This project explains how to repair a damaged electrical wire by splicing in a new section of NM-B 14/2 wire with junction boxes.

The 120VAC wire splice fix is illustrated in the following diagram:

NM 14-2 Electrical Wire Repair Splice Diagram

This splice repair technique is useful for fixing damage when there’s not enough slack in the electrical cable to rejoin the ends together with wire nuts in a single junction box. For example, if a squirrel or rodent has a chewed through an electrical cable in the attic, or in my case, I also had to reroute the wire to correct a building code violation.

How to Repair a Damaged Electrical Wire

Damaged Electrical Wire and Building Code Violation

This run of 120VAC Romex NM 14/2 (Non-Metallic 14 gauge, 2 conductor with ground wire) electrical cable in the finished basement has several problems:

  1. National Electrical Code (NEC) violation because it’s hanging unsupported outside the 2×4 studs. An example of sloppy work by the former homeowner.
  2. The insulation has been cut on both the outer sheath and inner hot wire conductor then wrapped with electrical tape which is a improper repair method.
Damaged NM-B 14/2 Electrical Wire and Building Code Violation

Damaged NM-B 14/2 Electrical Wire and Building Code Violation

Close-up of the damaged insulation. My guess is the the goober who installed the cable planned to cut it but changed his mind. It doesn’t explain why the hot wire (black) insulation is exposed. If you’re going to cut a wire, you don’t need to hack away at the insulation.

NM 14/2 Wire - Damaged Insulation

NM 14/2 Wire – Damaged Insulation

NM 14/2 Wire Splice Repair

The house electrical wire is repaired by:

  1. Cutting the cable in two at the damaged area.
  2. Rerouting the upper portion of the cable inside the crawlspace and 2×4 wall studs to correct the building code violation.
  3. Splicing in a new span of NM 14/2 wire with two junction boxes.

The result is shown in this photo:

Repaired NM 14/2 Wire with Junction Boxes and Splice

A keen eye will note the black cable crossing in front of the 2×4 studs at the top right corner in the above photo – that’s the cable TV coaxial cable. I wouldn’t have routed it that way, however it’s not a safety or code problem.

NM-B 14/2 Electrical Cable Repair Parts and Tools

Two flush mount 4″ square by 1.5″ deep electrical junction boxes are required to splice in the repair span of NM 14/2 electrical cable. There are two types of steel electrical boxes:

  • with built-in cable clamps (left box in photo below)
  • without cable clamps (right box in photo below)

4″ Steel Electrical Box with Cover and NM Cable Clamps

For this repair I only needed the box with built-in cable clamps, although I used both types because I happened to have a box without clamps left over from a prior job. If you buy a box without clamps or need to bring in wires from another direction, the 1/2″ NM Cable Connectors are necessary to secure the wire in the knockout hole.

The parts are inexpensive, the electrical box with internal clamps cost $1.19 and a box cover is only 57 cents.

The steel junction boxes must be grounded but do not include the ground screw, so I bought a 10-pack of #10-32 green ground screws for $1.31. The #10-32 ground screw fits the smaller hole near the center of the steel electrical box.

Halex 10-32 Green Ground Screw

Halex 10-32 Green Ground Screw

Closeup of the how the 14/2 NM electrical wire and NM Cable Connector are installed in the steel junction box. To install the cable, remove the 1/2″ inner knockout, attach the cable connector and lock nut, insert the wire and tighten the clamp screws until the cable is snug.

4" Electrical Junction Box with 1/2" NM Cable Connector

4″ Electrical Junction Box with 1/2″ NM Cable Connector

Knockouts are the several dimpled circles in the box sides. To remove a knockout, just hit it near the inner edge with the tip of a screw driver then bend it back and forth until the disc tab breaks.

A box of Romex NM 14/2 electrical wire, wire nuts and cable staples are needed. You can buy Romex in 25, 50 and 100 foot length boxes and coils at the home improvement store. Copper wire is getting expensive to rising metal prices, so only buy the minimum length of wire needed for your repair.

Romex NM 14/2 Wire, Wire Nuts and Cable Staples

Romex NM 14/2 Wire, Wire Nuts and Cable Staples

I used the following tools in this electrical wire repair job:

  1. Cordless drill/driver to attach the junction boxes to the 2×4 studs with wood screws
  2. Diagonal cutting pliers
  3. Needle nose pliers with cutter (you can get by with this only if you don’t have #2)
  4. Hammer for the cable staples
  5. Philips screw driver
  6. Utility knife
  7. Multi Tool wire stripper and cutter (does a better job stripping wires than the utility knife)
  8. Receptacle tester
  9. Non-contact voltage detector
  10. AC Voltage Tester (if you have #9 then you don’t need this tool)

House Electrical Wire Repair Tools

This repair is continued in How to Repair a Damaged Electrical Wire – Part 2.

Take care,

Bob Jackson

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