Questions about buried power to a new shed (Pics).

Below are some images with a schematic.

I need to come out of the house about 5' off the ground, drop down into the ground and then cut across the yard at least 35 feet. I've been reading posts on this board for a while and I have some ideas of what I need to do. I just have a few questions.

1.) From the schematic, what is the best path ? location B to D would be the easiest, but C to D would require less digging. (I would like to reroute a water valve to location C, so this may not be the ideal location for both power and water access.

2.) As I understand it, the wire must be buried 18" deep if inside conduit and 24" if not. (It's also a good idea to place some "Caution buried electrical wire" tape above the wire before covering.

3.) I'm thinking 10-3 and a 30 amp 220V breaker will be enough to run small power tools and lights. Is this correct ?

4.) Will I need a "ground" rod at the shed and what kind of panel box should I get for the shed ?

5.) What size PVC conduit would be enough for 10-3 exterior wire ? (I'll assume the sections must be cemented together.)

Thanks in advance.

If you can get the wire from the inside breaker panel to B on the inside of the house that may be your best bet. Then bury it from B to D.

10-3 with ground would be enough power for a 2hp air compressor and anything smaller like your hand tools.

I guess in the new world of electrical a ground rod at the shed is used but in days past it was never thought of and worked just fine.

Is it code that you have to use conduit under ground? We can direct bury underground wire here.

Gary

Thanks Gary,

I believe if I bury 24" or deeper conduit is not required. 18" to 24" requires conduit. 18" is minimum. Since I'll be digging by hand, that last 6" of depth may or may not be a big deal. I do like the idea of extra protection too.

Also, I don't think an extra ground rod will hurt anything.

In conduit to allow future service and tape buried a few inches above are excellent ideas.
For all the length of the run and to limit light dimming or brightening when tools are started. #6 wire and a 60 amp service are recommended. Plus in the future you will wish there was more than 30amp out there.
A 10ft ground rod and #6 bare copper is required out at the shed. Open the bond between the neutral and ground bars.
Four wires to shed. Two coloured, a white and a bare or insulated ground.

Red, EXCELLENT Question. Myself (retired electrical distribution design engineer) and other professionals as well as lay people have covered this great question MANY times here before so let me just try to summarize some information for you.

1) YES 3 conductors will suffice IFFFFF you only need 120 volt service at the shop. That would be a HOT, a Neutral, an Equipment Ground fed from a single pole 120 volt breaker at the main panel. Breaker sized to the wires ampacity i.e. 20 amp for 12 gauge or 30 amp for 10 gauge

2) NO 3 will NOT suffice if you want 240 at the shop. If you want 240 plus 120 then YOU NEED 4 CONDUCTORS. Two Hots (L1 & L2), Neutral, Equipment Ground. That will require a two pole 240 volt breaker at the main panel. Breaker sized to wires ampacity again.

3) YES all building electrical services require a Grounding Electrode. That may be one or more made electrodes such as driven into the earth copper ground rods and/or conductive water pipes SUBJECT TO LOCAL AUTHORITY REQUIREMENTS

4) SUBJECT TO LOCAL AUTHORITY you can use cable rated for direct earth burial (like Underground Feeder UF or Underground Service Entrance USE) or you can use cable or single conductors like THWN rated in buried PVC conduit provided its NOT under a driveway.

5) Sub panel at shop. YOU MUSTTTTTTTT KEEP NEUTRAL AND GROUND BUSSES SEPERATE AND ISOLATED !!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Unlike at a main panel where the two are bonded together THIS IS IMPORTANT AND FOR SAFETY AND IS A STRICT CODE REQUIREMENT assuming your local authority (if any exists) has adopted the latest NEC

6) Wire size: Sure 10 gauge is 30 amp rated but if the distance is great and if youre gonna have continuous loads of more then 24 amps YOU MAY WANT TO UPGRADE TO 8 GAUGE TO REDUCE VOLTAGE DROP

I gotta run but will check back later today if you have questions I did this in a hurry and its NOT complete but the basics for your safety and code compliance if that matters?? Maybe the other professional electricians and engineers and other fine knowledgeable gentlemen etc can add to this for what I missed being in such a hurry

