9

When installing an electrical box, am I supposed to pull part of whole Romex cable inside the box or I can remove the white insulation outside the box and insert only 3 wires (hot, neutral and ground) inside the box?

Look at the picture. I have pulled part of the Romex cable inside the box, but those clamps are too tight. I am not sure if I was supposed to pull it this way or not.

One of the cables is 14/3 and other 14/2.

electrical box

20

You need at least 1/4" of cable jacket inside the box

You need to make sure at least 1/4" of cable jacket enters the box. This is required by NEC 314.17(B) for metal boxes and (C) for plastic ones in order to ensure that the cable clamp clamps the jacket, strain-relieving the jacket to the box so that stresses on the cable aren't transmitted to the connections in the box and protecting the insulation on the wires inside the cable from being damaged by the clamp bearing directly on them:

(B) Metal Boxes and Conduit Bodies. Where metal boxes or conduit bodies are installed with messenger-supported wiring, open wiring on insulators, or concealed knob-and-tube wiring, conductors shall enter through insulating bushings or, in dry locations, through flexible tubing extending from the last insulating support to not less than 6 mm (¼ in.) inside the box and beyond any cable clamps. Where nonmetallic-sheathed cable or multiconductor Type UF cable is used, the sheath shall extend not less than 6 mm (¼ in.) inside the box and beyond any cable clamp. Except as provided in 300.15(C), the wiring shall be firmly secured to the box or conduit body. Where raceway or cable is installed with metal boxes or conduit bodies, the raceway or cable shall be secured to such boxes and conduit bodies.

(C) Nonmetallic Boxes and Conduit Bodies. Nonmetallic boxes and conduit bodies shall be suitable for the lowest temperature-rated conductor entering the box. Where nonmetallic boxes and conduit bodies are used with messenger-supported wiring, open wiring on insulators, or concealed knob-and-tube wiring, the conductors shall enter the box through individual holes. Where flexible tubing is used to enclose the conductors, the tubing shall extend from the last insulating support to not less than 6 mm (¼ in.) inside the box and beyond any cable clamp. Where nonmetallic-sheathed cable or multiconductor Type UF cable is used, the sheath shall extend not less than 6 mm (¼ in.) inside the box and beyond any cable clamp. In all instances, all permitted wiring methods shall be secured to the boxes.

Exception: Where nonmetallic-sheathed cable or multiconductor Type UF cable is used with single gang boxes not larger than a nominal size 57 mm × 100 mm (2¼ in. × 4 in.) mounted in walls or ceilings, and where the cable is fastened within 200 mm (8 in.) of the box measured along the sheath and where the sheath extends through a cable knockout not less than 6 mm (¼ in.), securing the cable to the box shall not be required. Multiple cable entries shall be permitted in a single cable knockout opening.

4
  • 1
    In Canada CEC also stipulates that, in addition to no-less than 1/4", also no more than 1/2" of sheath should be in the box. Not sure if NEC has anything to say about that. – J... Dec 7 '20 at 19:48
  • @J... -- I have not seen the NEC set a maximum on the amount of cable jacket inside a box, excessive jacketing could be written up for not being "neat and workmanlike" though (I'd have to look in the NECA-NEIS for NM cable installs) – ThreePhaseEel Dec 7 '20 at 21:25
  • Yes, it's a workmanship thing here too, but code is explicit about it, iirc. – J... Dec 7 '20 at 22:28
  • @J... -- interestingly, the NECA-NEIS don't cover it either (there's no NECA-NEIS for nonmetallic-sheathed cables, and NECA 1 is silent on the topic best I can tell) – ThreePhaseEel Dec 8 '20 at 0:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.