Collection: Motor Protection Switches

A motor protection switch is a combined device that protects a motor circuit against thermal overload (caused by sustained overcurrent or blocked rotor) and short-circuit faults. Unlike a basic MCB circuit breaker, it has an adjustable current dial calibrated for motor inrush, so it won't trip on start-up but will trip reliably on damaging overloads.

Standard MCBs have fixed trip curves (B, C, D) designed for resistive or general loads. A motor protection switch has an adjustable overload setting and a trip curve optimised for the high inrush current of motor starts, avoiding false trips while still responding quickly to a genuine fault. It also typically offers a higher switching duty cycle for motor loads.

Check the motor's nameplate for its rated current (FLC) in amperes. Turn the adjustable dial on the motor protection switch to match this value within the switch's range. Do not set it higher than the motor's rated current — this would reduce protection effectiveness. For guidance on complementary overcurrent devices, see the full Fuses & Electrical Protection range.

No. A motor protection switch is a protective and manual isolation device, not a contactor. Contactors are designed for frequent switching duty (many thousands of operations) and remote/automated control. In a standard motor starter circuit, the motor protection switch is wired in series upstream of the contactor, providing fault protection while the contactor handles operational switching. Combining both gives complete electrical protection for the motor.

Yes, most motor protection switches are available in three-pole versions specifically designed for three-phase motor circuits, offering phase-loss detection in addition to overload and short-circuit protection. Single-pole versions exist for single-phase applications. Always verify the voltage rating and pole count match your installation. For additional upstream protection, consider Residual Current Devices (RCCB).

Phase-loss protection trips the switch when one phase of a three-phase supply is lost. Running a three-phase motor on two phases causes it to draw very high current on the remaining phases, rapidly overheating the windings. A motor protection switch with phase-loss detection responds faster than standard overload protection, preventing motor burnout. This feature complements glass and cartridge fuses used for upstream short-circuit protection.

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