Outdoor Electrical Wiring

[weldingisfun]

Can anyone tell me what would be the longest run I can do off of a 20 Amp breaker using 12-3 outdoor wire. It is for lights in a goat shelter located approximately 350 to 400 feet from the breaker box.

 

[kenstrac]

Go here and put in the numbers you have.

Voltage Drop Calculator

 

[mbohuntr]

You need to consider the resistance of the wire in calculating the current. I have been told that a rule of thumb is to increase the wire by one size for runs over 100'. So I'm thinking that 10-3 is in order. And I would also use UF type and either bury it in conduit, or deep enough to protect it. Whatever the NEC says.

 

[DennisArrow]

Hey.....I know you will hear about this from the doom and gloom crowd that will insist upon spending your money for you and surely not coming out to help you do the job. SO.....here goes.........

Am in almost the same exact situation. Goat barn/shed 300 feet from the house. Needed lights, fence charger, outlet for hair dryer for the kids, heat lamp, water warmer for low 20's, and maybe a charger for spotlight..............

300 feet from the breaker box. Rented a ride on trencher cause I had to go through MANY tree roots on the way. Ran 12/3 underground cable on a 20A breaker. NO problems. The breaker has NEVER popped.

Since running the circuit, have built a barn on the sight with the same circuit wired in.
This added a small dorm type fridge and 3 florescent fixtures to the mix. Yes, my wife, who's operation this really is, is judicious in using amperage. In other words she doesnt try running the hair dryer and the 3 water warmers at the same time; but everything else, lights, fridge, fence charger, and spot light charger WORK JUST FINE with no breaker blowing............

NOW........if I was to do it again............a 30A with 10-3 would be worth the extra money to be able to run everything........BUT......common sense does prevail.

At the same time, I ran to another barn where I park the Air Stream trailer. At first I used the 20A 12-3; but noticed when I ran the AC or heat pump that the wiring would be warm.....NOT HOT.........but a definate voltage drop.........Redug the trench, put in 10-3 on a 30A breaker.......NO VOLTAGE DROP and NO cable getting warm...........

So..........Again, if I had to rewire the goat barn/shed power feed, which I will one of these days when there is a problem.......I WOULD USE 10-3 on a 30A............God Bless.....Dennis

 

[mbohuntr]

Thought that's what I said??? Problem with voltage drop is not only that the wire gets hot, but that 'spensive appliance that wasn't in the origional plan,( but that someone added later cause there was power out there) and will burn itself out costing you more. (brown outs) Extra capacity never hurts, and hot wires start fires...

 

[EddieWalker]

Why 12-3? For lights, all you need is 12-2, unless you are wanting to have a three way switch at either end of the run.

The calculator says you will loose less then a quarter of your amps over the run, which leave you with over 15 amps to work with.

A 100 watt light bulb will pull 1 amp, give or take. It's an easy rule of thumb. How many lights do you plan to have and how many amps will they draw? If you have five 60 watt bulbs, you are only pulling 3 amps.

The breaker will trip when you pull more power then available. Don't go to the full 15 amps, or you will trip the breakers. Figure out your load in how much light you need and if you are under or around ten amps, you will never have a problem. The closer to 15 that you get, the more likely you will be to have issues.

For just lighting, you won't have any problems at all.

An example for me is that I have three 75 watt lights along my driveway and two cairrage lights at my gate on a 12 gauge wire. My total amp draw for those lights is 3 amps. My driveway is 700 feet long. That calculator said that I'm loosing 40 % of my 20 amps to the line, so I still have plenty to run those lights, which work great every night.

Eddie

 

[mbohuntr]

Thanks Eddie, your right. My concern was that they are using a breaker that is rated for the wire size, not for the application. Dennis mentioned that a heater and hair dryer etc were added after the fact, and a different user in your setup might not realize that it was not rated for a weedeater etc. If you didn't place outlets there, your good to go. I was only anticipating the likely uses down the road. I also missed the 12-2 part. that would save a lot of money!! good tips. My road lights were sized at 10-2 because the electrician I consulted asked me if I was placing outlets at the road end.

 

[EddieWalker]

As for the outlets, it really depends on what he's using and if it's at night when the lights are on. If it's during the daytime, he'll still have 15 amps and should be able to run most anything. It's a short enough run that his power drop is minimal. I'd put a couple outlets out there just because they are cheap and handy to have if needed. More then likely, he'll rarely use them, but you never know.

On mine, I mentioned that I have a 40% drop at my gate to power my lights. I put in an outlet there and have run my cement mixer all day long, and also my metal chop saw to cut cultured stone. I'm not sure what I'm pulling with those tools, but with the lights off, I'm able to get away with it. While I agree that I'm pushing things, the worse that can happen is that I trip the breaker and have to walk 700 feet each way to reset it.

Eddie

 

[dave1949]

With any cable, it would be a good idea to provide a grounding rod at the shed. Tie all the green connectors on outlets and fixtures together and run that to the grounding rod. This is really important if you are not carrying an earth ground from the subpanel to the shed.

Dave.

 

[20 20]

I've been there and done that, small wire works good for temporary. If you plan on using more power draining things or want better results BIGGER wire is better. Eddie also made a good point why not 12-2. If it were me I'd go with no less then 10-2 because of heaters and blow dryer. Just remember a buck saved now may cost more later???????