A portable ride-through (RT) tester provides a voltage drop at control circuitry of a motor starter to test its RT capabilities. The RT tester includes a variable transformer for manually controlling the magnitude of the voltage drop. Timing circuitry is programmed to count cycles of a 120 VAC input voltage to affect the occurrence and duration of the voltage drop. The primary windings of the transformer are connected to the 120 VAC. The variable secondary winding is connected to output terminals, which are electrically connected to the starter control circuitry via conductive probes. The power circuit of the starter is disengaged during testing. The timers sequentially provide the 120 VAC input voltage and the voltage drop at the starter control circuitry. Repeated testing at different durations and monitoring for tripping of relays/solenoids of the starter enables the tester to determine the exact ride-through capability of the motor starter.