MCB, RCCB and RCBO are common electrical protection devices used in a distribution board or DB box.
Although they may look similar, each device provides a different type of protection. Understanding the differences between MCB, RCCB and RCBO helps explain how electrical circuits are protected against overload, short circuit and residual or leakage current.
Note: The type, rating and arrangement of protection devices should be selected according to the circuit design and electrical installation requirements. Do not change circuit breaker ratings or protection devices without proper assessment.
What Is an MCB?
MCB stands for Miniature Circuit Breaker.
An MCB is used to protect an electrical circuit against overcurrent conditions such as:
- Overload – excessive load current above the normal operating level.
- Short circuit – a fault condition that can produce a very high current suddenly.
When an overcurrent condition occurs, the MCB can automatically disconnect the circuit to help protect cables and electrical equipment.
In a typical household DB box, several MCBs may be used to protect different circuits such as lighting, socket outlets and other electrical loads.
What Is an RCCB?
RCCB stands for Residual Current Circuit Breaker.
The function of an RCCB is different from an MCB. An RCCB detects an imbalance in current that may indicate residual or leakage current flowing to earth.
When the residual current exceeds the specified level, the RCCB can disconnect the supply. Residual current protection is an important measure for reducing the risk of electric shock caused by leakage current.
An RCCB does not provide overload or short circuit protection. It therefore needs to be used together with suitable overcurrent protection such as an MCB.
What Is an RCBO?
RCBO stands for Residual Current Circuit Breaker with Overcurrent Protection.
An RCBO combines residual current protection and overcurrent protection in a single device.
This means an RCBO can provide protection against:
- Overload – excessive load current.
- Short circuit – fault current caused by a short circuit.
- Residual current – leakage current flowing to earth.
In simple terms, an RCBO combines the protection functions normally provided by an RCCB and an MCB into one device.
Difference Between MCB, RCCB and RCBO
| Device | Main Function | Overcurrent Protection | Residual Current Protection |
|---|---|---|---|
| MCB | Protects the circuit against overload and short circuit | Yes | No |
| RCCB | Detects residual or leakage current | No | Yes |
| RCBO | Combines overcurrent and residual current protection | Yes | Yes |
Why Does a DB Box Use Different Protection Devices?
Each electrical circuit can have different cable sizes, loads, operating currents and protection requirements.
A properly designed DB box is therefore not simply fitted with the highest-rated circuit breakers. Each protection device needs to be suitable for the circuit and electrical installation it is protecting.
Factors that may need to be considered include:
- Cable size and type
- Design current of the circuit
- Type and amount of electrical load
- Residual current protection requirements
- Protection arrangement within the DB box
MCB, RCCB or RCBO – Which One Is Suitable?
There is no single protection device that is suitable for every electrical installation because MCB, RCCB and RCBO perform different functions.
An MCB provides overcurrent protection, an RCCB provides residual current protection, while an RCBO combines both functions in one device.
The appropriate device should be selected according to the circuit design, cable size, connected load and electrical protection requirements.
Do Not Increase the MCB Rating Without Checking the Circuit
If an MCB trips frequently, it should not simply be replaced with a higher ampere rating without first identifying the cause.
The circuit breaker rating is related to the circuit design, cable capacity and connected load. Using an unsuitable rating may result in the cable not receiving the protection it requires.
If your main problem is frequent power trips or circuit breakers that keep tripping, read our guide on why house electricity trips.
When Should a DB Box Be Checked?
A DB box should be inspected if there are signs such as frequent circuit breaker trips, heat or burn marks, damaged components, loose connections or a DB that is no longer suitable for the current electrical load.
An inspection can help identify whether the problem is related to the circuit, electrical load, protection device or the DB box itself.
If the DB requires replacement or improvement, see our DB box upgrade service.
FAQ
What is the main difference between an MCB and RCCB?
An MCB provides overcurrent protection against conditions such as overload and short circuit, while an RCCB detects residual or leakage current. They provide different types of electrical protection.
Is an RCBO the same as an MCB?
No. An RCBO provides overcurrent protection similar to an MCB but also includes residual current protection in the same device.
Does an RCCB protect against short circuit?
No. An RCCB is used for residual current protection and needs to be used together with suitable overcurrent protection.
Can I replace an MCB with a higher rating if it keeps tripping?
The MCB rating should not be increased without first checking the circuit. The protection rating needs to be suitable for the cable, connected load and electrical installation design.
Need an Electrical System Inspection?
If your DB box, circuit breakers or electrical system show signs of a problem, an inspection can help identify the actual condition before any components are replaced.
📲 WhatsApp us for an initial review of your DB box and electrical system.