John T Long retired EE and rusty on the latest code but believe this is all correct

I recently ran 100 amp service to my barn going underground. I put it in conduit in case it needed to be pulled out. Over the past 40 years there has been 3 different sets of lines run to the barn and all three died from lightening strikes. I bought the place 5 years ago from a family member so I know the history. This was felt to be caused by the panel in the barn not being grounded properly. It was grounded to a plastic water line!! I hired an electrician as a consultant and he told me that ground rods were required to meet code here. I would recommend going one size larger on the wire than you think you need. You don't want to be redoing this in 10 years when your electrical needs go up.

just ran new underground service to house. had to be in conduit buried 24" and it was a direct burial wire from the power company. from the power center ran 2/0 power with 1/0 neutral to barn breaker box and put ground rod at barn. about 100' from house, on 100 amp breaker.

It could be buriud at 18" . Burial depth goes by what is above the trench etc. To do that much labor and only run 10 awg? Why not put 60 amp conductors? Although for what you quoted 10 guage will work. 3/4 pvc minimun. But same thing for that much labor I would lay 1 1/2". { for future use which is a code requirement also].

JT,

The 10-3 will have 3 coated (black,red,white) plus a bare ground.

I won't need 240v, but I would like two separate 110V circuits -- 1 for lights and two outlets, and one for three other outlets. I don't have anything requiring a higher amperage than a circular saw.

It is my understanding that the two 110v circuits can share the neutral. Am I wrong on this detail ?

I will consider a heavier wire.

Thanks,

"#6 bare copper" I assume to connect the ground rod to the sub-panel !?!

John T & Buickanddeere always have good electrical advice so no need to repeat their info. But do study out what they say and why.

The 4 wires, and the exact way to ground everything is kinda important these days. It seems strange at first, but if you wire up the ground (bare or green) wire wrong, everything will work and appaer fine. Until someday you _need_ that ground wire. It's purpose it to provifde safety, in a perfect world that wire will never ever be used, it only comes into play to prevent fires, and electrocutions.

But, it needs to be wired right, to code, to work properly. And you don't find out if it's right or not just by turning the breaker on. So pay attention to the isolated ground straps, and such, that those guys mention. The details are important for 10 years from now when your kid or neighbor plugs something in and some wire breaks or shorts and _then_ you'll find out if you did it right or not.... The ground wire stays spererate all the time except at your main (probably house in your case) breaker where it is on the same ground as the nuetral wire. But that is the _only_time they should be bonded together, or you set up odd loops that can put floating current on all your grounded stuff.

You mention something about coming 5 feet out, and then down. That might catch the attention of the inspector, what are you coming 5 feet out on, how you handling that, what's the story? Horizontal exposed conduit laying on concrete doesn't sound right....

And, if you are bothering to dig this trench, and bothering to do the work and expense of wiring up the building, why not upgrade to at least a 50 amp service out there? The only extra expense is going to be the wire, at only 50 feet or less that is not much cost, and a bigger fuse in your box, same or a couple bucks extra. Five years from now when the lights dim every time you start your grinder and you can't buy the welder you wanted because it draws too much juice, you'll be kicking yourself every weekend you are there for skimping on the cost of a couple cases of beer. Think on that a little.

--->Paul

I've had great luck with #2 URD cable which is a direct burial aluminum cable. USE DEOX ON ALL TERMINATIONS and stip the wire properly.
NEC 2008 300.5;
24" minimum cover direct burial cable
6" minimum cover rigid conduit
Use a 60 amp breaker at the house and a 6 or 8 circuit subpanel in your building. Keep your lights on 1 or 2 seperate circuits so that when you trip a recp circuit you will still have lights.
Grounding per code
good luck
Ron

The 5 feet I was referring to is the distance on the outside of the house between the sod and the middle of the joists for the second level... which works out to be about 1.5 feet above the top edge of the lower windows on the 2nd picture. The conduit would come out of the house at this point and then go straight into the ground directly against the siding.

