What gauge wire to lay underground?
 

Hi, DH and I are building our barn, roof is on, now it's time for elec and water. Can I lay the wire in the same trench as the water line? It will be about 18 to 24 inches deep using a ditch witch. I also need to know what gauge wire to use, I've seen 12 and 10 gauge mentioned but not what the difference will be. I'll only have one outlet and up to six light bulbs or flourescent fixtures.
Any ideas?

It's against code to run the power and water in the same ditch. The ideal way to run power to your barn would be to run #3 in conduit to a small 125 amp sub panel in your barn. It would be more costly up front, but if you did ever need more power for something (like a welder) in your barn you'd have the power available. If you don't want to do that, the 12 will be fine up to 100 feet or so. Longer than that and I'd run the 10.

can we assume it would be against code to run natural gas in same trench as electric as well? i was thinking of doing that when i dug the trench for electric

If you are not required to get involved with an inspection, don't worry about running the water and power in the same trench, it been done a million times, and the only issue is repairs. It's tough to dig one up without damaging the other. Remember all well trenches have water lines and power run in the same ditch. Assuming your ditch is less that 100' or so, I would run one 20 amp circuit from the house. I would run a piece of 12/2 romex and install it in 3/4" pvc conduit. The biggest problem with underground power is that rocks tend to work themselves into the cable and cause problems.

Do not run 12/2 Romex.
Romex is not suitable for underground installation (Article 336, National Electric Code).
For your application the length of the run will determine the size of the wire. Personally I would use #10 AWG Type UF cable (gray jacket) buried in the same trench. If you examine how your well was installed, the water line and Type UF electric cable are installed in the same trench. #10 will be good for about 150' or so. If you have a little extra money consider using 10-3 with ground instead of 10-2 with ground to allow use to install 240 volt circuits at a later date if the need arises. It keeps your options open at a later date. Plan on installing a seperate ground rod at the remote building and bond with #8 AWG bare copper. All plugs not being used for a dedicated purpose (single plug) should be GFCI receptacles.

Silly me, with decades of experience and ability to read!!!! I recommended that he run the Romex in PVC conduit, which contrary to your claims is perfectly legal. Secondly, there is absolutelty NO reason to run #10 for a lightly loaded circuit in a shed. Copper is brutally expensive at the moment and wasting cash on UF or # ten is not something most of us have the luxury of doing. I have never had a failure of any underground conductor in a NM conduit, I have repaired countless failures in UF, USE and other "direct burial" cables and installations. Unless you are placing the cable in clean sand, or completely rock free soil, UF cable is a foolish thing to use. I do some repair work at a campground that has miles of UF and USE buried. The owner is now quite clear about the fact that the dumbest thing he did, in thirty years of ownership, was direct burying electrical and cable tv cables. The shorts, opens, and low voltage issues are never ending. Last there is no requirement to install a ground rod at the end of a branch circuit. It is not an common practice, and if it's not done properly, it can lead to a situation of a difference of ground potential, which WILL give you a shock. This is why the code now required a four wire feed for a sub-panel installation. Last, given a lightly loaded branch circuit, #10 wire would be good for a run FAR in excess of 150', in fact I don't waste time doing calculations for any 20 amp. branch circuit until the last device is located in excess of 175' from the branch circuit overcurrent device. But, hey as you can tell, I'm clueless, four years of electrical engineering and decades on the job, sorry I wasted your time.

Such questions are very difficult to answer properly.

Using the same trench will depend on local codes, and enforcement of such.

To know what ga wire to use, you need to know 3 things:

Distance from the breaker box you are coming from, to the breaker box in the barn you are ending up in. The longer the distance, the bigger wire you need, to prevent voltage drop.

The amount of watts you want to use - easier to state the volts & amps you will need. If you want 220v, or just 110v, and how many amps you need to use. (You kinda hint you hope to only use 20amps, 110v...)

What kind of wire you are using - copper or aluminumn. Generally aluminumn is much cheaper for main runs, but it can't handle as much juice so it needs to be a size larger. Which is still cheaper than a copper run.

Without knowing these 3 things, _no one_ can give you a good useable answer.


If this is any distance at all, I would suggest using a good fat wire. Voltage drop can be very hard on motors. Go to Google, search for 'Voltage Drop Calculator' and you can enter the info & get a free reading of what size wire you need.

Properly ground the barn box - with a ground rod, or you may need to run a true ground wire from the house box all the way to the barn.

