It’s not uncommon to want to run underground wiring to power your shed, workshop, or garage. You may also need it for a lamppost or electric gate motor. However, there are specific requirements you should know about to meet building codes. In this article, we will guide you through the process of installing underground electrical wiring from one location to another.
How Deep Do I Bury the Wires?
The first question that arises is, “How deep should the wires be buried?” The answer depends on the type of wire you are using and whether you are using conduit. Let’s explore the burial depth options based on your specific needs:
24″ Deep Burial Depth
If you’re using direct burial underground feeder cables, bury them at least 24 inches deep. At this depth, you don’t need conduit for UF cable. However, for vertical feeders, you will need PVC conduit starting at a depth of 18″.
18″ Deep Burial Depth
For a burial depth of 18 inches, you can run THWN-2 conductors in PVC conduit. This protects the wires from damage if someone accidentally digs over them. THWN-2 is a water-resistant wire coated with nylon, similar to THHN.
12″ Deep Burial Depth
At a depth of 12 inches, you can use GFCI-protected direct buried feeder cable. Make sure to protect it with PVC wherever it appears in your house, garage, or shop.
6″ Deep Burial Depth
If you choose to use galvanized EMT (electrical metal conduit) with individual conductors inside, you only need to bury it 6 inches deep. The idea behind this option is that the EMT can withstand potential causes of a short in the wiring, such as a shovel hitting it.
General Considerations for Buried Wire
If you prefer rigid metal conduit or EMT instead of PVC, you have that flexibility. Typically, we use gray 3/4 inch PVC for a single wire. While the burial depths mentioned above are generally accurate, it’s crucial to check your local building codes to ensure compliance. Using PVC conduit provides better long-term protection compared to direct burying cables.
Consider the location and potential obstructions before making a decision. If the wiring is not easily obstructed by future excavations, and you can do without conduit, direct burial cable is a suitable option. However, if you’re running through the middle of your yard, PVC or metal conduit is a better choice, even if it may seem like overkill.
Call Before You Dig!
Before starting any digging, it’s essential to plan ahead and call your local authorities. They will inspect your property for any critical underground infrastructure such as water pipes, power lines, or sewers. Marking these lines with flags can save you from unnecessary trouble and hassle.
Digging trenches manually can be time-consuming. If you want to save time and effort, consider renting a trencher. For less than $200 per day, you can rent a 24″ trencher in most places. It’s a worthwhile investment, especially if you need to cover long distances with buried cables. Plan your route and dig trenches where you intend to lay the direct buried cables or PVC pipes.
Cut Entry or Exit Holes
To facilitate the installation process, cut access holes from the starting point (e.g., a switchboard) to the end of the run. Using a PVC conduit outlet body (LB) can make running wires into a building (e.g., garage or shop) much easier. These outlet bodies eliminate the need for sharp right angles at the entry point.
Pro Tip: If you need to bend the pipe against your house, garage, or workshop, use a heat gun to bend the PVC conduit.
Feed Your Wire
In most cases, you can run cables through PVC conduit. You can use metal fish tape or a guy line to stretch the line through the pipe. These methods will help you pull the wire smoothly and efficiently.
Complete Connections and Conduit Fittings
After pulling the wires, connect them to the electrical panel and complete the conduit fittings. Make sure to secure the plate to the PVC conduit outlet body. Test your installation to ensure everything is working correctly.
Installing underground wiring to power your shed or garage is a satisfying project. Approach it with enthusiasm and reap the benefits. However, if you feel that the task exceeds your expertise, it’s always wise to consult or hire a licensed electrician.