Challenge #8 · motors
Trips Every Time, And It's Not Electrical
A 480V motor trips its breaker the instant you start it. The operator's sure it's "an electrical problem." (Lock it out before you put hands on anything.)
① Run your checks
② Make the call
③ Explain your reasoning optional
A strong answer covers:
- What you did: ruled out the electrical side (all three legs at 480, balanced windings), then (locked out) tried to turn the shaft by hand.
- The reason: power and windings are healthy, but the shaft won't turn, so the rotor is mechanically locked.
- Determined outcome: a locked rotor (seized bearing or jammed load) holds the motor at locked-rotor current and trips the breaker, which is protecting it; the fix is mechanical, the motor and breaker are fine.