When wiring luminaires, which part of the lamp holder must be connected to the same luminaire or circuit conductor?

The correct choice is the screw shell, as this part of the lamp holder is specifically designed to be connected to the circuit conductor. In lighting fixtures, the screw shell is where the lamp itself is installed, and it provides the necessary electrical contact for the lamp to operate. According to the National Electrical Code requirements, ensuring a proper connection at the screw shell maintains safe operation and helps to prevent issues such as arcing or overheating, which could lead to failures or hazards.

Other parts of the lamp holder, such as the base, connector, and shade, do not serve the purpose of providing a direct electrical connection to the circuit. The base is typically non-conductive and serves to physically support the lamp, while connectors may be involved in securing the lamp but do not directly engage with the circuit. The shade, meanwhile, is primarily for aesthetic or functional purposes regarding the emitted light and does not have any electrical function related to the circuit.