Consider your needs carefully. Will you ever want to run heat bulbs, water thaw, welder, or other high-draw things out there? Doing this right the first time will save a lot of headaches & extra expense later. It usually costs very little extra to run a 220v run over the 110v run, and this provides you 2x the power ot there. That _sure_ is nice to have. We always see to expand our needs once we start such a project.

Please let us know the distance you are running the wire, so we can better guess what size wire you need. Personally I don't think 12ga will be enough, but I'm only guessing like everyone else....

--->Paul

As Paul mentioned, there is no way to answer this without knowing the length of the wires and the total load, per code.

+1 on running conduit. It offers so much possibilities down the road. I also don't care for UF much for the same reasons listed above.
I would run a 1" to even a 2" conduit now, if I was only running a 12/2 romex through it. You may not think so know, but you will want to have more power later on down the road.

I agree with Paul and WisJim, but given that, this is what I did to run power to my garage:

I placed a 40 amp (220) breaker in my house's electric panel just for the garage feed. From the main house panel to the garage I used 10-3 cable that was specifically made to run underground; however, I still incased it in black plastic pipe to better protect the wire. Inside the garage, I added a sub panel with two twenty amp breakers. One breaker fed the lights. The other fed the outlets. I also grounded the sub-panel. It has worked fine for several years. The longer the run, the more power loss, so plan for that. I would recommend copper wire.

I have always run the well pump power and water supply/feed line in the same trench. Again, I always incase my wire in black plastic to better protect it.

Good luck and be safe.

Technically, to be with code allowing for motor stars & other such, and to keep your fire insurance in force, you should either replace the 40 amp breaker with a 30; or you should have used 8ga minimum copper wire.

14 ga - 15amp curcuit
12 ga - 20amp
10 ga - 30 amp
8 ga - 40 amp
6 ga - 50 amp

(Longer runs will need thicker wire, & real short runs of 5-6 feet can get by one size smaller sometimes......)

I'll bet it works for you just fine, no problems. I doubt you ever use the full 20 amp of lighting, and don't load the wires full for more than a motor starting.

But, according to some charts & codes, ever your pretty nice setup isn't quite right yet.

Not picking on you, sounds like you did a real nice job.

--->Paul

Ramblin wreck, I don't want to nit pick, but 10 gauge cable is only good for 30 amps. I would change that breaker in your main panel to a 30 amp breaker to protect that cable from possible overload. 8 gauge is the proper size for a 40 amp breaker.

ok, i know nothing compared to you guys, but a year ago i started researching running power to my outdoor sheds. i went to a website and was reading page after page of codes and i seem to remember the need to ground at each shed. that made no sense to me and seemed rather excessive.

Thanks Paul. You know, I think it may have been 8 guage. The darn stuff was awfully hard to work with...well, for an ametuer anyway.

I had 50 amp sub panel put in the barn. From the main panel box is about 200 ft.
Underground cable for that is 6 ga. underground cable as required per code. It's not cheap either.

Romex should not be used underground. It is for dry locations only. All underground installations are ( by code) considered wet. Romex installed in conduit underground will eventually fail from water deteriorating the insulation. If you have a trench free of rocks I'd go with 12-2 uf cable for the small loads you mention.

the biggest mistake I have made is to direct bury wire,

USE A CONDUIT. and if you want to add or change some thing you have a easy path to pull through,

not long a go, I went to Home depot, and was pricing conduit 2" pvc was better priced than 3/4 emt, conduit,

if you put in 2" pvc, you will have plenty of room for most any future needs,

also consider placing a second conduit in for any possible low voltage wiring , close circuit tv, (to watch animals in birthing), intercoms, telephone and with the way things are changing, who knows what the next "need" will be.

I too have had a bad time with direct bury.
its OK... it does last. its impossible to dig up andd not nick it.... especiaally after about 10 yrs and you forget where it is

I dont think electric conduit has to go as deep as a waterline. I run a new service line into my house (about 50 feet) and used really big plastic conduit. I burried it about 18" deep.

the distance is the main concern to be addressed.

I ran 150 feet of plastic conduit above ground to my house next door to run cat5 cable thru.
it runs along a fence line. out of the way... but thats only protecting cat5 cable..not a power liine.

I wouldnt put water and electric togetheriin the same ditch, digging one or the other is a PITA enough without having to worry about cutting a power line in a ditch full of water.

if it isnt far.... you could sink a telephone pole and go overhead.

I ran 2 wires 12 gauge with a ground to my barn. I put the receptacles on one 12 gauge with ground and the lights on the other one. THis was UL approved wire for underground. To my garage I ran four 4/0 so I could wield.

