Motor circuit calculator

Pick the motor. You get the wire, the overload setting, the largest breaker or fuse allowed, and the disconnect size.

The motor

Three-phaseSingle-phase

System voltage

Horsepower

Nameplate FLA (optional)

Service factor 1.15+ or temperature rise 40°C or less

Protection

Short-circuit protection

The wire

CopperAluminum

Wire type

Terminal rating

Hot location or bundled wires?

Hottest air temperature (°F)

Current-carrying wires together

How this is calculated

Conductors, short-circuit protection and disconnects are sized from the full-load current in Table 430.248 (single-phase) or 430.250 (three-phase), not the nameplate (430.6(A)(1)). Overloads use the nameplate (430.6(A)(2)).
Branch-circuit conductors: 125% of full-load current (430.22), checked against your terminal rating and any derating.
Maximum short-circuit protection from Table 430.52. If that isn't a standard size, the next larger size is allowed (430.52(C)(1) Ex. 1). Ex. 2 allows more if the motor won't start; that isn't calculated here.
Disconnect: at least 115% of full-load current (430.110(A)), and horsepower-rated at the motor voltage.
For one motor only. Feeders for several motors (430.24), Design B energy-efficient motors, wound-rotor, DC and hermetic A/C compressors (Article 440) aren't covered yet.