Motor Wire Size Guide: Inputs to Verify

Horsepower or one current value alone cannot determine a motor conductor safely.

What affects selection?

  • Motor type and the current source required by the applicable rule; nameplate, table, and estimated currents are not interchangeable.
  • Voltage, phase, circuit arrangement, conductor material, insulation and terminal ratings, and equipment listing.
  • Ambient temperature, conductor count, wiring method, grouping, and conditions affecting allowable ampacity.
  • Circuit length and operating conditions for a separate voltage-drop review; it does not replace ampacity or protection checks.
  • Overload, short-circuit and ground-fault protection, disconnecting means, and motor-specific rules.

Verification steps

  1. Read the motor nameplate and equipment instructions; identify location and adopted code edition.
  2. Determine which current source each rule requires and verify conductor ampacity against the official source and installation conditions.
  3. Check voltage drop, protection, terminals, listing, and coordination separately. Have a qualified professional review the design before installation.

This page gives no universal wire chart or wiring prescription. For U.S. installations where adopted, check the locally adopted edition of NFPA 70.