NEC Commercial Electrical Practice Test

Which conductor should be connected to the screw shell of screw shell type lamp holders supplied by a circuit with a grounded conductor?

1. Grounded (neutral/white) conductor

2. Hot conductor

3. Grounding conductor

4. Equipment grounding conductor

The correct answer is: Grounded (neutral/white) conductor

The screw shell of screw shell type lamp holders is designed to provide a safe and effective electrical connection while ensuring that the lamp holder is grounded properly. Connecting the grounded (neutral) conductor to the screw shell helps prevent the risk of electric shock. This is because, in the event of a fault where the hot conductor could become exposed, the grounded shell allows for a safe path for any potential fault current to flow, minimizing the hazard. In lighting applications, the grounded conductor, typically the neutral (white) wire, is meant to return current back to the service panel safely. This connection helps to ensure that if there is a malfunction and the hot conductor comes into contact with the shell, the circuit will facilitate a lower resistance path back to the grounding system, tripping the circuit breaker and de-energizing the circuit. This grounding principle enhances safety for users who may touch the lamp holder and protects connected devices from electrical faults. Therefore, connecting the grounded conductor to the screw shell of a lamp holder ensures compliance with safety standards set forth by the National Electrical Code (NEC).