Short answer: A motor protection circuit breaker (MPCB) is a manual motor starter – one device that isolates, protects against short circuit and protects against overload, and is often also called on to detect phase loss. It replaces the relay-plus-contactor pair for small and medium motors, and it is set close to the motor’s full-load current rather than to the branch rating. Buy it when panel space, wiring simplicity or a single isolation point matter; keep the pair when you need a large frame or a specific coil frequency.
HAZAM is an independent trading company – not a manufacturer, and not an appointed distributor of any brand. What follows is how an MPCB is applied on the starters we quote, and how it differs from the two-part solution it replaces.
What an MPCB actually is
The name is a description, not a standard. The product is a compact device for a single motor branch that combines four jobs in one moulding: a manual means of isolation, a magnetic short-circuit trip, a thermal overload trip with an adjustable setting, and – in the versions we quote – phase-loss detection engineered to release the mechanism. Because it carries the motor current itself and switches it manually, it is properly a manual motor starter, declared to IEC/EN 60947-2 for the short-circuit duty and to IEC/EN 60947-4-1 for the motor-switching duty.
That dual declaration matters at quotation time. A device that is only a supplementary protector is not the same product as one declared for motor starting, and comparing the two on price alone is comparing two different jobs.
Three ways to protect a motor
| Approach | What it gives you | Where it fits |
|---|---|---|
| MPCB alone | Isolation, short-circuit and overload in one device; manual start | Small and medium motors started by hand, or where a contactor is added for remote control |
| Contactor + thermal relay | Remote switching by the contactor; protection by the relay | Larger frames, frequent remote starts, and grids needing a specific coil frequency |
| MCCB + separate protection | Short-circuit protection at a higher frame, protection added downstream | Very large motors and feeder protection where the branch device is a moulded case breaker |
The MPCB sits in the middle of that table. It is the economical answer for a panel with many small motor branches, because one device per branch replaces two and the wiring becomes a single line. The heavier options above it are not worse – they are for duties the compact device cannot carry.
The two trips: thermal and magnetic
An MPCB has two independent tripping elements, and knowing which is which explains why the setting is not simply the motor current.
The thermal element is adjustable across a band and is where you set the motor’s full-load current. It protects the winding against sustained overcurrent and is the number you turn on the dial.
The magnetic element is factory-set and is not adjustable. It clears a short circuit quickly. Because it is fixed, the device is chosen so that its magnetic threshold sits above the motor’s normal starting current – a value well above the full-load current. This is also the reason two devices with the same thermal band can differ in price: the short-circuit rating and the magnetic behaviour are part of the part number, not a dial you can turn.
Phase-loss protection is the third behaviour and the one buyers most often forget to ask about. On a three-phase motor a single lost phase raises current in the remaining windings very fast; a device that detects the loss trips ahead of the overload curve, which is exactly what a motor branch is being protected against.
Type 1 and Type 2 coordination
IEC/EN 60947-4-1 defines two levels of coordination between the short-circuit device and the contactor or starter it protects, and the level you specify changes what survives a fault.
| Coordination | After a short circuit | Practical meaning |
|---|---|---|
| Type 1 | No danger to the operator; the device may be damaged and need replacement | The cheapest honest answer for a branch that is rarely faulted |
| Type 2 | No damage except light welding of contacts that separates easily; the device stays serviceable | Specified where downtime after a fault is the real cost |
Coordination is a tested combination, not a calculation: the short-circuit device, the starter and the rating all belong to a declared table. When you move a motor branch from one brand of breaker to another, the coordination table must be re-checked – a point that also applies when replacing an international-brand starter with a CHINT device, as set out under cross-reference.
Sizing in five steps
- Fix the motor. Nameplate power, full-load current, connection (delta or star) and supply voltage. These set the thermal setting.
- Confront the starting duty. Starting current, run-up time and starts per hour decide whether a compact device is enough or a higher class is needed.
- Choose the frame. Match the thermal band to the full-load current near its middle, and confirm the frame’s short-circuit rating is adequate at the prospective fault level at that point – stated per frame and voltage in the catalogue.
- Set the coordination target. Decide Type 1 or Type 2, then take the combination from the tested table rather than assembling it by eye.
- State the grid. Frequency decides the coil of any contactor used with the MPCB, and the protection curves are declared at a stated voltage. Give voltage, frequency, phase and destination.
The NS2 range
NS2 is the CHINT manual motor starter family we quote for this duty. It is declared to IEC/EN 60947-2 and IEC/EN 60947-4-1 for AC-3 motor duty up to 690 V, with frames covering 0.1-32 A of thermal setting for the NS2-25 and NS2-32, and an NS2-80 frame in the catalogue. The thermal trip is adjustable across the band; the short-circuit protection follows 60947-2 and is stated per frame and voltage. It is offered in a three-pole version with a CE certificate published for the NS2-25.
Where the motor is larger than the compact range covers, the answer returns to the pair: an NXC contactor with an NXR overload relay, or a moulded case breaker for the largest motors. The relay side of that solution is set the same way as any thermal relay, as described in setting an NR2 overload relay.
Common mistakes
Three errors recur on motor branches. First, setting the dial to the branch or cable rating instead of the motor current, which under-protects the motor. Second, treating a voltage or phase-monitoring relay as if it were an MPCB – a monitoring relay senses the supply and trips a contactor, but it does not carry or interrupt the motor current, so it cannot replace the starter. Third, assuming an MPCB replaces a contactor: it can start a motor by hand, but a remotely controlled or frequently started motor still needs a contactor, with the MPCB protecting the branch.
For the short-circuit device above a motor branch, and for the frame logic behind it, see MCCB selection and moulded case circuit breakers. Panel layout, including the space a starter takes, is covered under how to size a distribution board.
FAQ
Q: Is an MPCB the same as a thermal overload relay?
A: No. A thermal overload relay only protects against sustained overcurrent and must be paired with a contactor for switching and with a breaker or fuse for short-circuit protection. An MPCB combines isolation, short-circuit and overload protection in one device.
Q: At what current do I set an MPCB?
A: To the motor’s full-load current at the connection in use, the same rule as any thermal overload device, with the band chosen so that current falls near the middle. The magnetic trip is separate and factory-set.
Q: Can an MPCB start the motor by itself?
A: It can be operated by hand as a manual starter. If the motor must be started remotely, frequently, or from a control system, add a contactor and let the MPCB protect the branch.
Q: What is Type 2 coordination and why does it cost more?
A: Type 2 means the starter is still serviceable after a short circuit, with only light contact welding that separates easily. It is a tested combination of devices and ratings, so it constrains the parts you may use and is specified where downtime is expensive.
Q: Does an MPCB include phase-loss protection?
A: The versions we quote do, and it is worth asking about explicitly. Losing one phase on a three-phase motor raises the current in the other windings quickly, and a device that detects the loss trips ahead of the overload curve.
Q: Does the destination grid change the selection?
A: The protection curve is declared at a stated voltage, and any contactor used with the device needs a coil wound for the local frequency. Quote voltage, frequency, phase and destination and the selection stops being a guess.
Related: Contactors, overload relays and starters · Setting an NR2 overload relay · AC-1 vs AC-3 vs AC-4 contactor selection · MCCB selection: frame, breaking code, trip unit · Schneider, ABB, Siemens to CHINT cross-reference · How to size a distribution board · Request a quotation