How to Repair a Damaged Electrical Wire – Part 3

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How to Repair a Damaged Electrical Wire – junction box wiring to complete the wire splice repair. This project is continued from How to Repair a Damaged Electrical Wire – Part 2.

NM-B 14/2 Junction Box Splice Wiring

These next steps explain how to wire the junction box. Begin by cutting the two Romex NM 14/2 electrical cables evenly to about 8 inches long as shown:

Junction Box Wiring Splice Wiring: 6" inch Wire Leads

Junction Box Wiring Splice Wiring: 6″ inch Wire Leads

Strip at least 6 inches of insulation from the wire leads by cutting a 3/4″ long slit in the outer insulation sheath with the utility knife as shown, drawing the knife from the body of the wire towards the end. Per NEC 300.14, all conductors must extend at least 6 inches in the box and at least 3 inches beyond the box.

Junction Box Wiring: Remove the Outer Insulation Jacket

Junction Box Wiring: Remove the Outer Insulation Jacket

Pull to peel the outer insulation off like a banana from the NM 14/2 wires, then cut the insulation “peel” off at the base with the knife blade facing away from the inner wires so there’s no chance of nicking the insulation of the hot (black) and white (neutral) wires. The NM-B 14/2 outer jacket must extend at least 1/4 inch past the cable clamps into the junction box.

Junction Box Wiring: Peel off the NM-B 14/2 Outer Insulation

Junction Box Wiring: Peel off the NM-B 14/2 Outer Insulation

Using either the utility knife or the wire strippers, remove 3/4″ of insulation from the hot and neutral wires:

Junction Box Wiring: Strip 3/4" of Insulation from the Wires

Junction Box Wiring: Strip 3/4″ of Insulation from the Wires

Wire strippers work great, just fit the wire in the 14 gauge slot, close the jaws and pull. A perfect cut every time!

NM-B 14/2 Wire Strippers

NM-B 14/2 Wire Strippers

Use the needle nose pliers to twist the wire leads together, matching the hot (black), neutral (white) and ground (bare copper) wires. You should have about 5/8″ of exposed copper wire after twisting the leads together. If the twisted section is too long, snip off the end so it’s 5/8″ long such that the copper conductors are completely covered by the wire nut. The junction box is grounded by installing a #10-32 green ground screw to attach a bare copper wire pigtail that is wire nutted to the other ground wires.

Secure the wires by twisting on a wire nut until tight.

Junction Box Splice Wiring: Wire Nut Connections

Junction Box Splice Wiring: Wire Nut Connections

Fold the wires into the junction box as shown, using gentle bends to avoid stressing the wires.

The junction box cover plate attaches with two screws that are provided with the box. Note the cover plate has “Under Side” stamped on the lid to indicate the side that faces the box.

Junction Box Cover Plate

Junction Box Cover Plate

Slide the cover plate on the junction box and tighten the two screws. Cover plates are required by the National Electrical Code.

Fasten the Junction Box Cover Plate with Screws

Fasten the Junction Box Cover Plate with Screws

Electrical Wire Repair Splice

Here’s a photo of the completed wire repair splice and new junction boxes:

Romex NM 14/2 House Electrical Wire Repair Splice

After the junction box wiring is complete turn on the circuit breaker to restore the electricity. Use the non-contact voltage detector to verify the wires are powered. Check that the lights and/or electrical outlets are functioning. If outlets are powered by the circuit, verify the outlets are working and wired correctly with the receptacle tester.

Take care,
Bob Jackson

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10 Comments

  1. Peter Coleman March 11, 2014 at 3:07 am - Reply

    Good article, but there’s no need to attach a separate ground wire. Loop the ground wire from one of the cables around the ground screw, then twist them together and attach wire nuts.

  2. Garry Hall June 16, 2015 at 9:43 pm - Reply

    If there is plenty of slack in the damaged wire, can I just make this repair with one box?

    Great article, thank you!

    • Bob Jackson June 17, 2015 at 8:35 am - Reply

      Yes – a single junction box is all you need for the repair splice if there’s sufficient slack in the wire.

  3. Rob H May 28, 2016 at 7:17 pm - Reply

    It appears that these junction boxes will eventually wind up behind some drywall. Don’t they need to be kept accessible per code?

    • Bob Jackson May 29, 2016 at 9:49 am - Reply

      I covered that point in Part 2 of the project:

      Note: Junction boxes must not be concealed; if drywall is ever installed then an access panel is required to reach the junction box.

  4. Ken April 2, 2017 at 10:25 am - Reply

    Can I put an outlet at a junction box?

  5. Joseph Leslie Busch April 30, 2017 at 2:28 pm - Reply

    I had to make this repair where a rat had chewed all the insulation of the wires for 1.5 inches after i cut out the bad wire the wires were too short to hook together so i used 2 junction boxes with cable clamps and added 10 inches of the same size wire the wires i was repairing did not have ground wires i thought that was odd but it is from a trailer house built in 1978 so i did not hook up any ground wires inside the junction boxes the new wire that i tied the 2 older pieces of together with had a ground wire but i figured because the older wire had no ground i did not need to hook up a ground wire to the junction boxes i was wondering if this is correct thank you for letting me know if this is correct

    • Bob Jackson May 1, 2017 at 7:15 pm - Reply

      The National Electrical Code (NEC) has required ground conductors since the 1960’s (.pdf pages 4, 5 and 12, 13). Was the damaged electric cable Romex or some other brand?

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