What is RCBO? How does it work in 2023

What is RCBO? How does it work?

Friends, RCBO stands for something like Residual-current Circuit Breaker with Overcurrent protection. This means that it carries out two important functions. As a circuit breaker, it is designed to protect the circuit to a rated amperage as designated on the RCBO.

An RCBO is in other terms a combined Miniature Circuit Breaker (MCB) and Residual Current Device (RCD).

An RCBO is in other terms a combined Miniature Circuit Breaker (MCB) and Residual Current Device (RCD). RCBO stands for something like Residual-current Circuit Breaker with Overcurrent protection. This means that it carries out two important functions.

As a circuit breaker it is designed to protect the circuit to a rated amperage as designated on the RCBO. But a circuit breaker alone is not designed to protect people from electric shocks and short circuits, which could kill you.

RCDs, on the other hand, measure the amperage on the active and neutral wires, and if there is a discrepancy (usually 30mA is the designated threshold) which could be from a person causing a short circuit through themselves, it will trip the breaker in 0.03 seconds. This is usually quick enough to protect someone from electrocution.

As far as I understand it is a requirement in Australia to protect all circuits — both power and light circuits — with RCDs, but you also need a circuit breaker to protect the actual circuits from drawing too much current on the appliance side, which could damage the wiring and cause fires.

Simply put, an RCBO combines both of these devices into one to avoid needing two separate devices per circuit.

An RCBO is a type of circuit breaker with two functions.

To protect life
To protect an overload on a circuit – overcurrent and short circuit

Electricians will install an RCBO (Residual Current Breaker with Overcurrent) where there is a need to prevent overload on a particular circuit at the same time as preventing anyone getting a shock that has the potential to kill them.

An RCBO will normally have two circuits for detecting an imbalance and an overload but use the same interrupt method (breaker or trip).

It works in a similar way to an RCD measuring the current on the live and neutral conductors. If they are not equal it suggests there is current leakage to earth, which could potentially mean someone is standing on their bed with their finger touching the live conductor of a light as they are attempting to change a light bulb – the RCBO will break the ciruit or trip.

RCBOs (combined MCB/RCD) – Single module, nominal rating 6 A
Breaking capacity: 10 kA to BS EN 61009-1
RCD type AC conform to BS EN 61009-1
Terminal capacity: rigid conductor 35 mm²; flexible conductor 25 mm²
Single pole and neutral – 240 V±

An RCBO also works as an MCB (Minature or Mains Circuit Breaker). In this operation, it is designed to interrupt a current overload in a circuit. RCBOs are rated both by the normal current that is expected to carry, and the maximum short-circuit current that they can safely interrupt.

A short circuit is an abnormal low-resistance connection between two nodes of an electrical circuit that are meant to be at different voltages, for example, if a conductor liquid (water, coffee, tea, etc) causes a connection between the live and neutral terminals of a plug or a light switch. This is one of the reasons you will have a pull cord in the bathroom.

Residual Current Circuit Breaker with Over Current Protection RCBOs

This is a protective device that combines two functions. It acts as a residual current device and a circuit breaker. A circuit breaker breaks the circuit if the current demand gets too high.

How?

The circuit breaker is set at the capacity of the wires in the circuit it protects. If there is an overload caused by e.g. a short circuit or excessive demand caused by plugging in too many devices on the same circuit, it reacts. Without this protection, the wires could melt and catch fire.

Circuit breakers protect equipment and buildings.

The range designed to ensure efficiency and protection RCBOs are commonly used in applications where there is the need to combine protection against overcurrents (overload and short-circuit) and protection against earth leakage currents.

RCBOs help in sensing this kind of fault and trip the circuit ensuring complete protection of the people and connected types of equipment.

Main benefits

High quality
Complete range

Main Features

AC, A, AP-R type available
Wide range of breaking capacities for application from residential to the industrial field
Rated Currents up to 125 A and poles configuration for applications in Single Phase as well as Three Phases networks
Sensitivities up to 1000 mA

What is the major difference between RCCB and RCBO?

First, let us know about ‘RCD’ or in expansion ‘Residual Current Device’. This is the one that is commonly used for the Incomer in India.

Now, we can say simple, RCCB (Residual Current Circuit Breaker) and RCBO (Residual Current Breaker with Over Load Protection) are two sub-class of RCD.

The major difference between an RCCB and RCBO is, an RCCB provides only leakage protection, were as RCBO provides, “over load+short circuit+leakage protection”. That means an RCBO is a combination of RCCB and MCB.

Characteristics of RCCB-Rated Current and Sensitivity
Characteristics of RCBO-Rated current, Tripping characteristics (B, C & D), and Sensitivity.
Available ratings of RCCB=10,16,20,25,32,40,63,80/100
Available ratings of RCBO=16,20,25,32,40,63,80/100.

An RCCB is (in practical terms) another name for an RCD. So is ELCB. These days they are all current operated.

You know what an MCB is?

Well, an RCBO is a single device which combines the functions of an MCB (overcurrent and short-circuit protection) and an RCD (Earth leakage protection).

The better makers offer a range of them, so you can have a B32 30mA RCBO for example for your socket circuits, or a B40 30mA for your shower. As far as I know, MEM make the widest range possible, because of the way they are assembled. You can order a D6 100mA, if you want.

They can generally be fitted into a Consumer Unit in place of an MCB. Some are the same width, others are wider and may take up two spaces. this depends on the brand and model.

In domestic consumer units, they will generally cut one pole only (the Phase conductor) although two-pole RCBOs are available to cut Phase and Neutral.

They tend to be quite expensive. However, in the respect that, in the event of earth leakage, they will cut power only to the affected circuit without inconveniencing users on other circuits, they are superior to a split-load arrangement or an installation protected by a single RCD, because either of these will cut power to the other circuits.

Quite apart from the inconvenience, this makes them valuable in commercial and industrial environments, because it prevents you from losing production on those other circuits. This can save you a lot of money.

Which is better to use for home wiring, RCCB, or RCBO, and why?

An RCCB is useful for detecting phase and neutral current imbalance, with the imbalance level typically being 30mA in a domestic installation.

However it will NOT detect overload in the branch circuit in which is connected, so an additional thermal-magnetic circuit breaker (MCB) will be required in each branch circuit.

An RCCB in a domestic switchboard is typically rated at 40A and so can be used upstream of up to three 16A MCBs.

An RCBO has the same current imbalance protection as a RCCB, but also has overload protection similar to that of an MCB. RCBOs have an overload current rating range the same as that of MCBs, so a separate MCB is not required in each branch circuit.

The advantage of using RCCB plus MCBs is cost. Even though more devices are needed, the total cost ends up being less than that of using RCBOs.

The disadvantages of using RCCB plus MCBs are:

An earth fault in one branch circuit will cause one or more other branch circuits to additionally trip. This is likely to be a nuisance.
Because additional devices are required, the area taken up in the distribution board will be greater.

The advantages of using RCBOs in each branch circuit are:

If an earth fault is detected in one branch circuit, only that branch will trip. Other circuits will not (should not) be affected.
Fewer devices will be required in your switchboard, so it can potentially be smaller.

The disadvantage of using RCBOs in each branch is cost. RCBOs are pricey little gadgets and using them will be more expensive than the RCCB / MCB option.

Definition

RCBO stands for ‘Residual Current Breaker with Over-Current’. As the name suggests it protects against two types of fault and in essence combines the functionality of an MCB and RCD.

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