An overload relay is part of the motor protection and control arrangement, not simply an accessory attached to a contactor. A replacement must match the motor current range, trip behavior, reset method, phase protection, mounting interface, and the surrounding branch-circuit components.
Before sending an industrial overload relay replacement RFQ, identify the motor, starter or contactor, relay technology, settings, and fault behavior. A relay with a similar current dial or matching frame can still be unsuitable for the installed application.
1. Identify the motor circuit and protection role
Record the motor or load controlled by the starter: pump, fan, conveyor, compressor, machine tool, or another industrial load. Capture the motor nameplate voltage, full-load current, frequency, power, service factor, starting method, and whether the application is single-phase or three-phase.
Note the contactor, short-circuit protective device, motor starter, drive or soft starter, PLC feedback, and reset circuit around the overload relay. The KNMKS Relays & Interface category and product directory can help organize the existing device and motor-system references before an inquiry.
2. Capture the complete relay identity
Photograph the relay label, current setting dial, trip-class marking, terminal numbers, reset selector, test button, and mounting interface. Record the complete manufacturer reference, suffix, revision, and the contactor or starter family to which it is attached.
Determine whether the device is a bimetallic thermal relay, electronic overload relay, motor protection controller, or an integrated starter component. Record whether the relay requires a separate heater element, current transformer, mounting adapter, or communication accessory. Similar housings can hide different sensing and control methods.
3. Verify current range and motor settings
Record the relay adjustment range and the actual setting used in the cabinet. Compare the setting with the motor nameplate full-load current and the documented commissioning values. Do not select a replacement only from the maximum current printed on the front.
Check whether the relay uses a fixed thermal unit, an adjustable dial, electronic current measurement, or a motor controller with configurable parameters. Rockwell Automation documentation covers electronic and bimetallic overload relay specifications and motor protection references. See the Rockwell Automation overload relay documentation.
4. Confirm trip class and application duty
Record the trip class, start duration, acceleration profile, and expected number of starts per hour. A high-inertia load, frequent restart, or long acceleration time can require a different protection response from a lightly loaded motor.
Document the existing trip behavior and the reason for replacement. A relay that trips during starting may reflect a setting, load, motor, or coordination issue rather than a failed relay. The replacement request should distinguish a component failure from a requirement to change motor protection.
5. Check phase-loss and fault functions
Record whether the overload relay provides phase-loss sensitivity, current imbalance detection, jam or stall protection, ground-fault functions, thermal memory, or another diagnostic feature. For an electronic relay, capture the display, alarm outputs, communication option, and fault history if available.
Also check the auxiliary contact arrangement and normal state. Note which contact opens the contactor coil circuit and which contact reports a trip to the PLC or HMI. A replacement with a different auxiliary arrangement can change both shutdown behavior and the alarm shown to operators.
6. Verify reset and mounting compatibility
Record manual, automatic, remote, or monitored reset behavior. Check whether the reset button is accessible after the starter is installed and whether the control circuit expects a specific contact transition. Confirm whether reset mode changes after a power cycle or trip.
Measure the mechanical interface: contactor frame, mounting clips, terminal orientation, line and load side, accessory slot, cabinet clearance, and wiring space. An overload relay designed for a related contactor family may not mount directly or may require a different adapter.
7. Review coordination with branch protection
Overload protection and short-circuit protection perform different functions. Schneider Electric documentation explains that an overload relay protects against prolonged motor overcurrents, while fuses, circuit breakers, or motor short-circuit protectors address higher fault currents. Record the upstream protective device and the documented coordination so the replacement is reviewed as part of the complete branch circuit.
Do not claim that a larger adjustment range automatically improves protection. The correct setting and coordination depend on the motor, starter, application, and applicable engineering requirements. Use the Schneider Electric overload relay technical paper for reference terminology.
8. Prepare a complete RFQ checklist
- Complete overload relay model, suffix, revision, current range, and trip class.
- Motor nameplate, starter or contactor model, supply voltage, current, frequency, and duty.
- Actual current setting, reset mode, phase-loss function, diagnostics, and auxiliary contacts.
- Mounting interface, heater or adapter requirements, terminal orientation, and cabinet photos.
- Upstream short-circuit protective device, PLC feedback, fault history, and application notes.
- Quantity, destination country, replacement or project use, and required timing.
If the model is unclear, send the relay and motor nameplate photos together with the contactor reference. The KNMKS ABB brand reference can provide an additional entry point when the starter belongs to an ABB ecosystem.
Final replacement gate
Before approving an overload relay replacement, confirm the motor current, adjustment range, trip class, sensing technology, phase protection, reset behavior, auxiliary contacts, mounting interface, and branch coordination. A matching contactor frame or current dial does not establish equivalence. If one point is uncertain, keep the request at model-review stage and provide the missing label or motor photo.
KNMKS supports model-based inquiries for overload relays, contactors, motor starters, and industrial control equipment. Send the exact references, motor data, cabinet photos, quantity, destination, and application notes for a compatibility-focused RFQ review.
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