How To Splice Underground Wire

Updated: Jan. 18, 2024

Make a splice that will last longer than the wire

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Accidentally cut an underground electrical wire? The easiest way to repair it is with an underground splice kit, which uses a rustproof connector to repair and seal the break.

Tools Required

  • 4-in-1 screwdriver
  • Lineman's pliers
  • Non-contact voltage tester
  • Spade
  • Utility knife
  • Wire stripper/cutter

Materials Required

  • Heat-shrinkable underground splice kit or Gel-filled wrap-around splice kit
  • Surveyor’s tape
  • UF cable

Project step-by-step (11)

Step 1

Assess the damage

If you’re digging holes in your backyard, you should always call 811 a few days beforehand to mark all the underground wiring. Unfortunately, privately owned wiring will not be marked, so it’s still possible to strike an electrical cable. It’s especially likely if you’re digging between the house and a freestanding garage, shed or yard light. If you do cut a power line, though, it’s easy to fix. Here’s how.

First, turn off power to the electrical device fed by the broken cable at the circuit panel. Then dig 12 in. on each side of the break in the wire and gingerly work your way to the cable. You’ll find the cable anywhere between 12 and 24 in. deep. When you locate the cable, use a noncontact voltage detector to ensure there’s no power.

If you have a broken underground line and no clue where the break is, hire an electrician with an underground open/short locator. The electrician will be able to locate and mark the underground cable, determine how deep the cable is buried and pinpoint within a few inches where the problem exists.

Step 2

Get the Right Kit

Underground AC splice kits come in two varieties: heat-shrinkable tubing and gel-filled shield. Both use a brass splicing block to connect the wires. But they differ in how they protect the splice.

The most common type of kit protects the splice with an 8-in. length of heat-shrinkable tubing filled with watertight hot-melt adhesive. Slide the tubing over the cable before you connect the wires to the splice block. Then slide the tubing over the connector and shrink it with a heat gun (best) or a torch (gently). The other type is a corrugated plastic shield filled with an encapsulating gel. It’s twice the price, but it installs much faster, is goof-proof and is very long lasting.

How To Splice Underground Wire Kit CalloutsTMB STUDIO

Step 3

Heat-Shrinkable Tubing Repair

You can use a splice block to fix a severed cable. Here’s how.

How To Splice Underground Wire Underground ConnectorTMB STUDIO

Join the wires

Insert the wires into the splice block connectors, making sure the colors match up, then tighten the screws.

How To Splice Underground Wire Join The WiresTMB STUDIO

Step 4

Seal the connection

Slide the heat-shrink tube over the connector. Use a heat gun to shrink it and seal the connection.

Replace the whole section of cable that you dug up with the same gauge UF (underground feeder) cable. Cut the cable about 12 in. on either side of the break. Then strip back the sheathing 2 in. and the wire insulation 5/8 in. Use two special underground splice kits (sold at home centers) to connect the new cable section.

Slide the heat shrink tube over one end of the cable, then connect the wires to the brass connector. Do this on both ends of the new cable. Once the damaged cable is replaced and the wires are joined with connectors, slide the heat-shrink tube over each connector. Heat the tube with a heat gun until it shrinks tight on the connector and sealant bubbles out the end.

How To Splice Underground Wire Seal The ConnectionTMB STUDIO

Step 5

Gel-Filled Splice Kit Repair

Start by cutting out the damaged sections. Then cut, separate and strip the ends of the buried cable. Do the same for the additional section of cable (if needed). Next, secure the wires in the brass holder. Locate the splice block in the protective shield. Wrap the shield around the splice and secure it. Then repower the circuit to make sure the splice works.

To make it easier to locate the splice in the future, mark it with bright-colored surveyor’s tape. Then refill the hole.

Step 6

Twist and pull to separate

Grab each of the side conductors with pliers. Then twist your hands in opposite directions to start the tear. Pull the conductors 180 degrees away from each other to separate and expose a length of 1-1/2 in. Strip 3/4 in. of insulation off the black and white wires.

How To Splice Underground Wire Twist And Pull To SeparateTMB STUDIO

Step 7

Match the colors and splice

Slide the black wires into opposite ends of the brass barrel and tighten the screws. Then do the same for the white and bare copper wires.

How To Splice Underground Wire Match The Colors And SpliceTMB STUDIO

Step 8

Position the splice on the shield

Place the splice block dead-center over the gel-filled shield. Clean off any debris that may have fallen into the gel. Then press the splice into the gel.

How To Splice Underground Wire Position The Splice On The ShieldTMB STUDIO

Step 9

Roll and snap

Roll the shield around the splice and align the plastic latches. Snap the latches, starting at the center and working toward the edges. Then install the zip ties and tighten with pliers.

How To Splice Underground Wire Roll And SnapTMB STUDIO

Step 10

Mark the location

Tie bright-colored surveyor’s tape around the splice and fill the hole with soil. Replace the grass and trim the tape at soil level so you can find it again.

How To Splice Underground Wire Mark The LocationTMB STUDIO

Step 11

Splicing Low-Voltage Cable

Besides underground power cable, it’s also possible to slice through low-voltage lighting, irrigation and telephone cable and coaxial cable. Since they’re low voltage, you may be tempted to just twist the wires and wrap the splice with electrical tape. It won’t work.

Instead, head to a home center and get a couple of low-voltage connectors for direct burial. They rely on gel to encapsulate the splice to prevent water intrusion and corrosion.

For low-voltage stranded cable, like you might find on lighting, use the wire nut/gel-filled tube style. Twist on the wire nut, plunge the connector into the tube until the gel oozes out the top, then snap the lid. For solid irrigation and telephone wire, shove the wires in an insulation piercing gel-filled connector and snap it closed.

How To Splice Underground Wire Splicing Low Voltage Cable CalloutsTMB STUDIO