It's not uncommon to want to run 120V wiring underground. You may want to power your shed, workshop or garage. Another common use is to power a lamppost or electric gate motor. In either case, there are some underground wiring requirements you should know to meet the latest building codes. We show you how to install underground electrical wiring from one location to another.
How to Install Underground Wires – How Deep Do I Bury the Wires?
The first question we are always asked is "How deep do we bury the wire or cable?" It's a good question. The answer is that it depends on what wire you're using, and whether you're running it in conduit. Since most people ask this question for a specific need for maximum burial depth, let's start there. Decomposed according to the depth of buried underground wires during installation, we have the following options:
24" deep burial depth
- Use direct burial underground feeder cables 24 inches deep (or more). You don't need conduit at this depth with UF cable, however, you do need PVC conduit on the vertical feeders starting at 18".
18 inches deep burial depth
- You can run THWN-2 conductors in PVC conduit 18 inches deep underground. This protects the wires from damage if someone digs over them. THWN-2 is basically water-resistant THHN (Thermoplastic High Heat-resistant Nylon-coated wire)
12" deep burial depth
- At 12 inches deep, you can run GFCI protected direct buried feeder cable. Protect it with PVC wherever it appears in the house, garage or shop.
6 inches deep burial depth
- If you use galvanized EMT (electrical metal conduit) with individual conductors inside, you only need to bury it 6 inches deep. The idea here is that the EMT can withstand a shovel or other significant potential cause of a short in the wiring.
How to Install Underground Electrical Wire: General Considerations for Buried Wire
If you want to use rigid metal conduit or even EMT instead of PVC, you can. Typically, we use gray 3/4 inch PVC for the single wire. Also, while the required depths listed above should generally be accurate – check your local building codes first. Before you start, you want to be absolutely sure that you are compliant. We generally prefer to use PVC conduit when supplying power to remote locations underground. This gives you more protection in the long run than direct burying cables.
Finally, understand your options and choose the safest or easiest route for your situation. If you can get away without conduit, and the wiring is in an area that is not easily obstructed by future excavations, then direct burial cable is probably the best option. If you're running through the middle of your yard, PVC or metal conduit seems like a better option—even if it's a bit of an overkill.
We do not provide extensive steps for installing underground electrical wiring. Installing wire or conduit is a lot of work, but not a lot of detailing.
Call before you dig!
Don't forget to plan ahead and call before digging. You don't want to hit any underground water pipes, power lines, sewers, or anything else. In most cities, they'll inspect your property for free within a day or two and when you call. Marking critical lines with flags before you start can really save you a lot of trouble and hassle. Don't skip this step!
dig trenches
We dug a lot of trenches with shovels. If you value your time, don't do it. If you have someone you really want to torture, or you're only walking a few feet, then using a trench shovel will do the trick. However, if you need to travel great distances with buried cables, we recommend hiring a trencher.
You can rent a 24" trencher for less than $200 per day in most places. You can even pay less if you only need a few hours. It can save you tons of time and hassle, so if you can afford it, get one at your local tool rental shop.
Using a trencher, plan a route and dig trenches where you plan to lay direct buried cables or PVC pipes.
cut entry or exit hole
Cut access holes from the starting point (for example, a switchboard) to the end of the run.
It helps to use a so-called PVC conduit outlet body (LB).
These make it easy to run wire into a building (source or destination garage or shop). You just use two screws to remove the plate and feed in the wires as needed without worrying about sharp right angles at the entry.
Pro Tip: If you need to bend to pipe against your house, garage, or workshop, use a heat gun to bend PVC conduit.
feed your wire
Many times you can simply run the cables through a minimum of PVC conduit. You can use metal fish tape or even suck a guy line through the pipe and use that to stretch the line if you want.
Complete Connections and Conduit Fittings
After pulling the wires, connect to the electrical panel and complete the conduit fitting. This includes securing the plate to the PVC conduit outlet body. Test your run and give yourself a pat on the back for a job well done!
final thoughts
There's nothing like providing much-needed power to your shed or garage. Attack such projects with gusto and benefit from them. As always, if something seems beyond your expertise, consult or use a licensed electrician.