Ask Me Help Desk - Detached Building Wiring

I think I have most of the wiring requirements down for this, but have a couple of questions. I have a detached shed approximately 60ft from my house. I'd like to run electricity from a subpanel in my garage to the shed.

I have planned on burying 1.5" conduit to run 4 #4 wires (2 hot, 1 neutral, and 1 ground) from the house to the shed. I've also planned on sinking 2 grounding rods at the shed to connect to the subpanel. I will be using a 70A double-pole breaker in the garage to push a couple of 20A circuits in the shed for lights and small tools.

1. The run from the shed to the garage subpanel will be about 60ft buried and about 20ft through the house walls. Can I run the 4 wires all the way through the walls to the subpanel? Or do I need to run something else through the walls and then "splice" them outside the house just before they get buried?

2. Does the subpanel in the shed need to have it's own main breaker? Our house is wired with a main disconnect at the meter itself...

1) NO, you cannot run individual conductors unless in conduit or a raceway. You can run cable and splice to the conductors in conduit. The splice must be in an appropriately sized box.

2) Yes, the detached structure must have a form of disconnect. A main breaker is the easiest way to do this.

rzapalac

I hope this info helps you out.

1.#4 wire is good for the 70 amps you want to use. The ground wire can be downsized on residential if you want to save on some money. #4 is okay if you want to stay with it.

2. You only need one grounding rod for the sub panel. The first means of grounding is your #4 and the second means of grounding will only need to be one ground rod at least 6-8 ft down.

3. If you run the wire through the walls or in the ceiling it must (1) be sleeved with pvc or use 4/3 Romex. This will give you your 2 hots, 1 neutral and one ground all in one. Mount a junction box on the outside of the house and run your buried conduit from the junction box to your new sub panel.

4. I don't think the sub panel needs a main because the disconnecting means will be your 2 pole 70 amp breaker.

I hope this helps you out. FYI, you might want to have your plugs GFI protected. Use 20 amp GFCI's for #12 wire.

I hope this helps you out.

Quote:

Originally Posted by patcolamp

2. You only need one grounding rod for the sub panel. The first means of grounding is your #4 and the second means of grounding will only need to be one ground rod at least 6-8 ft down.

Well, first of all the ground rod has nothing to do with the equipment ground run with the feeder. They serve two very different purposes. They are NOT a "first" and "second" ground. You do need <at least one> grounding electrode (typically a ground rod) at a detached structure with a sub-panel. The equipment ground run with a 70-100 amp feeder needs only to be a #8cu.
See NEC 250 III and T250.66

Quote:

Originally Posted by patcolamp

4. I dont think the sub panel needs a main because the disconnecting means will be your 2 pole 70 amp breaker.

The 70 amp breaker is protecting the conductors. You absolutely DO need a means of disconnect located at the detached structure.
NEC 225.31

Quote:

Originally Posted by patcolamp

I hope this helps you out. FYI, you might want to go ahead and have your plugs GFI protected. Use 20 amp GFCI's for #12 wire.

ALL 15 and 20A receptacles in unfinished areas of a residential out building require GFI protection.
210.8(A)(2)

20A receptacles are NOT required unless it is a single receptacles on a dedicated circuit.
210.21(B)(3)

Are you at all familiar with the NEC?