[cowsgonemadd3]

I have purchased a 12x20 shed. Now I need to get power to it. It will be a work shop so I am going to use 8/3 UF cable buried in conduit until I get to the house.



I have plans to add a junction box under the house and then run from there with standard wire to the breaker box where it will go to a double pole 50 amp breaker. We are running 220v.



I know I need a spool of 50ft 8 gauge UF wire for the trench to the building. When I leave my junction box to head to the main home box, what wire do I need? Do I need to get 6 gauge wire from the junction to the breaker box under the home?


Oh and just to vent, 8/3 UF wire is expensive.


Thanks for the help

 

[roughneck]

It should be a sub panel in the shed. You’d head right to the existing breaker box in the house, and mount a new sub panel in the shed.
Avoid junctions or splices if at all possible.
What service do you have in your house?

 

[NCmountainCabin]

your shed can use a 'main lug' panel instead of a 'main breaker' panel as the sub-panel from the house's main panel, which saves you a double-pole breaker to wire to in the shed... it just has main 'lugs' to attach your two Hot Wires to, a Neutral lug/bar, and a Ground lug/bar(some do not include the ground bar, so check and see and get one to add to this since a sub-panel needs to have a ground bar and Neutral bar separated). Look up a 50, 60, or 70amp 'main lug' panel at the big box boy stores and see. Inexpensive,too, if that's all the 'power' you need in the shed, anyway. It could handle two to four circuits, either 30, 20, or 15amp, though a shed, with power tools, is probably well suited for 20amp circuits, and you can buy the 'tandem' type that would take two spaces but give you FOUR different circuits - one for lights/fans/light usage, and three for 20amp outlets for power tools, since that would work for almost any 'normal' power tool.

what this also means is that, while it is slightly easier wiring, you have the main breaker in the home's panel, not out in the shed, which is o.k. for some, and others would rather have a sub-panel with it's own main breaker.

I would use 8/3UF and just bury it, you don't need any additional conduit since it's already in it's own conduit. When you come up into the house, within the wall I suppose, you go into the Home's breaker panel, and to a 50amp double-pole breaker, which will serve as your 'sub-panel's main breaker.

 

[cowsgonemadd3]

200? Amp to the house. Its a really big double pole breaker.



This is what I bought for my shed. https://www.homedepot.com/p/Square-...ERCH=REC-_-pipsem-_-100190554-_-100149777-_-N


I bought (6) 15 amp breakers to go in the box and around (13) 15 amp outlets to go in the shed. I looked into 20amp outlets and breakers but that required heavier wires in the wall(more cost) and most tools I looked at use no more than 15amps max. Is it worth an extra $85-100 bucks to go with 20 amps? I already bought all the wiring, breakers and outlets.



I do not want to run UF cable up under the house clear to the houses main box. The stuff is brutal in cost. I wanted to buy a roll of this for underground:
https://www.homedepot.com/p/Southwire-50-ft-8-3-Gray-Stranded-CU-UF-B-W-G-Wire-14783522/300916642


And then run something from a junction under the house to the houses main box if possible.


By the foot pricing is really high compared to a spool:
https://www.lowes.com/pd/8-3-UF-Wire-By-the-Foot/3129381


I think I need like 65ft or so. Unless anyone knows of another option for my issue?

 

[NCmountainCabin]

that's a 100amp 'main lug' sub-panel, which will require the wire size for a 100amp circuit back to the home's panel, which is very large, and your home's panel will have to have a 100amp double-pole breaker installed to provide for this power to the shed.
While you could get away with a much smaller 'sub-panel' breaker in the home's panel to the sub-panel in the shed, such as a 30amp double-pole breaker, which would only require 10/3 wire cable to the shed's sub-panel, most electricians would say that code requires you to wire it to the correct size of the panel, for future usage, especially if someone later doesn't realize that the wire going back to the home's panel is not sized for the 100amp panel in the shed.
If you changed out this 100amp panel for a much smaller 50amp or similar size, with two or four circuit spaces, you would have a lot less wire size to be concerned with.

 

[NCmountainCabin]

also, just to clear up your wording, you say 'under the house', but we have no idea what that means...

 

[jreagan]

that's a 100amp 'main lug' sub-panel, which will require the wire size for a 100amp circuit back to the home's panel, which is very large, and your home's panel will have to have a 100amp double-pole breaker installed to provide for this power to the shed.

Uh, no. While the panel is rated for 100A, you can feed it with 20A if you want. The breaker back in the house protects the wire going to the shed.

 

[NCmountainCabin]

that's what I stated, as an option, but the problem comes in when a 'new' owner down the road doesn't REALIZE that only 12/3 wiring is run from the house to the sub-panel, and they decide to add more circuits, change the main breaker out to a 50 or 100amp, etc. The wiring to the shed then is not able to handle that, which is the very reason for the original wiring to be up to the size of the sub-panel, regardless of whether the main breaker is of that same size.

 

[cowsgonemadd3]

Yeah, I got that one because it has 6 spaces. I want to wire up multiple things on there on 15 amp circuit. Lights get there own 15 amp and so on. I can add a sticker to the box saying what was fed to it. Label maker for the win.


