What size feed wire for outbuilding

[RKJ]

I need some help,y'all. I've got a portable shed that I want to run power to. It's got 6-8 outlets and I plan on running a window AC unit in the summer and either a baseboard heater or a Thermostat controlled heater (plug in) in there. I've got at least 100 feet from the pole to the building to run the wire. I've read and talked with people and am still confused. I am going to run the wire underground and plan on using conduit. I understand that I need Schedule 80 pipe for electrical but am not sure of what size for sure. I was told at Lowe's that most in the area are using 4,4,6,2 aluminum but have been told by a friend of mine that is overkill and don't need that large of wire. I'm also being told that if going into conduit I could use wire that is not sheathed for underground, (in the air wire). I don't want to waste $$$ but I also don't want to run the risk of electrocution either. Also, how deep must I go? I've been told 18 -24" to 4 feet (I got 4' from the DIY magazine site. Yikes.) I live in a rural area so there is no inspection, so I'm assuming NEC guide rules.(?) Thanks all, Joe

[Preacher Jim]

Joe with the things you listed I would use 4-4-6-2 an use conduit glued at joints to keep moisture out 18-24 would be fine that way and you would be safe. Conduit because animals and tree roots can damage insulation on direct bury wire.

[Lloyd Smale]

To be legal its has to be 100 amp and that requires a #2 aluminum or #4 copper conductor. At least here. If you plan electric heat and Ac id buck up and go 100 amp. that way if you even want to drag a welder out there or add other electrical things your good to go. Code here is underground is underground be it in a conduit or not. Wire in a conduit actually has less ampacity because of heat. Contact with the bare ground cools the wire and allows more amperage. Now would I put it in conduit. YUP! If you have sand or top soil with no rocks your can get away with direct burial. But I spend my career as an electrical lineman and have seen underground go bad for no reason. Well actually there probably was a reason. It may have had the insulation nicked at the store or while you were burying it. It may have had a flaw in the coating right from the factory. Ive also seen direct burial in rocky areas that are 30 years old and work just fine. Its a matter of if you want to roll the dice. If it does go bad it sure easier to push or pull a new piece threw that conduit then dig a new trench. A ideal set up would be #4 copper in electrical conduit and a 100 amp main pannel. We installed MILES of it that way. never once glued anything. the conduit seals up just fine (unless you want to cross a lake) just by putting them together. One thing to keep in mind though is your getting advice from people who don't live in your state or county. there are electrical codes in you county. they are not BS they are there for good reasons. Id suggest you go to the inspectors office and find out what is code in your area and do it right. they are there for your safety and reliability not to punish you.

[kmrra]

If you are doing it your self , I would just go with #8 , you will find that 4462 will get rather expensive at 100 tf , I used it on my house ,and I needed it there but that was over 600 bux for that , not counting trenching .....an out building # 8 is all you will need , that will carrie a welder no problem

[OS OK]

"Cheap huh? Down and dirty cause nobody's gonna look at it! Nobody's gonna know."
How many times have I heard that spew when I'd go to give an estimate?
After an hour of consultation and talking some common sense into them, explaining things...they still wanna cut some corner somewhere to save a few bucks? Most of the time I'd end up walking off with my head shaking...dealing with the homeowner is the one big thing that pushed me into Heavy Industrial Electrical...well besides the money being a lot better and the work more interesting.
Wheres the satisfaction in doing a thing right anymore? Gone with the wind...I guess?

[rancher1913]

I have never heard anybody say "I wish I had used smaller wires".

[lightman]

Two important parts of voltage drop calculations are load and distance. If you give more info I can figure it for you. Lloyd is right about a 100amp service being the minimum that the National Code recognizes, but that is for a service from a utility with a meter installed. For your purposes you're talking branch circuit. It can be whatever size that is adequate for your needs. A quick calculation shows that you can get 60 amps available with an acceptable voltage drop using #4 coper in 1-1/4 inch conduit with an acceptable voltage drop. 60 amps would run your A/C or heat, lights, most small power tools (1 or 2 at a time), maybe a small air compressor. Or a lead pot!:grin:

There are some arguments concerning using conduit vs not using conduit. Conduit cost more up front. There is more work to install conduit and pull wire than it is to lay direct burial wire in the trench. Conduit protects the wire from damage. Tree roots, rocky soil, construction trash, ect can damage the wire. If the wire should ever fail in conduit its sometime possible to pull the old wire out and pull in new wire without having to dig your yard up again. Schedule 80 is required above ground but the lighter and cheaper schedule 40 may be buried. 24 inches is the preferred depth unless there is a reason to go deeper.

