How to Size a Motor Breaker: NEC Table 430.52 (2020 NEC)

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The rule

For a three-phase squirrel-cage motor, the inverse time breaker that protects the branch circuit from short circuits and ground faults can be up to 250% of the motor's full-load current (FLC) from the motor tables in the 2020 NEC (NFPA 70). If 250% is not a standard size, 430.52(C)(1) Exception No. 1 lets you go up to the next standard size in 240.6(A).

Motor breaker size calculator (Table 430.52)

Pick the motor type and protective device, then look up the full-load current by horsepower and voltage or type it in. The calculator applies the Table 430.52 percentage, rounds up to the next standard size and shows the start-up limit.

Step 1: Get FLC from the table, not the nameplate

For branch-circuit short-circuit and ground-fault protection, 430.6(A)(1) sends you to the motor tables instead of the nameplate: Table 430.248 for single-phase motors and Table 430.250 for three-phase motors. Look up the motor by horsepower and voltage.

The nameplate current is for separate overload protection, not this step (430.6(A)(2)). One catch: motors built for low speeds (less than 1200 RPM) or high torques, and multispeed motors, use the nameplate current (430.6(A)(1)).

Step 2: Multiply by the Table 430.52 percentage

Find your motor type in Table 430.52, then read the inverse time breaker column:

• Single-phase motors: 250%
• AC polyphase motors other than wound-rotor (squirrel cage, including Design B energy-efficient): 250%
• Synchronous: 250%. Low-torque, low-speed synchronous motors (usually 450 rpm or lower) that start unloaded don't need more than 200% (footnote 3).
• Wound-rotor: 150%
• DC (constant voltage): 150%

The same table has columns for nontime-delay fuses, dual-element (time-delay) fuses and instantaneous trip breakers. Use the column for the device you are installing. Whatever device you pick must be able to carry the motor's starting current (430.52(B)).

Step 3: Round up to the next standard size if needed

If your result is not a standard rating, 430.52(C)(1) Exception No. 1 lets you use the next higher standard size from 240.6(A). Standard sizes in this range: 60, 70, 80, 90, 100, 110, 125, 150, 175 and 200 A.

Worked example

A 25 hp, 460 V, three-phase squirrel-cage motor:

1. Table 430.250: FLC = 34 A.
2. 34 A × 250% = 85 A.
3. 85 A is not a standard size. The next standard size up is 90 A.

Answer: 90 A maximum inverse time breaker.

If the motor won't start

If the breaker from Step 3 can't handle the starting current, 430.52(C)(1) Exception No. 2(3) lets you go larger. An inverse time breaker can't exceed 400% of FLC for motors with FLC of 100 A or less, or 300% for FLC over 100 A. There is no rounding up past this limit.

In the example: 34 A × 400% = 136 A. The largest standard breaker that does not exceed 136 A is 125 A.

One more limit: if the manufacturer's overload relay table, or a marking on the equipment, shows a lower maximum, don't exceed it (430.52(C)(2)).

Same motor, with dual-element fuses

Table 430.52 gives dual-element (time-delay) fuses 175% instead of 250%. For the same 25 hp, 460 V motor: 34 A × 175% = 59.5 A. The next standard size up in 240.6(A) is 60 A.

If the motor won't start on those, Exception No. 2(2) lets time-delay fuses go up to 225% of FLC: 34 A × 225% = 76.5 A, so 70 A is the largest standard size that doesn't exceed it.

Same motor, different device, different answer. Always read the column for what you're installing.

Want more practice? Try JCR's free 25-question practice exam.

Common questions

What size breaker for a 25 hp, 460 V three-phase motor?

Up to a 90 A inverse time breaker for a squirrel-cage motor. Table 430.250 gives 34 A, × 250% = 85 A, and the next standard size is 90 A.

Do you round up when sizing a motor breaker?

Yes, once. If the Table 430.52 result isn't a standard size, you may go to the next higher standard rating (430.52(C)(1) Exception No. 1). Past that, only the starting-current limits in Exception No. 2 allow more.

Is the motor breaker sized from the nameplate?

For most motors, no. Use the full-load current from Table 430.248 or 430.250 (430.6(A)(1)). The nameplate is for overload sizing.

Is there a motor breaker sizing chart?

Table 430.52 is the chart. It sets a maximum percentage of the table full-load current for each motor type and protective device, such as 250% for an inverse time breaker on a squirrel-cage motor. The calculator above does the math and the round-up.

This answer uses the 2020 NEC. You can buy the 2020 NEC here or view it online with a paid NFPA LiNK subscription. Check which NEC edition your state tests on.

JCR checked this answer against the 2020 NEC in NFPA LiNK on October 21, 2026.

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