For cable assemblies with nonmetallic sheaths, how far must the sheath extend inside the box beyond any cable clamp?

The correct answer is that the sheath of a nonmetallic cable assembly must extend at least 1/4 inch inside the box beyond any cable clamp. This requirement is specified in the National Electrical Code to ensure that there is a sufficient amount of insulation exposed within the box to prevent any possible mechanical damage to the conductors from the clamp or edges of the box.

The requirement serves to maintain the integrity of the electrical connection and provide adequate protection against shorts and other potential hazards. By ensuring that there is a minimum length of sheath extending beyond the clamp, the installation adheres to safety standards and reduces the risk of insulation wear or damage that could result from the clamp pressing against the cable.

Other measurements, such as 1/2 inch, 1 inch, or 3/8 inch, exceed the specified minimum and are not required by the NEC for this particular scenario. The standard mandates specifically the 1/4 inch to balance effective protection with practical installation considerations, making it the appropriate choice for compliance.