These three devices appear together on almost every motor-control RFQ, and they are often confused. They do different jobs.
| Device | Main job | What to specify |
|---|---|---|
| MCB | Protects a circuit against overload and short circuit. Used for final circuits and control supplies; not meant for frequent motor switching. | Rating (A), poles, curve (B / C / D), breaking capacity (kA) |
| Contactor | An electrically operated switch for frequent on / off switching of motors and loads. It does not protect by itself. | AC-3 rating (A or kW), coil voltage, auxiliary contacts |
| MPCB | A circuit breaker designed for motors: adjustable overload plus short-circuit protection in one device. | Current setting range to cover the motor full-load current, breaking capacity (kA) |
How they work together
A typical direct-on-line (DOL) starter uses an MPCB for protection and a contactor for switching. An older arrangement uses fuses or an MCB for short-circuit protection with a contactor and a separate thermal overload relay.
Ordering replacements
- Match the make and frame of the existing device where panels are standardised
- For contactors, the coil voltage must match the control supply
- For MPCBs and overload relays, check the setting range against the motor nameplate full-load current
- Send the part number or a nameplate photo whenever possible
Published 30 September 2026 by Kanoi Traders.