Power to detached storage bldg.

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Old 07-18-13, 10:49 AM
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Power to detached storage bldg.

I have a 24' x 24' pole bldg. in the back yard, and have buried 3/4" PVC conduit between that and the attached garage - about 100'. There is a 30A 240V circuit in the garage sub panel for an outlet rarely used. In the pole bldg. I want a 20A circuit for 3-4 outlets, plus some lights.

It has been suggested I change the 30A double breaker to a 20A double, change to a 20A 240V outlet (which is fine w/ me) in the garage, and connect to that with 12-3 w/ ground to pull to the shed. This would(?) result in 2 disconnect switches in the shed without a sub panel, and no ground rod required. Does that sound right?

I would gfci outlets after each disconnect switch to protect each circuit.

I read on here somewhere that pulling individual wire is easier and cheaper.

The pole bldg. is primarily for storage so I can clear my garage/shop.
 
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Old 07-18-13, 02:04 PM
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Welcome to the forums! Yes, pulling individual THWN wire is so much easier than trying to pull cable.
 
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Old 07-18-13, 02:16 PM
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That's good to know - it may be less expensive, too. But how 'bout the rest of this idea?
 
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Old 07-18-13, 03:01 PM
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Right now you do not sound like you have a neutral at the shed.

A 30 amp subpanel is not much more work and gives added versatility.
 
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Old 07-18-13, 09:36 PM
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Some pictures of the panel in the garage, with the cover removed, would help.

You can run what is called a multi-wire branch circuit (MWBC) between the garage and the shed and not need a grounding electrode (ground rod). You would need space for a two-pole, 20 ampere circuit breaker in the garage sub-panel. Yo would need a SINGLE disconnect in the shed. This could be a DPST 20-ampere rated switch or an unfused air conditioner disconnect.
 
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Old 07-20-13, 12:12 PM
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I can't do a picture right now, but the current 30A double breaker is 240V - one on each phase. I'll replace that w/ a 20A and tie into the only outlet with 12 ga. THHN stranded (it's what my electrician friend has handy) to pull to the remote bldg. As Furd describes, this should create a MWBC.

This friend also suggested a SPST switch for the outlet circuit and the light switch would satisfy requirement for a disconnect.

As I understand it, Red (hot), Black (hot), White (shared neutral), and Green (ground). Does that sound about right?

I've just been reading elsewhere that current THHN wire is double rated for THWN-2 for economic reasons.
 
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Old 07-20-13, 12:15 PM
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You cannot use a SPST switch as a disconnect on a MWBC. You need a double pole switch to interrupt both hots.
 
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Old 07-20-13, 03:59 PM
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As I understand it, Red (hot), Black (hot), White (shared neutral), and Green (ground). Does that sound about right?
Yes.

I've just been reading elsewhere that current THHN wire is double rated for THWN-2 for economic reasons.
You need to pull only THWN wires in buried conduit. Almost all THHN wire is also rated as THWN, but check to be sure.

In order to avoid excessive voltage drop over a 100' run, you should use #8 AWG wires for the two hots and the neutral. The ground can be #12.
 
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Old 07-20-13, 06:51 PM
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In order to avoid excessive voltage drop over a 100' run, you should use #8 AWG wires for the two hots and the neutral. The ground can be #12.
IF you have a fairly well balanced load across the MWBC #12 copper conductors at one hundred feet and a 20 ampere load will result in about a 3.2% voltage drop. That should be sufficient for a few lights and portable power tools. If you need a bit more (less voltage drop) then go to #10 conductors.

In ALL cases, if you upsize the current-carrying conductors to allow for voltage drop you MUST also upsize the equipment grounding conductor a similar amount.
 
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