MCB
Miniature Circuit Breaker
An automatic switch that turns a circuit off when too much flows, whether a slow or a sudden . It has replaced the rewirable fuse in modern boards. Each one is chosen by its current rating, such as 6 A for lights or 32 A for sockets, and by its type: B for most home circuits, C or D where equipment draws a big surge as it starts.
Where MCB fits in the learning path
The Installation section covers these units:
- Wiring Systems & Enclosures
- Cable Selection & Circuit Design
- Earthing, Bonding & Consumer Units
Curriculum mapping: C&G 2365 Units 203/204/305.
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This section is on the Plus path. Lesson availability depends on content review and your learning path.
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- Cable SizingInstallation
2. Try recalling, then explore practice
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- Cable Selection — quiz previewPlus · Installation
3. Return to the meaning
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Recall a related term
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Any current above the value a circuit is designed to carry. It comes in two flavours with different time scales: overload, where a healthy circuit is simply asked for too much for too long, and fault current, where a short circuit drives an enormous current that must be broken in milliseconds. Protective devices are chosen to handle both.
Overcurrent
Read the Overcurrent entryCompare related terms
Open a meaning to compare its role with MCB, or follow its full entry.
Overcurrent
Any current above the value a circuit is designed to carry. It comes in two flavours with different time scales: overload, where a healthy circuit is simply asked for too much for too long, and fault current, where a short circuit drives an enormous current that must be broken in milliseconds. Protective devices are chosen to handle both.
Read the Overcurrent entryRCBO — Residual Current Breaker with Overcurrent protection
A single DIN-rail device combining an RCD and a circuit breaker, so one module gives a circuit both residual-current protection and overload/short-circuit protection. The practical win is selectivity: a fault on one circuit trips that circuit alone, instead of dropping every circuit that shares a bank RCD.
Read the RCBO entryConsumer unit
The distribution board of a domestic installation. A main switch, residual-current protection and a row of circuit devices on a DIN rail split the incoming supply into individually protected final circuits. Modern UK consumer units sit in non-combustible enclosures and increasingly give every circuit its own RCBO instead of sharing RCDs across banks.
Read the Consumer unit entryA definition is a start. Using it in a real question is where it sticks.