When connecting 100' of No. 16 fixture wire to a standard 120V circuit, what is the maximum branch-circuit overcurrent protection device allowed?

The maximum branch-circuit overcurrent protection device allowed when using No. 16 fixture wire is 20A. This is because No. 16 wire is typically rated for a maximum current carrying capacity of 10A in most applications, according to the National Electrical Code (NEC) guidelines. However, to protect the wiring effectively without risking overheating, the overcurrent protection device should be rated higher than the wire’s capacity but not exceeding it to ensure safety.

The 20A overcurrent protection serves to effectively guard the wire from potential overload while allowing sufficient current flow for standard electrical fixtures. It's essential to select a protection device that avoids excessive trip conditions, allowing the circuit to operate correctly without jeopardizing the integrity of the wiring.

Wiring larger than what is suitable for the circuit (like a 30A or 40A device) not only poses a safety risk but also can lead to overheating of the wire, increasing the potential for fire hazards. Thus, 20A is the maximum allowable overcurrent protection for a standard setup with No. 16 fixture wire in a typical 120V circuit.