OT - Electrical question

[CB in central NY]

I would like to run an electrical line from one barn to another. The object is to power 3 lightbulbs, 4 outlets, an air pump motor, and a hay elevator motor (of course, not all at the same time). I would like to run a 30 amp line.

The distance between barns is 150 feet. Once there, I plan to branch out from the breaker panel using 12-gauge wire for the lights and outlets.

What gauge cable would I need to cover the 150 feet? I have some leftover 10-gauge copper cable and most calculators give me about a 9 volt voltage drop over that distance. Should I go with something larger like an 8 or a 6?

Thanks in advance for all answers.

 

[Walt Davies]

I run 10/3 with ground direct burial cable to my barn with 30 amp breakers, it run every thing that I want an is over 100 ft.
Walt

 

[Anonymous-0]

CB looks to me if your not gonna run them all at one time it wont matter much. But if you ever run alot at one time you would need a larger gauge because the wire would get too hot. I have run some about 200ft before.

 

[Mike (WA)]

Most electrical supply stores will have books that give this kind of info- would be better than guessing at it, and getting it wrong, with disastrous consequences. Without looking at my book, (which is where I ain't, at present), 10 guage seems small.

 

[Anonymous-0]

First realize the electric loads tend to grow, you add more than you started with.

Second remember that unless you have special motors (repulsion start, induction run) the starting current is 6 times the running current. If you have 9 volts drop at running current, you will have 54 volts drop at starting. That motor will take so long starting that it will likely burn up and will do a poor job handling tasks that require short bursts of peak power. And with the terminal voltage 9 volts low, the motor current will be 8% high for normal rated load. An induction motor hasn't the privilige of taking less power when the voltage is low, the AC motor maintains a near synchronous shaft speed and so the shaft load is the same no matter what the voltage (within reason) and the motor with a low supply voltage has to draw more current to run the load. Low voltage tends to be the death of motors.

Third, its a lot harder to put the wire in place than to buy it larger so its generally easier in the long run to put the wire in once and to make it large enough.

In my machine shed I set up a woodworking shop 60' from the 200 amp service entrance. The outlets are wired with #12. Running a shop vac and radial arm saw on the same circuit, it took the radial arm saw 5 or 6 seconds to get up to speed. I ran a #10 extension cord from an outlet mounted at the service panel. That improved things but then with both of them starting on the same circuit, I tended to trip the 20 amp breaker either while starting or while sawing. I have a 50 amp 4 wire circuit for welder or whatever, running the length of the building so on the shop end, I hung a temporary 100 amp panel and wired outlets to it so I and put saw and vac on separate phases and I run a SHORT #10 over to the saw. Now it gets up to speed in a hurry, without showing 25 volts drop while starting. I wired the saw table with a relay to run the vac so the vac always starts when I start the saw. I can get a lot more work done, but the run to the 50 amp 4 wire outlet is #6.

Being cheap on wire size is bad economics, worse after the first motor burns out from the low voltage.

Gerald J.

 

[John T]

CB, Yes, you should go with at least 8 gauge (if copper or bigger if aluminum of course) considering 30 amps of service at that distance and NO the 10 gauge could be problematic due to excess voltage drop (despite the charts cuz one should allow room for expansion) if n when you start runnin motors due to the extra start up current like Gerald mentioned. I take it your just running 120 volt only??? You can go with direct burial UF cable but if you run under any driveways etc. enclose the wire in conduit.

Theres a long winded discussion of the safety and importance of equipment grounding conductors over on

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=toolt&th=197247

John T
Electrical Grounding

 

[Anonymous-0]

Well shoot CB, you did not tell us total load, type of insulation, dry or wet location, single or multicore conductors.
They say figure for 125% of continuous load. The sum of the noncontinuous load plus the continuous load if the service-entrance conductors terminate in an overcurrent device where both the overcurrent device and it's assembly are listed for operation at 100% of their rating.
There is a lot of mess you can get into with motors and such, but John is pretty much right on. At least 8 GA. wire.
Remember to protect it well if buried...or get it up in the air so tall equipment won't hit it...don't ask me how I know.
Best of luck...and be careful.

 

[Oldmax]

I would use at least #6 Entrance cable over head or #6 underground 240 volt. Making sure that you use breaker box in building . that would give you two 120 volt circuits it building.

 

[dave guest]

I go with Walt. Unless you live in it, #10 service will go a long way. Lotta houses in Detroit still run on 30amp service, usually 110volt. I use #10 at 100 feet for a welder, compressor 4 horse, lots of lights, grinder, drills. One person shop, though. Put your #10 in conduit and if you want bigger later, pull some more in. Licensed master electrician and contractor for 25 years.