Can I use a circuit breaker for motor overload protection?

Usually not. Article 430 treats motor overload protection and motor branch circuit short circuit and ground fault protection as two separate functions with two separate sizing rules. A breaker sized to let the motor start is far too large to protect the windings from a sustained overload. There are specific cases in 430.32 where the branch circuit device is permitted to do both, but they are narrow.

Why one device rarely covers both

Table 430.52(C)(1) permits an inverse time breaker for a squirrel cage motor to be sized up to 250 percent of full load current, and the exceptions allow going higher when the motor will not start. That size exists to ride through locked rotor inrush, which can be six to eight times full load current for several seconds.

Overload protection under 430.32(A)(1) is a completely different number. For a continuous duty motor rated more than 1 horsepower, the separate overload device is sized at 125 percent of the motor nameplate full load current when the service factor is 1.15 or greater or the temperature rise is 40 degrees C or less, and 115 percent otherwise. A motor drawing 28 amps gets an overload element around 35 amps and a branch circuit breaker as large as 70 amps. A 40 amp overload condition would cook the motor for a long time before a 70 amp breaker noticed.

When the breaker is allowed to serve as the overload device

Section 430.32(B) covers motors of 1 horsepower or less that are not permanently installed, are manually started and are within sight from the controller. In that case the branch circuit short circuit and ground fault protective device is permitted to serve as the overload device, provided it does not exceed the values in 430.52. Section 430.32(D) extends similar treatment to certain permanently installed motors of 1 horsepower or less where the device rating does not exceed the overload values calculated from 430.32(B)(1).

Section 430.32(A)(2) also allows a thermal protector integral to the motor to serve as overload protection, which is what covers most small fractional horsepower motors, and 430.32(A)(3) covers motors with an impedance limited winding.

What to install instead

The standard arrangement is a breaker or fuse sized per 430.52 for short circuit and ground fault, plus a motor starter with thermal overload elements or an electronic overload relay sized per 430.32. A listed manual motor protector or a motor circuit protector combination starter packages both functions in one enclosure and is the cleanest solution when panel space is tight. Section 430.32(C) permits bumping the overload setting to 140 percent when the motor will not start or run at the calculated value, which is the legal path when a motor trips on startup.

Field takeaway

Size the breaker for starting current under 430.52 and the overload separately under 430.32. Only motors 1 horsepower or less that meet the 430.32(B) or 430.32(D) conditions, or motors with integral thermal protection, get by on the branch circuit device alone.