Motor Full-Load Current Calculator

Table FLC vs. nameplate current

A motor's nameplate lists a full-load amps (FLA) value measured for that specific machine. The NEC deliberately does not use it for general circuit sizing. NEC 430.6(A)(1) directs that conductor ampacity, branch-circuit short-circuit and ground-fault protection, and the disconnecting means all be sized from the tabulated full-load current in Tables 430.247 through 430.250, selected by horsepower and voltage. The tables give a single, conservative, code-consistent value so two electricians sizing the same 10 hp, 460 V circuit always land on the same 14 A basis.

The nameplate current has exactly one job in the NEC scheme: the running overload protection (NEC 430.6(A)(2) and 430.32), which protects the motor itself and is sized on the actual nameplate FLA. That is a separate calculation handled by the Motor Overload Protection Calculator.

Sizing the conductor: NEC 430.22

Once you have the table FLC, the branch-circuit conductors of a single continuous-duty motor must carry at least 125 percent of it:

minimum conductor ampacity = table FLC x 125%

This is a required ampacity in amperes, not a wire gauge. You still select the actual conductor from Table 310.16 at the equipment's termination temperature (typically the 75 degree C column) and apply any ambient-temperature or more-than-three-conductor derating. The Wire Gauge and Wire Ampacity calculators do that step.

Worked examples

Three-phase, 460 V. A 10 hp, 460 V three-phase motor: Table 430.250 lists 14 A.

FLC = 14 A; conductor min = 14 A x 125% = 17.5 A

Single-phase, 115 V. A 1 hp, 115 V single-phase motor: Table 430.248 lists 16 A.

FLC = 16 A; conductor min = 16 A x 125% = 20 A

Voltage matters. The same 10 hp three-phase motor is 28 A at 230 V but 14 A at 460 V, because current scales inversely with voltage for a given horsepower, which is why larger motor feeders are usually run at 460 V.

How this differs from the other motor tools

This page is the raw table lookup: the full-load current and the one conductor figure that follows straight from it. The tools that compute a device rating take it from here:

• Motor Breaker Sizing Calculator: branch-circuit short-circuit and ground-fault device per Table 430.52 (up to 250 or 300 percent of FLC) plus the conductor.
• Motor Overload Protection Calculator: the running overload, sized on the nameplate FLA (430.32), not the table FLC.
• Motor & HVAC Disconnect Sizing Calculator: the disconnect ampere rating (430.110), at least 115 percent of FLC.

Frequently asked questions

Where does motor full-load current come from?

From NEC Table 430.248 (single-phase) or Table 430.250 (three-phase) by horsepower and voltage. Per NEC 430.6(A)(1), this table value, not the motor nameplate current, sizes the branch circuit and feeder. A 10 hp, 460 V three-phase motor is 14 A.

Nameplate current or table FLC?

Table FLC for conductor ampacity (430.22), branch-circuit protection (430.52), and the disconnect (430.110). The nameplate FLA is used only for the running overload (430.32).

How do I size the conductor from FLC?

Take 125 percent of the table FLC (NEC 430.22) to get the required ampacity, then pick the conductor from Table 310.16 at the termination temperature with any derating. A 10 hp, 460 V motor needs 14 x 1.25 = 17.5 A of ampacity.

Which motor types are covered?

Single-phase AC motors (Table 430.248) and three-phase AC induction motors, squirrel-cage and wound-rotor (Table 430.250). Synchronous and DC motors have their own tables and are outside this lookup.

Related calculators

• Motor Breaker Sizing Calculator: branch-circuit breaker or fuse and conductor per NEC Table 430.52 and 430.22.
• Motor Overload Protection Calculator: the running overload relay per NEC 430.32, on the nameplate current.
• Motor & HVAC Disconnect Sizing Calculator: the minimum disconnect ampere rating per NEC 430.110 / 440.12.
• Wire Gauge Calculator: the minimum AWG for a required ampacity with full NEC derating.