Overload Relays

Overload relays are protective devices used in motor control circuits to detect and interrupt sustained overcurrent conditions that would otherwise cause motor winding damage or premature failure. Controls engineers, panel shops, and machine builders specify overload relays wherever motors must be protected against thermal overload, phase loss, or locked-rotor conditions. This category includes bimetallic thermal overload relays for traditional contactor-mounted or separately mounted IEC and NEMA applications, electronic overload relays offering adjustable trip classes and expanded diagnostic capability, and thermistor monitoring relays for direct winding-temperature protection via embedded PTC or NTC sensors. Current ranges span fractional-amp settings for small fractional-horsepower motors through 90A and beyond for larger industrial loads. When selecting an overload relay, engineers typically consider mounting compatibility, FLA adjustment range, trip class, reset method (manual vs. automatic), and whether separate or contactor-mounted installation is required.