There are several ways to pull wire in conduit. You can stretch the wire out on the ground and slide the conduit over it as you roll it off into the trench. You can install the conduit and pull the wire with a fish tape. You can install the conduit and blow or vacuum a string through the conduit to pull the wire with.

There are several ways to wire your building also. I would install a small breaker box, say 6 or even 12 places, run the branch circuit wires to this box, then add receptacles and lighting on smaller circuits.

I would be happy to make any calculations that you need. Make a list of the things you plan to use and PM me if you want.

[w5pv]

After losing everything to an electric fire I have a tendency to over wire and go with the smallest breaker that will hold the operation,besides having to reset the breaker at time I have had no other problems.

[dragon813gt]

This is IMO. When it comes to trench depth I dig below the frost line for everything. This prevents a whole host of issues. The depth is going to vary by region. In my area it's 36". I have no problem digging that deep if it's going to prevent issues in the future.

Wire size will be determined by what size panel you're putting in. 100 amp is the minimum I would put in an out building. Larger service will have larger wires. I personally don't like Aluminium wires and will pay for copper ones. I've had to many issues w/ aluminium wires over the years. Last thing I'd ever do is bury them where I can't get to them easily.

There is a reason there are codes. Use them as the minimum acceptable. Exceeding them won't hurt anything. Unless the wire is to large to fit in the breaker terminals.

[rda72927]

I have never heard anybody say "I wish I had used smaller wires".

No, I haven't either. But I have heard, "I used too small gauge wire. Guess I'll pull it again"

[Plate plinker]

Wire and cable your way. .com

buy from them some thhn wire and pull it in conduit. Conduit is cheap buy it oversized.

[Teddy (punchie)]

I would use conduct to get you below ground first 3 feet. If you have soft soil no stones then leave out conduct the rest of the way. If you think your going to damage wire use conduct.

I would run 2 2 4 4 USE cable and run 60 Amps to 100 Amps , Make sure you use a snake or string (rope) to pull cable (wire).

Conduct can be metal.

plastic conduct pipe must be gray in color, So maybe cheaper for you to get water pipe and spray it gray. You said no inspection, so you can just make sure it is the right size. I make sure I place caution tape in above wire I bury.

better to go a size or too large then too small.

[lightman]

There is no minimum size for an out building unless you put a separate meter on it. Its considered a branch circuit and can be anything from 15 amps up to whatever you want. The reason that conduit is gray is because it is UV resistant. If you bury it, water pipe will work but for the little cost difference, I don't see the reason. I see no reason to paint it. The frost line is worth consideration, not a problem where I'm at!

[popper]

If going through the existing panel, gotta figure that load onto the mains. 100' branch circuit is good for 4 outlets!, not 6 or 8. Gluing the joints tends to reduce groundwater influx. You also need to consider the remote earth ground situation.

[jonp]

I'm a believer that all wire in the ground should go into a conduit. You never know who is going to dig a hole for a new tree.

[Duckiller]

Put the wire in a conduit. It protects it and if you do something bad or need a bigger wire you can pull old wire out and replace with bigger. don't get too cheap. How long do you expect to live there? Figure your wireing cost on an annual basis.It won't seem so bad . One thing you don't want to do is wire this shed and then find out that you do not have enough power. Good luck and enjoy your new shop.

[Plate plinker]

Pull some comm wire through their too while your at it.
Make yourself a man cave.