Under the house means, I run 8/3 UF to the house in a trench, once "under" the house and out of my max 50ft of UF wire, I add a junction box and some other wire thats not expensive UF to the houses main power box with a double pole 50 amp breaker.

 

[Chris130]

Yeah, definitely reconsider the plan to put that UF in conduit - you're going the have one heckuva time making that happen (if you can at all).

Check your local codes for any gotchas, but you should be able to just lay the UF bare in a deeper trench (~24" versus a shallower required depth if in conduit).

 

[7635tools]

If your planning on putting in conduit in the trench, then why not conduit all the way to the panel and pull individual conductors. PVC is cheap. I’m not 100% sure but I think 8/3 UF cable is only good for 40a. If you want 50a, then you would need a 6/3 cable. If you put it in conduit all the way and pull individual copper conductors, then #8’s are fine on a 50.


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[HotRodx10]

...the problem comes in when a 'new' owner down the road doesn't REALIZE that only 12/3 wiring is run from the house to the sub-panel, and they decide to add more circuits, change the main breaker out to a 50 or 100amp, etc.

I don't think it's necessary or required to guard against what the next owner might do. Replacing a breaker with a larger capacity one, without first verifying the wire can carry the larger current, is both stupid and illegal. In my experience (which granted, isn't extensive), service panels are rarely, if ever, wired for their rated capacity.

 

[cowsgonemadd3]

#8 seems to work for 50 amps from all I read online but what would conduit have to do with more amps of the wire?


We were going to go with conduit as this will be shallow buried. Below this could be other lines and we know they will be at 24" or deeper. I was aiming for 8 to 10 inches in 1 1/4 conduit. Or if I can skip the conduit and direct bury like the package says that would be nice.

 

[7635tools]

that's what I stated, as an option, but the problem comes in when a 'new' owner down the road doesn't REALIZE that only 12/3 wiring is run from the house to the sub-panel, and they decide to add more circuits, change the main breaker out to a 50 or 100amp, etc. The wiring to the shed then is not able to handle that, which is the very reason for the original wiring to be up to the size of the sub-panel, regardless of whether the main breaker is of that same size.

It doesn’t matter if they have a 200a breaker in the sub panel, the breaker in the main panel feeding the sub is what protects the wires going out there. If the new home owners are that stupid then they shouldn’t be working on electricity.


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[rjniles]

Copper #8 in cable is only rated for 40 amps, to get a 50 amp rating you need #8 copper in conduit. The conduit would have to be run continuous from the house panel to the shed sub.

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[Sparkyb60]

Detached buildings (garage , etc ) require a main disconnect. A main lug panel is not acceptable. A small 100 amp Homeline panel would be cheaper than a qo panel. You need to purchase a separate ground bar and
ground rod . (To keep the neutral and grounds separate ) 8-3 uf is good for 40 amps. Under the house may require uf cable or conduit.

 

[Jim Port]

that's a 100amp 'main lug' sub-panel, which will require the wire size for a 100amp circuit back to the home's panel, which is very large, and your home's panel will have to have a 100amp double-pole breaker installed to provide for this power to the shed.
.

Simply installing a 100 amp panel does not mean it needs to be fed with 100 amp components. One hundred amp is the maximum it can be fed with.

most electricians would say that code requires you to wire it to the correct size of the panel, for future usage, especially if someone later doesn't realize that the wire going back to the home's panel is not sized for the 100amp panel in the shed.

Nonsense. It only has to meet the design criteria at the time of install.

your shed can use a 'main lug' panel instead of a 'main breaker' panel as the sub-panel from the house's main panel, which saves you a double-pole breaker to wire to in the shed... it just has main 'lugs' to attach your two Hot Wires to, a Neutral lug/bar, and a Ground lug/bar(some do not include the ground bar, so check and see and get one to add to this since a sub-panel needs to have a ground bar and Neutral bar separated). Look up a 50, 60, or 70amp 'main lug' panel at the big box boy stores and see. Inexpensive,too, if that's all the 'power' you need in the shed, anyway. It could handle two to four circuits, either 30, 20, or 15amp, though a shed, with power tools, is probably well suited for 20amp circuits,

The panel needs a means of disconnect. Main lug panels do not provide the required means of disconnect.

I would use 8/3UF and just bury it, you don't need any additional conduit since it's already in it's own conduit.

Not true. Protection would be required from 18 inches below grade to some distance above grade..

NC, you really need to review your answers before posting. Much that you have posted is not correct.

 

[rjniles]

A main lug panel can be used in a detached building. The main disconnect can be 6 or less handle breaker throws or a back wired breaker used as a disconnect.

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[seharper]

I have purchased a 12x20 shed. Now I need to get power to it. It will be a work shop so I am going to use 8/3 UF cable buried in conduit until I get to the house.

OK. Have you ever done conduit running before? Why are you selecting cable for running inside conduit? I can't speak for your case, but 90% of the time it's a novice, who knows nothing about conduit, knows only cable and does not know/trust THWN wire. There's nothing wrong with that; it's just a knowledge gap; but it'll lead you to a blunder.

