314.17(B) Metal Boxes and Conduit Bodies.

At least ¼ inch of cable sheathing must extend into the enclosure beyond any cable clamp.
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At least ¼ inch of cable sheathing must extend into the enclosure beyond any cable clamp.

Code Change Summary: Requirements were added for nonmetallic-sheathed cable and multiconductor Type UF cable entering metal enclosures.

For many years, when installing nonmetallic-sheathed cables, it has been standard industry practice to make sure at least ¼ inch of cable sheathing enters the box before stripping off the jacket to make terminations. This has always been a requirement for nonmetallic-sheathed cables entering plastic boxes but until now, there has never been similar code language for nonmetallic-sheathed cables entering metal boxes or conduit bodies.

In the 2017 NEC® proper changes were made to correct the issue. Now, whether terminating in a plastic or metal box, the jacket of nonmetallic-sheathed cables and Type UF cables must extend at least 1∕4 inch inside the box and beyond the cable clamp.

Below is a preview of Article 314. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC® edition of NFPA 70.

2014 Code Language:

314.17(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 (1∕4 in.) inside the box and beyond any cable clamps. 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.

2017 Code Language:

314.17(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 (1∕4 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 (1∕4 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.

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314.17(B) Metal Boxes and Conduit Bodies.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Which of the following is required when installing nonmetallic-sheathed cables?

A: The sheath must extend not less than 1∕2 inch inside the box.
B: The sheath shall extend not less than 1∕4 inch inside the box and beyond any cable clamp.
C: The sheath must extend not less than 1 inch inside a metal box.
D: The cable sheath shall be stripped off immediately upon entering a metal enclosure.
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