Motor Circuit Protection Chart

The maximum branch-circuit short-circuit and ground-fault device ratings for motor circuits — NEC Table 430.52(C)(1) in full, as a percentage of the table full-load current, with the Exception 2 ceilings for hard-starting loads and the 430.32 overload percentages that do the actual running protection. Values are unchanged across the 2017, 2020, and 2023 editions (the 2023 edition renamed the table and added Design B premium-efficiency wording). The adopted edition in your jurisdiction governs.

Maximum OCPD rating, % of full-load current

NEC 430.52(C)(1)
Maximum rating of the branch-circuit short-circuit and ground-fault protective device, as a percentage of the 430.248/430.250 table full-load current. Round UP to the next standard 240.6 size when the percentage lands between ratings (Exception 1). The nontime-delay column also governs time-delay Class CC fuses.
Motor typeNontime-delay
fuse		Dual-element
(time-delay) fuse		Instantaneous-trip
breaker		Inverse-time
breaker
Single-phase300%175%800%250%
AC polyphase (squirrel-cage), non-Design B300%175%800%250%
Design B energy-efficient300%175%1100%250%
Synchronous300%175%800%250%
Wound-rotor150%150%800%150%
DC (constant voltage)150%150%250%150%
Instantaneous-trip breakers are permitted only as part of a listed combination controller (430.52(C)(3)); where the table setting won't hold starting current they may rise to 1300% — 1700% for Design B energy-efficient — with settings above 1100% requiring an engineering evaluation. Synchronous motors driving low-torque loads (power-factor correction duty) need no device above 200%.

Exception 2 — ceilings for hard-starting loads

430.52(C)(1) Ex. 2
Where the Exception-1 size still won’t carry the starting current, the device may grow to these absolute maxima — and no further.
DeviceCeiling
Nontime-delay fuse ≤ 600 A (incl. time-delay Class CC)400%
Dual-element (time-delay) fuse225%
Inverse-time breaker, motor FLC ≤ 100 A400%
Inverse-time breaker, motor FLC > 100 A300%
Fuse rated 601–6000 A300%

Overload protection, % of NAMEPLATE current

NEC 430.32
Separate overload device sizing for continuous-duty motors over 1 HP. Unlike everything else in Article 430, overloads size from the nameplate, not the tables. The maximum column applies only when the initial size can’t start the motor or carry the load.
Motor markingSize atAbsolute max
Service factor 1.15 or greater125%140%
Temperature rise 40°C or less125%140%
All other motors115%130%
The two 125% rows are independent — either marking qualifies. Solid-state overloads and starter heater tables implement the same percentages; set electronic overloads to the nameplate FLA and let the class curve do the rest.

The two-device system, in one paragraph

A motor branch circuit deliberately splits protection: the fuse or breaker from the first table clears short circuits and ground faults but is far too big to protect the conductors from overload — that job belongs to the overload relay from the third table, riding on the nameplate current. The conductors in between are sized at 125% of table FLC (430.22). Work the whole stack — FLA from the motor FLA chart, percentages from this page, wire from the ampacity chart — or read the finished math per motor on the motor circuit data chart.

Common questions

What size breaker do I need for a motor?

Start at 250% of the table full-load current for an inverse-time breaker on a squirrel-cage motor, then round UP to the next standard size when the math lands between ratings (Exception 1). A 25 HP, 460 V motor: 34 A × 250% = 85 A → 90 A breaker. Remember these are MAXIMUMS to let the motor start — the conductors are protected by the overload device, not this breaker.

Why can a motor breaker be so much bigger than the wire ampacity?

Motor circuits split protection into two jobs. The branch-circuit device (fuse or breaker, this chart) only guards against short circuits and ground faults, so it is sized big enough to ride through the six-times-FLA starting inrush. Overload protection — the thing that keeps 8 AWG safe on a 40 A motor — is the separate overload relay in the starter, sized at 115–125% of nameplate current per 430.32.

What is the difference between the 175% and 300% fuse columns?

Fuse speed. A dual-element time-delay fuse holds five times its rating for ten seconds, so it can be sized at only 175% of FLC and still let the motor start — closer protection, smaller switch. A nontime-delay fuse would blow on inrush at that size, so the code allows 300%. It is why dual-element fuses are the default in motor circuits (and why time-delay Class CC fuses, oddly, use the 300% column — they behave like fast fuses at inrush multiples).

What if the motor still won’t start at the table percentage?

Exception 2 sets absolute ceilings: 225% for a dual-element fuse, 400% for a nontime-delay fuse up to 600 A, 400% for an inverse-time breaker on motors up to 100 A FLC (300% above that), and 300% for fuses 601–6000 A. Past those numbers the fix is a different device or a reduced-voltage start, not a bigger fuse.

Is overload sizing based on nameplate or table current?

Nameplate — the one place Article 430 uses it. Overloads: 125% of nameplate FLA for motors marked service factor 1.15+ or temperature rise 40°C or less, 115% for everything else (430.32). If that size cannot start the motor, the next size up is allowed to a hard cap of 140%/130%. Everything else — conductors, fuses, breakers, disconnects — sizes from the 430.248/430.250 table values instead.

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