I could try to get down into the wall cavity. and come out right above the base plate. That will take a little more effort to pull off but will look cleaner without that extra exposed conduit.

I appreciate the heads up on the grounding. I think I'm understanding how to do that correctly now.

Okay, then you DO have 4 wires. From your post I took you to only have 3. Yours is 3 PLUS Ground. Red n Black Hots,,,,,,,White Neutral,,,,,,Bare Ground

THEREFORE thats enough for 120 and 240 OR you can just use two legs of 120 volt and YES share the Neutral........

YES the common white Neutral serves as the return for BOTH 120 volt supplies and as a matter of fact if both loads were balanced then the Neutral current would be ZERO as the two phases are 180 opposite from each other.

If youre just gonna run a couple 20 amp circuits out there and the total distance is under 75 or so feet, then I can backpedal on my post above and say 10 Gauge will work. I was thinking you were gonna feed 30 amp circuits when I suggested 8 gauge.

You can buy that gray colored 10/3 PLUS Ground (4 wires total) UF direct burial rated cable thats not too costly

John T

John,I hope I can say this politely,as far as outbuildings wiring from a central point.You go by the Electric Co.rules,NOT NECs book.Our Elec.Co.and some others will only allow 1(one)ground rod PERIOD.We have 3 Elec.Co.close and they(each)WILL NOT PERMIT WHAT any of the other 2 will(diff.wire specs-diff box specs-ground ruling.)So you go by local rules,not by your code book.

Got it! External drop onto the ground is fine no prob. My brain took a different track.

--->Paul

Correct #6 bare copper from shed panel ground lug to a 10ft ground rod. Better ground at she"d and beefs up the house ground system too.

Direct burial an be done in any electrical jurisdiction but is a troublesome and short sighted activity. PVC conduit is cheap and allows pulling cables without digging if there is a future fault. Chances of faults are also reduced thanks to the protection from the conduit. Just because something "works" does not make it "right".

Was just thinking of your shed and the updates to mine that is the next project here. Mrs B&D gets all hostile when grease , mud and manure is tracked onto the garage door knob and floor. Mood declines farther if any dirt is found on floor, bathroom or laundry room fixtures and sinks. At minimum there will be a laundry sink and under counter heater . There maybe enough grade between your shed and house for a drain. May as now at least run a water supply and drain line between the buildings. Won't cost very much and can be finished in the future. I'm thinking for here maybe even a shower, beer fridge, tv , microwave etc . If my daughter has a bunch of teeny boppers over. The shed will make a good place to hide.

How does that work when you come down the side of the house that is set below frost, so it doesn't move, and the conduit is in the ground horizonally and will flex up with frost.

Seems to me the conduit will snap. And I have seen it happen.

When direct burying the wire you run it straight down below the end of the pipe, 6 or more inches, so it can flex up and down in the pipe before bending it to run horizonally with the trench.

Just an observation of what can happen when running conduit down a house then out.

I have also seen where they bend a 90 on the conduit bottom under ground and the frost shears off the wire where it comes out of the conduit 90.

In warm climates this is a non issue.

Gary

Yep thats why I tll people do what THE LOCAL AUTHORITY SAYS NOTTTTTTTTTTTT ANY OF US HERE

John T

Good point.

They make an Expansion coupling which is sealed with an 0-ring and it appears to be of reasonable quality. This might be appropriate in this situation. I do get some ground movement in this heavy soil.


Link to Menards Expansion Coupling...

Just repeating what my father-in-law told me when I built a garage 30 some years ago. Code & policy might have changed since then. He was a licensed master elec, so I took his word for it. Run conduit down to proper depth, put a 90 deg sweep el, then extend 10 feet. This will flex a bit to allow for frost movement. Since it was only a 15 foot run, did conduit all the way.
Willie

Well you really have me worried. I know I have FOUR large wires from house to shop/ If you look at a post I put up tonight about a generator you will see I leave OUTSIDE the house to the shop but WAS required to have a gound rod outside now I AM not certain the shiny copper and the green do not go to the same bar in the shop box. Going to have to do some checking.

You can use one of those but in a 35 ft run it is not necessary.