[RKJ]

Thanks guys. I'm in Central Missouri and I have to go at least 24" deep. I figure Copper wire as I don't want aluminum, (no reason, just would prefer Copper) I don't intend to go cheap, but I also don't want to spend unnecessary money either. My concern is safety (now & in the future). We have a lot of rocks and trees in the yard and figure I would use conduit as it seems the smart thing to do. I've got the shed already wired with 6 (or 8) outlets all 110, and a 6 breaker box but I don't remember what amp it is. The guy at Lowe's recommended the box and he seemed to know his stuff. I've been told to go schedule 40 conduit and read that I need schedule 80. (?) I'm not trying to skirt any inspections but the county is not involved, if I have to (to be legal) I will get them out here. I've also got my insurance to figure so it must meet code. I'll try to go to Lowe's tomorrow and see what sizes of wire they have and get back with you guys. I'm still confused but not as much as before. :) Thanks again. Joe

[KYCaster]

I need some help,y'all. I've got a portable shed that I want to run power to. It's got 6-8 outlets and I plan on running a window AC unit in the summer and either a baseboard heater or a Thermostat controlled heater (plug in) in there. If the outlets are rated for 15 amps, you can get by with a 15A single pole (110V) circuit breaker in your existing distribution panel. Over 100', increase one wire size to 12ga. You could probably run a small AC and maybe a couple of LED lights, but you'd have to turn off the AC to run anything else, like a table saw or casting pot. Heater would be iffy. I've got at least 100 feet from the pole... Pole? Is your meter and main disconnect on a pole outside the house? If so, adding another disconnect and distribution panel here would probably require a larger capacity service and inspection. If you plan to feed the shop from a circuit breaker in your existing panel, does your service have the capacity to handle the additional load? Do you know how to determine that? to the building to run the wire. I've read and talked with people and am still confused. I am going to run the wire underground and plan on using conduit. I understand that I need Schedule 80 pipe for electrical... I've seen this on the 'net before and I'm at a loss to explain it. Only thing I can come up with is, PVC conduit is gray and Sch80 plumbing pipe is usually gray. AFAIK plumbing pipe is not approved for wiring. but am not sure of what size for sure. I was told at Lowe's that most in the area are using 4,4,6,2 aluminum but have been told by a friend of mine that is overkill and don't need that large of wire. Depends on the load you plan for. I'm also being told that if going into conduit I could use wire that is not sheathed for underground, (in the air wire). I don't want to waste $$$ but I also don't want to run the risk of electrocution either. Also, how deep must I go? I've been told 18 -24" to 4 feet (I got 4' from the DIY magazine site. Yikes.) I live in a rural area so there is no inspection, You may be able to get the work done without an inspection, but why would you want to, especially after you've gotten so much conflicting information. Ask your insurance agent what he thinks. so I'm assuming NEC guide rules.(?) Thanks all, Joe

Dude! You need to hire an electrician! (Not the one the guy at Lowes recommends)

Good luck
Jerry

[lightman]

A 6 circuit box is probably rated at 70 amps. A few are rated 100 amps. Thats the max that it can carry, not what you have to supply it with. If this was mine, I would consider 3 #4 copper wires in 1-1/4 inch conduit fed with a 60 or 70 amp breaker and drive a ground rod at the building to ground the panel. Go schedule 80 pvc above ground and schedule 40 below ground. This would do most anything that most would want to do in a home workshop. This would run your heating/ac unit and lights, plus a welding machine, air compressor, most any power tool and most any bench tool. Maybe not all at once.

If you want to go bigger, 3 #2 copper wires would most likely do more than you would ever want, fed with a 100 amp breaker. They would fit in the 1-1/4 conduit but I would probably bump it up to 1-1/2 inch just to make the pull easier. You could use aluminum to save some money but I recommend against it. With aluminum, bump it up at least one wire size to get the same amp rating. This may require a size bigger conduit also. My offer is still good if you want to PM me. I did this for nearly 40 years and my advice is free!

I can't argue with the advice to hire an electrical, but at least you know what to ask for.

[leeggen]

How big of an out building are you talking about??? have seen guys build a 100 X 100 and have very little in outlets in it,and have seen guys build 10 X 10 and have twice as much inside it. You need to think about what type equipment you are going to use in the building now and posibly in the future. Then and only then can anyone figure what you need for a load center and wire to match. I don't know what your tallents are so I can tell you what DIY you can do. You have been given some good advice to just hire the wiring done and the electrician will fix you up. Yers you can save a few bucks by possibly doing the trenching and the conduit provided the electrician will agree. Good luck with whichever way you go.
CD

[RKJ]

The building is 12x 24, I've got friends that are contractors so that part is covered. I've got either 6 or 8 outlets (I don't recall the exact number). I asked the forum as I was getting told different opinions. Thank you for the feedback.

[KYCaster]

The building is 12x 24, I've got friends that are contractors so that part is covered. I've got either 6 or 8 outlets (I don't recall the exact number). I asked the forum as I was getting told different opinions. Thank you for the feedback.


