Switch and Circuit Breaker Types: MCCB vs Load Break Switch vs ACB vs Motor Protection Breaker
Moulded case breakers, air circuit breakers, motor protection breakers, load break switches, cam and transfer switches compared; breaker vs disconnector, Icu, Ics and pole choice.
A switch opens and closes an electrical circuit by hand or automatically. The first question in selection is whether the device only switches and isolates, or also protects by tripping on overcurrent and short circuit. Devices that protect are circuit breakers (IEC 60947-2); those that do not are load break switches and switches (IEC 60947-3).
> Related Category: Browse all types and ratings in Switches, Molded Case Circuit Breakers and Load Break Switches.
1. Switch types compared
| Type | Current range | Protection | Use |
|---|---|---|---|
| Moulded case circuit breaker (MCCB) | 16–1,600 A | Overload + short circuit | Main and sub-board incomers, feeders |
| Air circuit breaker (ACB) | 630–6,300 A | Electronic, adjustable, selective | Transformer output, main switchboard incomer |
| Motor protection circuit breaker (MPCB) | 0.1–100 A | Adjustable thermal + magnetic, phase loss | Protection and manual control of one motor |
| Load break switch | 16–3,150 A | None | On-load switching, isolation for maintenance |
| Fuse switch-disconnector | 32–1,250 A | By NH fuses | Fused protection instead of an MCCB |
| Cam switch | 10–200 A | None | Machine main switch, 0-1, 1-0-2, star-delta |
| Transfer switch | 16–3,200 A | None (used with breakers) | Mains–generator changeover; manual or automatic |
| Modular switch | 16–125 A | None | DIN-rail isolation and control inside boards |
2. What is an MCCB?
A circuit breaker in a moulded insulating case holding contacts and trip unit together. It trips by itself on overload and short circuit and is reset once the fault is cleared.
| Trip unit | Adjustment | Use |
|---|---|---|
| Thermal-magnetic, fixed | None | Small feeders |
| Thermal-magnetic, adjustable | Thermal 0.7–1 × In, magnetic 5–10 × In | General distribution |
| Electronic | Long, short and instantaneous settings plus earth fault | Incomers needing selectivity, generators |
The toggle has three positions: on, off and a middle trip position. After a trip, pull the toggle fully down to reset, then close. For the difference from a miniature breaker see MCB vs MCCB Circuit Breaker Difference.
3. Air circuit breakers
Open-type power circuit breakers for high currents have a metal frame, stored-energy spring mechanism and usually a withdrawable design. They can carry short-circuit current for a set time (0.5–1 s) without tripping, letting the downstream breaker clear the fault first. This is the short-time withstand current (Icw) and is the basis of selectivity.
4. Load break switch vs circuit breaker
| Property | Load break switch | Circuit breaker (MCCB, ACB) |
|---|---|---|
| Switches rated current | Yes | Yes |
| Breaks short-circuit current | No | Yes |
| Trips by itself on overcurrent | No | Yes |
| Visible or reliable isolating position | Yes | On types suitable for isolation |
| Needs upstream protection | Yes (fuse or breaker) | No |
A load break switch isolates a circuit safely for maintenance and its handle can be padlocked. As it gives no protection, a fuse or breaker must always sit upstream. Fused versions combine protection and isolation; fuse types are covered in Fuse Types.
5. Motor protection, cam and transfer switches
- Motor protection circuit breaker: set the thermal dial to the motor nameplate current; the magnetic trip at about 13 × In lets starting current pass. See MPCB vs Thermal Overload Relay.
- Cam switch: a rotary cam-operated switch with no protection. Depending on its switching diagram it does on-off, reversing or star-delta. See Rotary Cam Switch Wiring.
- Transfer switch: changes between two sources (mains and generator) without ever connecting both to the load. Available manual (1-0-2) or motorized with automatic control; choose 4 poles so the neutral is switched too.
6. Selection criteria
| Criterion | Meaning | Rule |
|---|---|---|
| In (rated current) | Current carried continuously | Load current ≤ In ≤ cable current-carrying capacity |
| Icu (ultimate breaking capacity) | Highest short-circuit current it can break | Above the prospective fault current at the point of installation |
| Ics (service breaking capacity) | Current after which it stays in service; 25–100% of Icu | Prefer Ics = 100% Icu on incomers |
| Icw (short-time withstand) | Current and time carried without tripping | Upstream levels where selectivity is required |
| Poles | 3P or 4P | 4P in TT and generator systems where the neutral must be isolated |
- Selectivity: only the breaker nearest the fault should trip; set the upstream breaker's current and delay above the downstream one.
Frequently asked questions
What is an MCCB?
A moulded case circuit breaker. It trips by itself on overload and short circuit across 16–1,600 A and is used on board incomers and large feeders.
What is the difference between an MCCB and a load break switch?
An MCCB breaks short-circuit current and protects. A load break switch only switches rated current and isolates for maintenance; it cannot break a short circuit and needs a fuse or breaker upstream.
When is an air circuit breaker used?
On main incomers above 630 A and at transformer and generator outputs. Its short-time withstand rating gives selectivity with downstream breakers, and the withdrawable design eases maintenance.
Should a breaker be 3-pole or 4-pole?
Use 4 poles where the neutral must be isolated with the phases: TT systems, mains–generator changeover and incomers with residual current protection. Use 3 poles in TN-C systems where the neutral is not switched.
What do Icu and Ics mean?
Icu is the highest short-circuit current the breaker can interrupt once. Ics is the current after which it can remain in service, given as a percentage of Icu.