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I am planning on running electrical service out to a newly constructed shed this spring and I wanted to post my plan on this forum to get feedback prior to beginning the work. I will just be using normal DIY hand tools, nothing heavy duty, i.e. welding equipment. The plan: Install a double pole 20 amp breaker at my main panel. The shed is about 50’ from the main panel. I am planning running 12/3 UF-B wire from the main panel to the shed, but I don’t like the idea of not having it a conduit even though it is rated for direct burial, plus I would only have to dig down to 18” (maybe 12”?) as opposed to 24” if it were in a conduit. I guess one question I want to pose would be is there any issue with running UF-B inside PVC conduit? It seems like I’ve seen conflicting info on this. I was planning on using 3/4" conduit, is this a good size for 12/3 UF-B? Once I am at the shed I will run to a double pole 20 amp disconnect switch where I will split off one circuit for lights & one for the outlets using 12/2 NM-B. I plan on installing a 20 amp GFCI outlet at the first outlet. I am guessing that some will suggest upsizing to 10 gauge wires because of the distance from the panel and I am considering it. If money isn’t tight this spring I’ll probably do it anyway but just in case I don’t I wanted to know if I would really be losing that much with the 12 gauge wire. Any suggestions / Comments? Thanks in advance!
 

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UAW SKILLED TRADES
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I am planning on running electrical service out to a newly constructed shed this spring and I wanted to post my plan on this forum to get feedback prior to beginning the work. I will just be using normal DIY hand tools, nothing heavy duty, i.e. welding equipment. The plan: Install a double pole 20 amp breaker at my main panel. The shed is about 50’ from the main panel. I am planning running 12/3 UF-B wire from the main panel to the shed, but I don’t like the idea of not having it a conduit even though it is rated for direct burial, plus I would only have to dig down to 18” (maybe 12”?) as opposed to 24” if it were in a conduit. I guess one question I want to pose would be is there any issue with running UF-B inside PVC conduit? It seems like I’ve seen conflicting info on this. I was planning on using 3/4" conduit, is this a good size for 12/3 UF-B? Once I am at the shed I will run to a double pole 20 amp disconnect switch where I will split off one circuit for lights & one for the outlets using 12/2 NM-B. I plan on installing a 20 amp GFCI outlet at the first outlet. I am guessing that some will suggest upsizing to 10 gauge wires because of the distance from the panel and I am considering it. If money isn’t tight this spring I’ll probably do it anyway but just in case I don’t I wanted to know if I would really be losing that much with the 12 gauge wire. Any suggestions / Comments? Thanks in advance!
I don't see anything glaring wrong in your plan and running uf-b in conduit is ok. Did someone tell you ... cannot do that?

Just might add that if your going to use conduit then you might as will use individual wires like thhn/thwn and forget the uf-b.

A 12/3 G will provide two 20 amp branch circuits when split up at the garage so that sounds about perfect for your needs.

3/4" conduit would be a good choice and would allow up to 4 #6awg if you wanted to run larger awg wire in the future.
 

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Discussion Starter #4
Thanks for the reply Stubbie! Nobody told "me" you couldn't run UF-B in conduit but I thought I ran across a forum thread where it was discouraged. I could be wrong... according to the wife I usually am!!

So here's another question then, all I've done is look at supplies online and the "THHN" wire at all the box stores specifically says in the specs that it is not rated for "wet" conditions. It seems like I've seen this issue discussed and I want to say that it has been said that the "THHN" at the box stores was ok in a conduit BUT since I wasn't sure I figured better SAFE than SORRY.

If you had a conduit with water in it what kind of wire would you rather have in the conduit?

Also, what depth for the conduit? Again, I thought I had read somewhere that if your circuit was 20 amp it could be at 12" but I think I would have to have a GFCI breaker for that?
 

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UAW SKILLED TRADES
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Thanks for the reply Stubbie! Nobody told "me" you couldn't run UF-B in conduit but I thought I ran across a forum thread where it was discouraged. I could be wrong... according to the wife I usually am!!

So here's another question then, all I've done is look at supplies online and the "THHN" wire at all the box stores specifically says in the specs that it is not rated for "wet" conditions. It seems like I've seen this issue discussed and I want to say that it has been said that the "THHN" at the box stores was ok in a conduit BUT since I wasn't sure I figured better SAFE than SORRY.

If you had a conduit with water in it what kind of wire would you rather have in the conduit?

Also, what depth for the conduit? Again, I thought I had read somewhere that if your circuit was 20 amp it could be at 12" but I think I would have to have a GFCI breaker for that?
THHN is dual rated also as THWN. Look on the insulation or the box or the spool it comes in and it will show the dual rating. THWN or THWN-2 is wet rated thus the 'W'. If it doesn't have that dual rating and is only THHN then you couldn't use it underground in conduit.

Running cable like UF-B in conduit is discouraged because it can be difficult to pull thru bends and fittings. There really isn't much point just use individual wires.

THWN THWN-2 would be fine underground in conduit and is designed to deal with any water.

If your circuit to the shed is a single circuit (yours is) at 15 or 20 amps only then if you put the 12/3 on a double pole gfci you could trench at 12".
 

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Discussion Starter #6
Good info Sutbbie... So a 20 amp GFCI breaker at the panel will save me some digging. That's good news! One last thing, with the GFCI at the breaker I no longer need the first outlet to be GFCI protected, right? And can use normal 20 amp outlets all around?

The only downside would be if I overloaded a circuit & tripped the breaker I'd have to go all the way to the main panel to re-set it. If I leave the first outlet GFCI protected it would trip there & not at the panel & I'd only have to go a few feet to re-set it, right? Would you leave the first outlet GFCI protected or pull it to save a few bucks?
 

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Mad Scientist
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If you have a GFCI as the first receptacle, in addition to the GFCI breaker at the panel, it'll be kind of a toss-up which one trips first in the event of a ground fault.
 

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Discussion Starter #8
McSteve - If I understand you right, even w/ the GFCI at the first outlet I might still have to go to the panel to re-set, so having the first outlet GFCI protected is pretty pointless, right?
 

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The way I would do this is run a 3/4 pvc from the panel to a metal 4 square box mounted at say 72" with a double pole double throw light switch and a cover labled disconnect. The reason for mounting so high is that it won't be mistaken for a switch for the lights. This way if you ever decide to put a panel in, you can cut the pvc at any height and mount the panel and have plenty of wire

I
In my opinion 18" is too shallow. Anyone digging with a shovel will hit it. Usually we use a ditch witch and go as deep as it goes
 

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Run two circuits even if you only use one. Also bury a separate ¾” conduit. If you ever want to run cat5, phone line or alarm, etc no digging.

Writer’s information is for discussion purpose only and should be confirmed by an independent source.
 
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