Power to a Detached Garden Shed

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Old 11-17-18, 04:14 PM
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Power to a Detached Garden Shed

Hello All,

I need some help and assistance.

I built a garden shed this summer and plan to run power to it next spring/summer.
I will have little power requirement, probably 2 light circuits and one outlet strip. I cant imagine ever pulling more than 30A at any point. No need for 240V...

I will be working on the garage in the next few weeks, and while the walls are open I'd like to pull line from the main panel to a JB where I will ultimately leave the house in conduit to the shed. I'll run 100ft through the house to the JB, and then another 100 ft in conduit to the shed next year. Will I need to worry about voltage drop at this length?

This is what I'm thinking:

30A dual pole breaker in the main.
10/3 romex through the house to the JB in the garage
Splice to 10/3 UF-B in 3/4" conduit 18" down to a 60 A sub-panel in the shed.


Does this make sense?
Is it cost effective?

An alternative could be:
20A single pole in the main
10/2 romex through the house to the JB
Splice to 10/2 UF-B and direct bury at 12" to a sub-panel in the shed.

Would both options require sinking a ground rod at the shed?
Neutral and ground would only be tied at the main.

Thoughts?

Thanks,

Bryan
 
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  #2  
Old 11-17-18, 04:52 PM
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Voltage drop is an issue at 200ft. You'll be limited to pulling about 12A at 120V using 10/2 or about 24A at 240V using 10]3.
 
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Old 11-17-18, 05:42 PM
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I dont see myself ever needing the full amperage. Its really just for lights and a convenience outlet. That said, I probably should do it once and do it right...

For the increased cost I think I'll run 8/3 and be done with it.

Seems the w1re cost between 10/2 and 8/3 is near $1.00/foot. So $200 extra and I'll probably be happier in the long run.

Am I missing something?
 
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Old 11-17-18, 06:19 PM
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If it were me, I'd probably just run four 12ga wires (THWN) in 3/4" conduit. That'll give you 2 20A circuits without the need for a subpanel in the shed. You'll still need a disconnect, but a double-pole switch or AC disconnect would satisfy.

That'll save you a couple hundred dollars, and I can't imagine using more than that.

Of course your plan using 10ga or 8ga wire into a subpanel is fine too. Though if you're using conduit, pull THHN/THWN wire through, don't try to pull UF-B through it.
 
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Old 11-17-18, 06:44 PM
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If it were me, I'd probably just run four 12ga wires (THWN) in 3/4" conduit. That'll give you 2 20A circuits without the need for a subpanel in the shed. You'll still need a disconnect, but a double-pole switch or AC disconnect would satisfy.
How would you handle the ground in this configuration?
 
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Old 11-17-18, 07:31 PM
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IMHO #12 at 200ft is about worthless.
 
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Old 11-17-18, 08:19 PM
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A single circuit to the shed does not require a ground rod. A multiwire branch circuit is considered a single circuit.
 
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Old 11-18-18, 07:01 AM
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How would you handle the ground in this configuration?
The 4-wire in conduit will be two blacks, one white, one green. (H/H/N/G) That gives you two circuits at 20A each.

And I'll revise my statement based on pattenp's comment
IMHO #12 at 200ft is about worthless.
I'll agree. At 200' I would do 10ga if you're just running some lightweight loads. With 10ga wire, it gives you basically 2 circuits at a reasonable 15A load each with 5% voltage drop. Lights, a few power tools, small refrig. I think you're good.
 
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Old 12-20-18, 02:18 PM
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I started the interior run with 8/4. Figured I'll be happy to have soe capacity in the shed down the road.

Anyhow, I need to land the cable at the Panel. I have little room in my main panel, can squeeze it in, but wiring is getting tight and the #8 isnt easy to work in tight spaces.

I have plenty of room in a 100A sub-panel.

Is there any reason I can feed the shed from the sub-panel?

Thanks,

Bryan
 
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Old 12-20-18, 02:21 PM
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As long as your subpanel isn't overloaded electrically from very large loads, it would be no problem to power the shed from it.
 
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Old 12-20-18, 02:28 PM
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yeah, the sub has space and capacity.
I'll never pull the 40A at the shed anyway.

That brings up another question.

Someone calculated above that at 200+ feet I'll only be able to pull 30ish amps.

If this is true, should I feed the 8/4 with a 30A breaker, as if its fed with a 40A and I short it may be slow to trip given the drop associated with the long run....
 
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Old 12-21-18, 08:50 AM
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It is not strictly required by code to downsize the breaker for voltage drop, but I think it's a good idea to do so. Code considers it a design choice rather than a safety issue.
 
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Old 04-03-19, 02:31 AM
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Spring has sprung, and its time to finish this project. I have my run of 8/4 from the sub to the edge of the garage where I will transition to conduit buried at 18".

I plan to run 3 #8 THWN stranded cables and a green ground. What gauge green ground do I need to run?

At the shed panel I will keep neutral and grounds isolated and also pound in a ground rod tied to the ground bus.

Am I missing anything here?

Thanks.

BK
 
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Old 04-03-19, 02:54 AM
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#10 for ground should be okay for #8 on a 40 amp breaker.
 
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Old 04-03-19, 06:49 AM
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Note: An "8-4" cable (or any other cable) must have a bare or green covered wire for use as the equipment grounding conductor. Normally an 8-3 with ground or 10-3 with ground or whatever size desired is used for this project. An "8-4 with ground Romex" technically includes a fifth conductor for ground and the usability of the fourth conductor may be very limited. Such (non-green covered) 4'th conductor may not carry power to the detached shed as part of a separate branch circuit for a total of 5 conductors going out there. Three conductors (plus ground) can be configured as a single branch circuit (a 120/240 volt multiwire branch circuit) which is proper to feed a separate building and is the typical method of doing so.
 
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Old 09-23-19, 03:23 PM
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I didn't know whether to hijack this thread or start a new one since this project is similar to mine. So I'll try the hijack method and see how it goes.

I want to run 2, 20A circuits out to a pool pump and shed. It's a 100' run from the panel. I do not intend to install a subpanel. The pump needs a 20A circuit according to my pool installer. The other 20A circuit will be for a light load in the pool shed (LED lighting, maybe a ceiling fan and small fridge). I'd put a double pole switch in a box on a pedestal (because the pool will be done before the shed), and feed the pool pump and shed from there.

I was thinking of doing exactly what Zorfdt recommended. 4 12ga wires - 2 blacks, 1 white one green:

"If it were me, I'd probably just run four 12ga wires (THWN) in 3/4" conduit. That'll give you 2 20A circuits without the need for a subpanel in the shed. You'll still need a disconnect, but a double-pole switch or AC disconnect would satisfy"

Sound like a good plan?
 
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Old 09-26-19, 12:28 PM
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I would go with 10 gauge wire (two hot, one white, one green) for some future expansion capability.

You can start with a 20 amp double breaker back at the house main panel and no subpanel at the shed.

Ultimately you could have a15 amp and a 20 amp regular circuit on one side and the pool pump plus a 15 amp regular circuit on the other side when you upgrade to a 30 amp breaker and add the subpanel (and keep the 10 gauge wiring).
 
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Old 09-30-19, 06:29 PM
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Thanks! Sounds like a plan.
 
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Old 10-04-19, 01:17 PM
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One other quick question...

I can run something like Southwire's "Ultratite" flexible conduit from end-to-end, right? Underground, in the basement and right to the panel?
 
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