How to Use This Chart

Use table FLA for conductor (125%), disconnect (115%), and max OCPD (Table 430.52). Use nameplate FLA for overload settings. Calculator: motor circuit sizing calculator. Guide: motor circuit sizing guide.

Where NEC Table 430.250 FLA Values Come From

Article 430 does not want you to size the branch circuit from the motor nameplate current. Nameplates vary by manufacturer, efficiency, and design letter; two 10 hp, 460 V motors can differ by an amp or more. The Code instead publishes standardized full-load currents in Tables 430.247 (DC), 430.248 (single-phase AC), 430.249 (two-phase), and 430.250 (three-phase AC). Those figures are conservative planning currents — historically a bit higher than typical nameplates — so that conductors and disconnects sized from the table will work across common motor lines without a special calculation for every catalog.

This chart’s FLA columns are the Table 430.250 three-phase induction values as used in the TestTalkHQ motor calculator, at 230 V and 460 V. Other voltages (208, 575, etc.) have their own columns in the NEC table; do not scale 460 V FLA by a voltage ratio and call it 208 V unless you are looking at the actual table row. Design B, C, and D induction motors share this table; some other motor types do not. If the nameplate FLA is higher than the table, you still use the table for conductors and OCPD in the usual 430.6(A) method, and you use the nameplate for overloads. If you only have horsepower and voltage, the table is the starting point; if you are setting a heater, grab the nameplate.

Why the 125% Continuous-Load Factor Exists

Motors are treated as continuous loads. NEC 430.22 requires branch-circuit conductors supplying a single motor to have an ampacity of at least 125% of the Table 430.250 (or applicable table) FLA. The extra quarter is thermal margin for a load that can run indefinitely, plus the reality that motors draw more than FLA during start and can run warm at service factor. It is the same 125% idea you see on other continuous loads in Article 210, specialized here so motor circuits are consistent.

The “Cond. 125%” columns on this chart are that minimum ampacity target, not a wire gauge. You then pick a conductor whose ampacity (after temperature, bundling, and termination limits) is at least that number, and you still have to land on a termination rated for the conductor. A 10 hp at 460 V shows 14 A FLA and 17.5 A at 125% — that is often 12 AWG copper in a friendly installation and not 14 AWG just because 15 A “looks close.” The chart stops at the ampacity number; 310.16 / 310.15 and the conditions of use finish the job.

Three Numbers People Conflate

1. Branch-circuit conductor sizing — 125% of table FLA (430.22), then apply ampacity derates. This is the wire. It is not the breaker size and it is not the overload heater.

2. Short-circuit and ground-fault protection — the branch-circuit device that clears a fault (breaker or fuse), sized from Table 430.52 as a maximum percentage of table FLA. Inverse-time breakers go to 250% in the standard column; dual-element fuses 175%; non-time-delay fuses 300%; instantaneous-trip MCPs much higher, with extra rules. You select the next standard size that does not exceed that maximum (with the 430.52 exceptions when the motor will not start). A 10 hp 460 V motor at 250% is 35 A — that is a planning ceiling, not a requirement to use a 35 A breaker if a 30 A starts the motor. This device is allowed to be larger than the conductor ampacity because 430.52 is protecting against short circuits, and the overload device protects the motor and, in combination, the conductors against overload.

3. Overload relay (heater / electronic overload) sizing — set from nameplate FLA, typically 115% or 125% depending on service factor and temperature rise (430.32). This is the only one of the three that should track the metal plate on the motor. Putting the overload at 250% of table FLA because “that is what the chart says for the breaker” is how motors burn up with a legally sized breaker still sitting there closed.

Work a 20 hp, 460 V example without copying every cell: table FLA 27 A; conductor target 33.8 A; inverse-time breaker maximum 68 A; overload from a nameplate that might read 25.4 A, not 27. Three answers. The motor circuit sizing calculator keeps them on separate lines on purpose. Non-motor breaker sizing is a different article: circuit breaker sizing chart.

What This Chart Will Not Do

It does not size VFDs, soft starters, or 430 Part X adjustable-speed drive conductors (those have their own 125%/150% rules). It does not replace a motor feeder calculation for several motors on one feeder (430.24). It does not pick dual-element fuse vs breaker for coordination. And the 230 V columns are not 208 V — use the NEC table or the calculator for 208 V FLA.

3φ Induction Motors — Table FLA & Planning Multipliers

FLA values from NEC Tables 430.248 / 430.250 (as used in the TestTalkHQ motor calculator). Select next standard conductor ampacity and next standard breaker ≤ maximum.

Table 430.52 — Max Branch OCPD (% of Table FLA)

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