Just to fast forward, other common novice errors are:

- Scrimping on the electrical panel, saving pretty much the cost of *a pizza* and then running out of breaker spaces soon after, and having do an expensive re-do.
- going with copper when they should be using aluminum (now you have the worst case; wasted money on wire AND a future panel-space crisis).
- Insisting on using cable and then failing to buy the *ginormous* conduit cable requires. 8/3 UF requires 1-1/2" conduit. 6/3 UF requires 2" conduit.
- getting so frustrated with pulling the balky uncooperative cable through the too-small conduit that they assemble the conduit pipes around the cable - nope, that's illegal.
- Burying too shallow (you need 18" *of cover* unless you're using very pricey Rigid conduit).

To fast forward to the right answer, since you state later you want 8" burial depth... SO. 3/4" Rigid conduit at $2/foot, or 1" Rigid conduit at $3/ft. That's because of your shallow burial depth; it's your only choice. The Rigid connects your new subpanel to a steel junction box inside the house. This will involve actual pipefitting, thus a trip or two to the hardware store to have them cut and thread your pipe. Then, into the pipe goes ONE of the following:

- 3 x 8 AWG copper THWN or XHHW wire ($.33/foot/wire) -- 50A
- 3 x 6 AWG aluminum THWN or XHHW wire ($.20/foot/wire) -- 50A
- 3 x 6 AWG copper THWN or XHHW wire ($.52/ft/wire) -- 70A

Unfortunately colors must be 1x white and 2x non-white. If you bumped to 1" Rigid and use 4 AWG wire (aluminum, say) you would be able to just get one spool of wire and mark the wires with tape.

Notice there is no ground. The Rigid pipe *is* the ground.

------------------------------

Now, the 2nd half of this is getting from the main panel to this junction box. You can use any of these:

- 6/3 w/g copper NM-B cable (regular Romex)
- 4/3 w/g aluminum cable
- PVC conduit - in which case you must run a #10 Cu or larger ground wire from main panel to junction box.
- EMT metal conduit - no ground wire needed if you do this

If you use either type of conduit, then the 3 wires can *run straight through* the junction box and not even stop there. In fact, if it's EMT metal conduit, you can skip the junction box altogether and just use a "pulling point" e.g. a conduit body. You want to put as many pulling points in as you can, at or between bends.

That's how I'd do it, and I do a lot of conduit work, and I'm cheap, and I'm lazy.

"cheap" may not seem compatible with paying $2/foot for conduit, but that's because I'm too cheap to rent a ditcher and too cheap to pay for the damage to the other utilities that I slice through. Rigid only requires 6" cover, so you can trench it with a garden trowel.

 

[seharper]

By the way, the person saying "you don't need a main breaker panel" You need a main-breaker panel. Last time this came up, someone was hell-bent on a $20 panel, I found a $70 main-breaker panel that came with $20 worth of bonus breakers, so only $30 more in the net. That person will never run out of spaces.

You need more than 6 spaces because you can power about 250A of breakers worth of stuff in that panel, and you're only at 90A with your panel full. What a waste. Skip the pizza one day and get a nice panel.

"Wait, how can I power 250A worth of breakers?" Easy. For general loads you use occasionally, you get to factor for the fact that all the loads will never be used at once.

Yeah, definitely reconsider the plan to put that UF in conduit - you're going the have one heckuva time making that happen (if you can at all).

If someone absolutely must, I recommend going 1 size larger than the required conduit. So that'd be 2-1/2" since OP will inevitably have to go up to 6/3 UF to get 50A with UF cable. Rigid 2-1/2" is about $8 a foot, so somebody would really have to love their cable to spend $400 on that.

Check your local codes for any gotchas, but you should be able to just lay the UF bare in a deeper trench (~24" versus a shallower required depth if in conduit).

Yes. 24" of cover is fine for direct burial.
PVC conduit requires 18" **of cover**. I.e. above the top of the conduit.
Rigid and IMC conduit require 6" of cover.

#8 seems to work for 50 amps from all I read online but what would conduit have to do with more amps of the wire?

No. UF-B pulls from the 60C column of Table 310.15(B)(16). That puts #8 Cu UF at 40A.

THWN and XHHW pull from the 90C column, except it's impossible to find 90C terminations, but common breaker and panel lugs allow 75C, so they can pull out of the 75C column.

We were going to go with conduit as this will be shallow buried. Below this could be other lines and we know they will be at 24" or deeper. I was aiming for 8 to 10 inches in 1 1/4 conduit. Or if I can skip the conduit and direct bury like the package says that would be nice.

<18" of cover obliges you into Rigid conduit.

1-1/4" conduit is too small for 8/3 UF cable. I hope we've talked you out of that!

FYI you measure or look up the wide width of the cable (1.065" in this case) and multiply by 138% to give the minimum pipe inside diameter.

If you test fitted it in Home Depot, I bet you used a pipe fitting - that has the outside diameter of the pipe.