How much must the nonmetallic sheath extend inside the box and beyond any cable clamp?

The requirement for the nonmetallic sheath to extend inside the box and beyond any cable clamp is specified in the National Electrical Code (NEC). An extension of at least 1/4 inch is essential to ensure proper insulation and protection of the conductors. This small extension mitigates the risk of exposed conductors while also allowing for sufficient space for the cable clamp to securely hold the nonmetallic sheath in place, preventing the strain from being directly on the conductors.

Looking at the options, while a sheath extending 1/8 inch may seem sufficient, it does not provide the necessary assurance against exposure. The other measurements, such as 1/2 inch and 3/4 inch, exceed the requirement, but in practice, the code specifically mandates that a minimum of 1/4 inch is both adequate and compliant with safety standards. Therefore, the extension of the nonmetallic sheath must be at least this amount to ensure that cables are properly secured and safe within electrical boxes.