where voltage drop affects a motor circuit, which of the following should be used to size the conductors?

The conductors must be sized using the full-load current of the motor from the NEC/CEC ampacity tables, adjusted for voltage drop , not just the overcurrent protective device rating.

Direct answer

Where voltage drop affects a motor circuit, use the motor’s calculated or nameplate full-load current and the appropriate conductor ampacity table (e.g., NEC Table 430.250 / 310 ampacity tables) as the basis for sizing the conductors, then increase the conductor size as needed so the voltage drop stays within acceptable limits (commonly 3% for a branch circuit and 5% total for feeder plus branch).

Why this matters for motors

• Motors draw higher current when voltage drops, which increases heating and can damage windings and insulation.

• Voltage drop reduces available torque roughly with the square of voltage, so undersized conductors can prevent proper starting and cause stalling.

Practical exam-style framing

On many licensing/NEC-style exam questions, the correct choice is:

• Size the conductors from the motor full‑load current values in the code tables (not the breaker size),
• Then check and upsize as needed so calculated voltage drop does not exceed recommended limits (e.g., 3% branch, 5% total).

This aligns with typical voltage‑drop practice questions and technical notes on choosing larger conductors when long runs cause excessive drop.

Information gathered from public forums or data available on the internet and portrayed here.