonable with certain caveats. You can use the box for a junction as it is already protected with a breaker at the house. You will need to have a subpanel in the shed and separate your grounding wires and neutral wires on separate busses with the neutral isolated from the casing. You will need to dig a minimum of 18" for your conduit, and could more easily use pvc conduit rather than threaded rigid. There would be no benefit to using the steel pipe and pvc would last longer.
Old 03-27-16, 06:51 PM
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Metal conduit is not recommended for underground use as it will corrode and eventually break a hole through or completely break off.
PVC is also easier to use.

If you can somehow run the conduit above ground, then you can avoid digging the ground. Otherwise, you have to dig 18". If there is 2" concrete over the trench or have GFCI protection on the circuit it can be 12" (6" with GFCI protection).
If 4" or thicker concrete above the trench, it can be 4". Under the driveway is 18" regardless of concrete thickness (for one or two family dwelling).

If you rent a trencher, 18" is no big deal, but if you try to dig with shovel, it won't be easy.

I don't know what size junction box is already there, but 4 10AWG wire should be able to splice in most junction box. So, probably no need to replace it with larger one.

You can avoid conduit after the breaker panel at shed by using UF-b wire or just installing breaker panel inside the shed then run NM-b.
UF-b wire is rated for direct burial, but need to be buried at 24" depth.

You do need a grounding rod at the shed because it is sub-panel in a detached structure.
Old 03-27-16, 07:20 PM
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20 amps is plenty for the shed (lights, 120V receptacles for light duty table saw and light duty router table
If the saw and router are 120v you may be able to use a multiwire circuit* by changing the breaker to 20 amp and not need a subpanel.

*A 120 amp multiwire circuit would provide two 20 amp 120v circuits.
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