Overload Relays

Shop thermal and electronic overload relays used to protect industrial motors from sustained overcurrent, excessive loading and phase-related operating conditions. Overload relays are commonly paired with contactors in motor starters for pumps, compressors, conveyors, HVAC equipment and industrial machinery.

Compare products by adjustable current range, trip class, reset method, mounting style and contactor compatibility. Always verify that the selected overload relay is electrically and mechanically compatible with the motor and associated contactor.

How to Select an Overload Relay

An overload relay monitors motor current and responds when an overload condition continues long enough to create excessive motor heating. It is normally installed with a contactor as part of a motor starter. An overload relay is not a substitute for the branch-circuit short-circuit and ground-fault protection required for the application.

Important Selection Factors

• Motor full-load current: Select an adjustable current range that includes the motor’s nameplate full-load current.
• Contactor compatibility: Many overload relays mount directly to a specific contactor frame, size or product series.
• Trip class: The trip class indicates how quickly the relay responds during an overload condition.
• Thermal or electronic design: Thermal relays use heat-sensitive elements, while electronic models may offer wider adjustment ranges and additional phase-protection functions.
• Reset method: Determine whether the application requires manual reset, automatic reset or a selectable reset mode.
• Auxiliary contacts: Verify the required normally open and normally closed trip-contact arrangement.
• Operating environment: Account for enclosure conditions, ambient temperature, vibration and applicable approvals.

Thermal vs. Electronic Overload Relays

Thermal overload relays are widely used for conventional motor-protection applications and typically provide an adjustable current setting with a mechanically operated trip mechanism. Electronic overload relays use current-sensing electronics and may provide broader adjustment ranges, improved phase-loss detection, selectable trip classes or other protective functions.

The best choice depends on the motor, starting characteristics, control system and required protection features. Do not assume that a relay with the same current range will fit an existing contactor or starter.

Replacement Checklist

When replacing an existing overload relay, record the following information before ordering:

• Manufacturer and complete part number
• Motor nameplate voltage and full-load current
• Single-phase or three-phase application
• Current adjustment range
• Trip class, when specified
• Manual or automatic reset requirement
• Associated contactor manufacturer and part number
• Mounting dimensions and terminal arrangement