How to install underground electrical wiring (to a garage, shed or store)

It is not uncommon to want to run 120V electrical wiring underground. You may want to send electricity to your shed, workshop or garage. Another common use is as a power supply for a lamp post or an electric gate motor. Either way, you should be aware of a few underground wiring requirements in order to meet most current building codes. We show you how to install underground electrical wiring from one location to another.

Underground Wiring Requirements – How Deep Should I Bury the Wire?

The first question we are always asked is “How deep do we bury the wiring or cable?” That’s an excellent question. And the answer is that it depends on what wire you’re using and whether you’re running it through conduit or not. Since most people ask the question in order to fulfill a particular desire for maximum burial depth, let’s start there. Depending on the depth of burial of the underground electrical wiring when installing it, we have the following options:

24 inch burial depth

  • Use Direct Burial underground power cable 24 inches deep (or more). You do not need to use conduit at this depth with UF cable, however, you must provide PVC conduit on your vertical feeds from 18 inches.

18 inch burial depth

  • You can run THWN-2 conductors inside PVC conduit just 18 inches deep in the ground. This protects the wire from damage in case someone digs over the cable. THWN-2 is basically water resistant THHN (High Heat Resistant Thermoplastic Nylon Coated Yarn)

12 inch burial depth

  • At 12 inches deep, you can run a GFCI protected direct burial power cable. Protect it with PVC where it appears in the house, garage or store.

6 inch burial depth

  • If you are using galvanized rigid EMT (electrical metal conduit) with individual conductors inside, you can bury it only 6 inches deep. The idea here is that the EMT can withstand a spade or other significant potential cause of the wiring shorting.

General Notes on Wire Burial

If you ever want to use EMT metal conduit instead of PVC, you can. Typically, we use 3/4 inch gray PVC for a single line. Also, while the required burial depths listed above should generally be accurate, check local building codes first. You want to be absolutely certain that you are in compliance before you start. We generally prefer to use PVC conduit when supplying power from a remote location underground. This gives you much more protection compared to long term direct burial cable.

In the end, just understand your options and take the safest or easiest route depending on your situation. If you can get by without conduit and the wiring is in an area that won’t interfere with future digging, then direct burial cable might be preferable. If you’re running in the middle of your yard, PVC or metal conduit might seem like the best bet, even if it’s overkill.

Underground Electrical Wiring Installation Steps

We don’t provide a ton of steps to install underground electrical wiring. Installing the wiring or conduit requires a lot of work, but not a lot of detailed instructions.

Call before you dig!

Remember to plan ahead and call before you dig. You don’t want to hit buried water pipes, power lines, sewers or anything else. In most municipalities, they will check your property within a day or two for free and when you call. Marking critical lines with flags before you start really saves you a lot of hassle and headaches. Do not skip this step!

Dig the trench

We dug a lot of trenches using shovels. Don’t do it if you value your time. If you have someone you desperately want to torture, or if you’re only going several yards, then using a trench shovel works great. However, if you have to travel a good distance with your buried electrical cable, we recommend that you rent a trencher.

Use a Toro trx300 walk-behind trencher to install underground electrical wiring

You can rent a 24-inch slicer in most places for less than $200 a day. You can even pay less if you only need it for a few hours. It saves you countless hours and hassle, so if you can afford it, buy one from your local tool rental store.

Using the trencher, plan your route and dig the trench where you plan to run your direct burial cable or PVC pipe.

Cut your entry or exit holes

Cut your exit and entry holes from the starting point (eg your electrical panel) to the end of your run.

Bosch Bulldog GBH18V-26DN hammer drill

It is helpful to use what is called a PVC conduit outlet body (LB).

LB PVC Conduit Outlet Body

These facilitate feeding the wire into a building (either the source or the destination garage or workshop). Simply remove the plate using the two screws and feed the wire as needed without having to worry about making a sharp right angle bend at the entry point.

Pro Tip: Use a heat gun to bend PVC conduit if you need to make a bend to get against the house, garage or workshop with your pipe.

Feed your yarn

Many times you can just push your cable through minimal PVC conduit. If needed, you can use metallic tape or even draw a pull line through the pipe and use it to pull the wires a long distance.

Southwire SIMPull fish tape for installing underground electrical wiring

Complete your conduit connections and fittings

After pulling your wire, make your connections to the electrical panel and complete your conduit fittings. This includes attaching the plates to your PVC conduit outlet bodies. Test your run and congratulate yourself on a job well done!

Final Thoughts

Nothing beats the essential power supply of a shed or garage. Tackle this type of project with gusto and reap the benefits. As always, consult or use a licensed electrician if things seem beyond your level of expertise.