When the main bonding jumper is a screw, which characteristic must it have according to the NEC®?

The correct answer is that when the main bonding jumper is a screw, it must have a listing mark visible when the screw is installed, as specified by the National Electrical Code (NEC®). This requirement is in place to ensure that the component used for bonding is compliant with safety standards and has been tested for its electrical properties.

A listing mark signifies that the product has been evaluated by a recognized testing laboratory and meets specific safety and performance standards. This is important in ensuring that the electrical system is safe and reliable, minimizing the risks of faults or failures. Having a listing mark visible after installation allows for easier verification of compliance during inspections and maintenance checks, ensuring that installers and inspectors can readily confirm the legitimacy of the component in use.

While the other characteristics such as a green finish or hexagonal head can be important in different contexts, the NEC® specifically emphasizes the necessity of being able to verify the legitimacy and safety through the visibility of the listing mark once installed. This focus on compliance through recognizable testing marks is crucial for maintaining standards in electrical installations.