How does a RCBO operate?

RCBO stands for Residual Current Breaker with Over-Current.
The RCBO combines the functionality of an MCB and RCD/RCCB. When there is a current leakage, the RCBO trips the entire circuit. Consequently, internal magnetic/thermal circuit breaker components can trip the electronic device when the circuit is overloaded.


Can RCBO work without earthing?

A RCD (aka RCCB or the RC part of the RCBO) works by adding the current flowing in the phase(s) to the current flowing in the neutral. If the total is not zero then you must have current flowing to earth.

Will a RCBO trip without a neutral?

With no neutral connection to the RCBO, there is no source of power for the internal detectors, so it will never trip - that is not a proper test, or a safe state to leave it in.


Are RCBOs better than RCDs?

RCDs and rcbos both provide additional protection as required by BS7671. An 30mA rcd provides additional protection only, but typically to a number of circuits. An rcbo provides additional protection, overload protection and short circuit protection to a single circuit.

Do I need an RCD if I have an RCBO?

RCD protection of all circuits with an RCBO.

Some RCDs in older installations may state 100mA and are not sensitive enough for modern standards - a 30mA RCD would be required as part of the extension lead.


What's the difference between an RCD and an RCBO? - Circuit protection.



Can you mix RCD and RCBO?

Yes, but only if there is not already an 30mA RCD covering the section of busbar you are mixing them on, ie dual RCD or split load board. On a main switch only board mix and match as you wish.

Why does the RCD switch keep tripping?

A faulty appliance is one of the main causes why RCD keeps tripping. Technically, RCDs are designed to protect against electrical circuit faults from faulty appliances. If an RCD trips, it has done its job and removed the faulty electrical circuit from the power network which could potentially cause a fire.

Can a MCB be used as a main switch?

Circuit breakers may work more effective as safe switches, but they are not switches. They are not interchangeable. Therefore, using a circuit breaker as a switch is not recommended.

How do you wire a Rcbo?

An RCBO can be installed as follows:
  1. Isolate the electrical supply from the consumer unit.
  2. Turn the two fasteners 90 degrees for detachment of the front cover.
  3. Carefully loosen the bottom terminal of the device.
  4. Open the bottom device clip.
  5. Position the device onto the din rail and busbar.
  6. Close the bottom device clip.


Does a 3 phase Rcbo need a neutral?

You can directly connect the 3 phase on 3 poles of RCCB (without neutral).

Will a 4 pole RCD work without neutral?

Answer: A 4-pole RCD will function correctly when connected into a 3-phase system without neutral. The residual current measurement and protection functionality does not rely on the presence of a neutral. The test button function simulates an earth leakage internally through a resistor.

What is the white wire on an RCBO?

The white cable is a reference earth.

If, however, the RCBO unit is a C60HC32R30 or similar, the white cable is a reference earth cable that enables the monitoring of the voltage to the neutral as a safety feature.

Where does the white cable go on RCBO?

The black is the load and goes L out, the white goes on N out. The bare wire stays where it was.


What is Fe on RCBO?

The Functional Earth (FE - white wire) connection to the RCBO seems very delicate - less than 0.5sqmm.

Why does RCD trip but not MCB?

If the insulation failure is catastrophic, a large current will flow and both the RCD and circuit breaker may trip. However, if the leakage to earth is small, well below one amp, then the circuit breaker will not react, but the RCD will react to any leakage current over 30mA.

Why does my RCD trip when it rains?

When it rains, water can make its way into the cord, cause a short and trip the breaker. Interior extension cord-Indoor extension cords ends aren't made to be water-tight. So after a good rain, water can get in the cord and cause the tripping breaker.

Why do both RCDs trip?

RCDs trip when a fault is detected in an electrical circuit. When an RCD trips frequently (even after resetting), it is probably responding to a damaged electrical appliance. This means your switch is working correctly.


Which circuits should not be RCD protected?

For new installations and rewires, all socket-outlets with a rated current not exceeding 32A need to have additional protection by RCD, except where other than for an installation in a dwelling, a documented risk assessment determines that the RCD protection is not necessary.

Can you run an RCD off an RCD?

RCDs aren't current limiting so you can't discriminate on residual current rating alone - e.g. a 1A fault will likely trip out both.

Do bathroom lights need to be RCD protected?

Electric showers require their own electrical circuit, which in general will have the highest electrical demand out of your household appliances. All circuits in a bathroom must be protected by a RCD (Residual Current Device).

Can I replace RCBO with MCB?

If that is the case in your gaff, replacing one lighting circuit mcb with an RCBO would cause it to trip (shared neutral). Replacing both would not prevent this either, you would have to put both circuits on the one RCBO.


Can RCBO be used as MCB?

MCB can provide protection against overcurrent and short circuit only while RCBO can provide protection against overcurrent and earth leakage. MCb can not protect against earth faults while in RCBO can protect against earth fault, electric shocks that MCB may not do.

What are the different types of RCBO?

Type A - Can be used for general purpose and for equipment incorporating electronic components. The RCD can detect and react as Type AC as well as accommodate pulsating DC components. Type F - Used for appliances containing synchronous motors and some class 1 power tools.