So now you have an additional 18 or so internet opinions, worth pretty much exactly what you paid for them, and still no clear answer.

Do yourself a favor and hire a competent electrician.

Jerry

[Eddie Southgate]

So now you have an additional 18 or so internet opinions, worth pretty much exactly what you paid for them, and still no clear answer.

Do yourself a favor and hire a competent electrician.

Jerry

This is what I would do as well as have him pull an extra cable. It cost more but it's awful nice years down the road when the one your on goes bad and you can just unhook it and hook the other one up and be back in business .

[GL49]

So now you have an additional 18 or so internet opinions, worth pretty much exactly what you paid for them, and still no clear answer.

Do yourself a favor and hire a competent electrician.

Jerry
The last sentence is a good idea. That's what you've got.....internet opinions. I am an electrician, teach the NEC and it's practical applications at the local community college, sit on the local apprenticeship board, and have been doing so for quite some time. Some of these answers aren't quite right, and no, I'm not gonna get into a fight and tell you which ones. If you want to do this yourself, employ the services of a contractor and ask what you can do to help cut costs. I doubt he'll be willing to stick his neck out and give you advice. I sure wouldn't. Yep, this is just another internet opinion.

[SSGOldfart]

Remember you'll want to go at least 1/2 size larger on your conduit because a 100' of wire is going to be hard to pull through it, and no more than 4 bends,look for long sweep 90's aka elbows,if possible you want to come into your sub-panel from the bottom or back with out a turn( makes wiring easier) what size breaker do you have on your service,to feed your sub-panel, your wire size needs to be sized by the load and feeder. Most likely THHN #4/4/6/8 will handle it.

[RKJ]

Thank you to all that posted, I don't intend to do anything unsafe and if I have to get a licensed contractor I will. Most of the people on this forum are DIY types (so it seems) and I doubt that many of you would not think that you couldn't do this yourself. I asked for help here as I've found a lot of experienced people on this forum willing to help someone out. I appreciate the help that has been offered, and will get this done. Thanks again.

[Lloyd Smale]

Electrical work isn't a black science. Its pretty basic. Just do it right and don't cut corners. You sure don't need a 100 dollar an hour contractor to do something as simple as you plan. Best advice though is to go and see your local inspector and discuss it with him, find out whats code in your area and use that as a minimum.

[Wolfer]

A 6 circuit box is probably rated at 70 amps. A few are rated 100 amps. Thats the max that it can carry, not what you have to supply it with. If this was mine, I would consider 3 #4 copper wires in 1-1/4 inch conduit fed with a 60 or 70 amp breaker and drive a ground rod at the building to ground the panel. Go schedule 80 pvc above ground and schedule 40 below ground. This would do most anything that most would want to do in a home workshop. This would run your heating/ac unit and lights, plus a welding machine, air compressor, most any power tool and most any bench tool. Maybe not all at once.

If you want to go bigger, 3 #2 copper wires would most likely do more than you would ever want, fed with a 100 amp breaker. They would fit in the 1-1/4 conduit but I would probably bump it up to 1-1/2 inch just to make the pull easier. You could use aluminum to save some money but I recommend against it. With aluminum, bump it up at least one wire size to get the same amp rating. This may require a size bigger conduit also. My offer is still good if you want to PM me. I did this for nearly 40 years and my advice is free!

I can't argue with the advice to hire an electrical, but at least you know what to ask for.

Im a journeyman electrician and this is what I would do for myself.

[Lloyd Smale]

cant argue much with that post either other then that going from copper to aluminum usually means jumping up 2 sizes. #6 copper will replace #2 aluminum and #4 copper would replace 1/0 aluminum

[Teddy (punchie)]

Maybe hard to find underground rated COPPER.

Under ground THHN , maybe if they have changed it but the old THHN rating is not for use in underground conduct.

UF OR USE2 , older was USE rating .

I seen AL in the ground for many years with no trouble.

[RKJ]

The electric company is coming out next week to replace the fuse box that is on the pole right now for a CB type (100 Amp) and then I've got to dig the trench and get it installed. Hopefully by the end of the month it'll be wired. I forgot to mention the size of the shed, it's only 12x24 and will be more of a reloading room than a true shop. Thank you all again for the help.