Wow! Thanks for all the replies, now I am truely confused ;).
It is approx. 200 ft from house to barn. I'm thinking of the most I'll need and here goes: there will be 10 light bulbs (long life twisted kind = 20w), 2 outlets off which I will run an elec. drill, horse clipper, stock tank heater in winter and occaisionally a box fan in summer. I did call an electrician friend (he has the ditch witch) who is going to come out and help with the installation also. Plan is to add a circuit to the house breaker box and run that wire to the barn, I was going to use 12g wire but have learned I should use 10g so that would be a 30 amp circuit, right? Looks like I'll have to dig two separate ditches for elec. and water each - dangit. Oh, this will have to pass under the 14' driveway and so will use a condiut for sure. Never realized there would be so much to it, for the past three years I've had an extention cord and a lot of water hose running out there. :)

Hmm, interesting about the direct burial wire. My company sells a product for which UF (12-3g UF) is required, and we have lierally 100s of these installations around the area, with NO failures due to the wire itself. This is over almost two decades, btw.

My barn is almost 400 foot from our house. We hired an electrical contractor to come in and do a proper wiring up there-the barn panel is a 100 amp service. We run five circuits of lights, and have six receptacles there (so far) with plenty of space to add more if needed in the future. All wiring is in commercial code conduit, except the main line from house to barn. That is some sort of direct burial line that included a fat ground (barn also has a regular house ground). That line was easily almost an inch and a half in diameter, and is commercial grade too. Extremely expensive! But basically the same stuff used with great success up here with many large commercial products. This was just before the big jump in metal prices, and the cost on that alone was one third of the job...well over $3 a foot.

Here is a voltage drop calculator. You will find distance makes a _huge_ difference on protecting electric motors from voltage drop.

http://www.elec-toolbox.com/calculators/voltdrop.htm

Most of your cost is in digging the trench, having the electrician do the hookups, etc. One is pretty foolish to skimp much on the actual wire, a few bucks more or less won't matter 5 years from now, when you realize you need more power out there & have to throw all this away & redo it....

At the least, run 3 wires, so you have 220v out there. Otherwise you need to run a fatter wire to get the same amps out there at 110, and that just isn't worth it at all.... (220 can be split into a pair of 110v curcuits...)

To get 30 amps out there at 220v, you need 3 #6 copper wires - that's pretty common feed wire. You then get 2 circuts of 15 amps each, which gives you some options. This would be the _least_ you would want to do - or why are you bothering?

Would need 2 #3 copper wires for 30 amps at 110 - this would not be the way to go. Would probably cost you more to give you less.....

If you run 3 wires of #2 aluminumn wire you would get a 50 amp curcuit, which may end up costing about the same for the wire, and will offer you a _lot_ more options out there down the road. This would be an A+ install.

When wiring, I know it is real easy to plan for what one was doing, & just get by. But think to the future, & what might be used out there. 10 lights, if the next owner puts in 100 watt'ers (or needs heat lamps???) thats 1000 watts, hardly any room left for plugging in anything.

As long as one is going through the motions, _now_ is the time to get it right. Or else, you really didn't improve anything over the extension cord, so what's the point?

It's your money, your project. :) Not telling you what you should do.

Just suggesting it's good to plan for the future on such a project, and if one is making improvements, make sure it is an actual improvement. :)

Running #12 or #10 or anything less than #6 out there is just wasting your friend's time, and not going to give you anything worthwhile. Distance makes a difference on electrical work, and 200 feet is a fair distance. Just how it is. Cutting corners with electricity can be a real bad thing.

--->Paul

I had the farm rewired 2 years ago, 10 buildings, 60 amp to each with 200 amp available at several juntion points around the place. Basically a 90 foot run to the house, and 3 branches of 300, 400, & 500 feet.

The direct burial wire, 3 strand, was a little fatter than my thumb per wire.

Major cost, but what does one do? And sure glad it was done back then, costs don't seem to go down! If you spend the money, do it right. Why bother if you use small wire & the lights dim, drill runs slow, wires get hot, can't use the welder you wanted to buy after you are done.... No point to that type of work.

Distance is the big thing with electric runs, just like running plumbing, if you make the pipe long enough the pipe needs to be bigger to make up for the distance & surface drag of the water on the pipe walls.

--->Paul

No help with the electricity, but take pictures of the location of your trench so you can dig down to it easily later, say, if you wanted to run a T off your waterline for another location. It's pretty useful.

Jennifer

why not just put in a seperate service for the barn....