Enter readings below — each check verdicts itself as you go
Work safe. Isolate and lock off before touching terminals. Discharge capacitors (across a resistor) and test them out of circuit.
Capacitorskip if not testing one
Amps vs nameplateclamp meter, running
3-phase voltage balance3-phase only
3-phase current balance3-phase only
How these checks work
Capacitor: capacitors must measure within the tolerance printed on their label — commonly ±5–6% for run caps and ±10–25% for start caps. Weak caps cause hard starts and high running amps; near-zero µF is a dead cap.
Amps: running current is compared to nameplate RLA. Well over = overloaded (voltage, head pressure, bearings). Well under = lightly loaded (low charge, not pumping). If running amps sit near locked-rotor amps, the motor isn't turning at all.
Voltage imbalance (NEMA method: max deviation from the average of the three line-to-line voltages) should be under 2%. Current imbalance runs 6–10× voltage imbalance, which is why a small supply problem cooks windings. Over 5% — don't run it.
Current imbalance over ~10% points at windings, connections or supply; severe imbalance usually means a lost phase.
Diagnostic guide only — compare to the nameplate and your own judgement.