Licensed electricianFamily-owned in Greeneville, TN
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Electrical guide · GPM Electrical
To run power to a detached garage or shop, you run a feeder from your main panel to a subpanel in the outbuilding, then wire the circuits from there. The right size of wire and breaker depends on what you plan to run, how far the building is from the house and whether the feeder goes underground or overhead. A permit and inspection are usually required. This guide covers the decisions to make before anyone digs.
The most important question is not about the garage. It is about the tools and equipment that will go in it. A garage with lights and a few outlets needs far less than a shop with a welder, a compressor, a table saw and a heater. Write down what you have now and what you might add in five years. It is much cheaper to size it right the first time than to dig the trench twice.
This is the set of wires that carries power from your house to the building. Its size depends on the load and the distance. Longer runs often need heavier wire to keep voltage from dropping. We size it to your actual plans.
A subpanel is a smaller breaker panel in the garage or shop. It gives you a main shutoff in the building and room for its own circuits. Detached buildings typically need a subpanel set up with separate neutral and ground connections, and it needs its own grounding. This is one of the places a do-it-yourself job often goes wrong.
Most feeders to outbuildings run underground in conduit or with cable made for burial. The trench has to be a certain depth, and the depth depends on the type of wire and conduit. Overhead is sometimes an option, but it brings height and clearance rules. East Tennessee soil can include rock and roots, so the digging is part of the price.
Lights, outlets and larger loads each get their own breakers. Outlets in garages and outbuildings generally need GFCI protection, and large tools and welders often need their own 240-volt circuits. Planning where the benches, doors and tools will go before the walls are finished makes outlet placement much better.
Running a feeder to a new building is the sort of job that usually needs a permit and an inspection. The rules vary by city and county, and some inspections happen at more than one stage, such as before a trench is filled in. Skipping that step is a risk when you sell or file an insurance claim. See our guide to Tennessee electrical permits to learn how to find out what applies.
Sometimes the limit is not the garage. If your house panel is full, old or small, adding a large feeder will not work. In that case, the panel needs attention first, and it is often smarter to do both at once. Our electrical panel upgrade service covers that side.
We have run electric to a large detached garage for a Greene County customer, and brought new service to a covered porch for another. Outbuildings are some of the most common projects we see, from garages and workshops to barns on rural property. You can see more on our garage, shop and addition wiring page.
Safety note: Do not run extension cords or small household wire to a building as a permanent fix. Do not tap into the house wiring without a proper feeder and breaker. Anything that connects to your main panel is best left to a licensed electrician.
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Not as a permanent solution. Extension cords are not made to carry loads long-term or to be buried. They can overheat and fail.
Usually yes, if you want more than a light and an outlet. A subpanel gives you a shutoff and proper protection in the building.
It depends on the type of wire and conduit, and local rules. Ask your inspector, and we will tell you what applies to your job.
We will talk through the whole job when you call, including the trench and who does what. Tell us about your property and we will say what we recommend.
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Planning power to a garage, shop or barn? Call and describe the building. We can often talk it through over the phone.
Tell us about the job and Nick will get back to you.
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