The symptom pattern
The reported pattern is consistent across sources: the machine hums at mains frequency when switched on, the cutterblock either doesn’t turn or creeps slowly, and the breaker or the motor’s thermal cutout trips within seconds. A single-phase induction motor that hums but won’t start has failed to develop starting torque — the question is whether the start circuit (capacitor, centrifugal switch) or the windings themselves are at fault.
Working through the causes
In rough order of likelihood:
- Start capacitor — the most common failure on this class of machine and by far the cheapest to fix. Capacitors age poorly in unheated workshops; a bulged case, visible leakage, or a capacitance reading far below the printed rating condemns it. Replace like-for-like on capacitance and voltage rating.
- Centrifugal switch — stuck or burnt contacts stop the start winding from being energised (or from dropping out once the motor is up to speed). A healthy switch clicks audibly as the motor spins down after being switched off; silence is suspicious.
- Windings — the expensive one. Open, shorted, or earthed windings show up on resistance measurements at the motor terminals, and cooked windings usually announce themselves with a burnt-varnish smell. Any continuity between a winding and the motor frame is an earth fault: stop, and do not run the motor again until it’s repaired or replaced.
Before any electrical testing, rule out the mechanical explanation: with the machine unplugged, the cutterblock and belt should spin freely by hand. A seized bearing or jammed drive produces the same hum-and-trip symptom with a perfectly healthy motor.
Verdict
Test the capacitor first — statistically it’s the answer, and it costs little to rule out. If the windings are genuinely gone, get a rewind quote from a local motor shop and compare it against a replacement motor: on machines of this class the rewind is often uneconomical, but prices vary enough that it’s always worth the phone call.