How to find the right Overload Relays AI guide

What the AI looks for in Overload Relays

Contactor family match

Buy the overload made for your exact contactor series and frame size (for example Schneider TeSys LRD for LC1D, Siemens 3RU or 3RB for 3RT, Eaton XTOB for XTCE, ABB TF or EF for AF, Allen-Bradley 193 for 100-C). Overloads plug directly onto the contactor's terminals, and cross-brand fitment generally does not work.

Current setting range

The motor's nameplate full-load amps must fall inside the dial range, preferably not at either extreme. Set the dial per the motor nameplate and service factor as the local electrical code requires. A range that is too high never trips. One that is too low trips on normal running current.

Trip class

Class 10 suits most standard motors. Class 20 or 30 suits high-inertia loads with long acceleration times. Too fast a class nuisance-trips on start, and too slow a class lets the motor overheat.

Thermal (bimetal) or electronic

Electronic overloads give wider adjustment ranges, better phase-loss sensitivity and no ambient drift. Bimetal units are cheaper and simpler. Electronic units also cover more FLA with fewer part numbers.

Reset mode and auxiliary contacts

Choose manual or automatic reset to suit the application, and use the NC auxiliary contact in the contactor coil circuit. Automatic reset can restart machinery unexpectedly, and the NC contact is what actually stops the motor.

Single-phase use

On single-phase or DC motors, wire the current through all three poles as the manufacturer's diagram shows. Otherwise phase-loss detection trips the relay immediately.