What is the RCBO?


RCBO is a circuit breaker of the anti-shock circuit breaker group. So how does this device play a role in the electrical network. Let’s find out in the following article.

What is a shock absorber?

Anti-shock CB or anti-leakage circuit breaker … Anti-shock CB has the following types:

  • RCBO: Residual Circuit Breaker with Overcurrent protection.
  • RCCB: Residual Current Circuit Breaker.
  • ELCB: Earth Leakage Circuit Breaker

Anti-shock CB has the function of shutting off electricity when there is a leakage of electricity to the ground or someone is electrocuted. In addition, the RCBO, ELCB have the same overload protection function as the normal ones. Whereas the RCCB only has the function of preventing leakage current, need to combine with the MCB to protect the overload. For ease of visualization, RCCB + MCB = RCBO.

Functions of RCBO

1-phase RCBO

Single-phase RCBO compares the current flowing through two hot and cold wires. If this current differs by a certain leakage threshold, the RCBO will disconnect the power from the load, preventing the load from working. Manufacturers often design leakage thresholds of 15mA, 30mA, 100mA, 200mA, 300mA or 500mA.

RCBO 1 phase 30mA 40 50A Fuji Electric BC50E1CL 1N

RCBO 1 phase 30mA 40 50A Fuji Electric BC50E1CL 1N

3-phase RCBO

The 3-phase RCBO compares the current flowing through 3 phase and neutral wires. Similar to a 1-phase type, if this current differs from a certain leakage threshold, the RCBO will disconnect the power.

Structure, operating principle of RCBO in particular and Anti- shock CB in general

1-phase RCBO

Let the 2 hot and cold wires pass through a current transformer with a toroidal iron core. This is a common toroidal transformer with a primary winding of 1 coil (which is 2 cool and fire wires passing through the transformer center) and secondary winding with a few dozen turns.

The current that goes out on the hot wire on the cold wire and vice versa is the opposite. This means that the reciprocal magnetic field produced in the iron core of the current transformer is the opposite.

If these two currents are equal, the two reciprocal magnetic fields will cancel each other out as the output voltage of the secondary winding current = 0.

If the voltage across the 2 wires is leaked, the current on the 2 wires will be different. Then 2 reciprocal magnetic fields produced in different iron cores induce an inductive current on the secondary coil of the current transformer. This current is put into the IC to check whether it is greater than the safe leakage current. If larger (eg 15mA) the IC will supply power to Triac. Triac then supplies RCBO’s suction coil. It is not necessary to use ICs for detecting large leakage currents of several hundred mA (because IC circuits are complex and costly). At this time people use the electromagnetic force created when there is currently flowing in the coil to close the RCBO.

RCBO for 3-phase 3-wire power (3-pole 3-phase Aptomat Aptomat)

Same as above with 3 phase wires passing through the center of the current transformer.

RCBO for 3-phase 4-wire power (3-pole 4-pole Aptomat anti-shock)

Same as above with 3 phase wires and neutral wires passing through the center of current transformers.

Identification characteristics of RCBO

RCBO in particular and anti-shock circuit breaker in general have the same shape as normal CB. However, they are about the same size or a bit bigger.

Wiring for RCBO

  • Step 1: Shut off the power source and electrical system to ensure safety.
  • Step 2: Screw the RCBO into the electrical panel or panel, with a lid.

You should screw it firmly and carefully to avoid being loose during using electric equipment. Put the top of the line at the top, the top of the load at the bottom.

  • Step 3: Connect the power cord to RCBO:

When connecting wires to RCBO, AC power is attached to the line ends. The output attaches the subsidiary load to the load poles.

Do not re-attach as it will cause short-circuiting and danger to users. Hot wire must be connected to L pole, cold wire to N pole.

Note: RCBO without overload protection must be installed in series after MCB and MCCB to ensure the safety of the system when overloading and overvoltage occur.

  • Step 4: Complete the installation:

After installation is complete, you should not subjective use always, but need to check the electrical system to see if the RCBO works or not to adjust in a timely manner.

If the earthing is present, connect it to the cover of the load and then connect it to the ground. It doesn’t matter if there is no ground wire connected from the shell to the ground. RCBO still works normally.

In addition to the ON-OFF switch, RCBO also has a TEST button next to it to check if the device works well. On the front of the RCBO are listed parameters such as voltage, load current, impact time and leakage current. Normally there are leakage current thresholds of 15mA, 30mA, 100mA, 200mA, 300mA or 500mA.

RCBO 2 phase 30mA Fuji Electric BC50E1CL 2P 50A

RCBO 2 phase 30mA Fuji Electric BC50E1CL 2P 50A

Some notes when installing and using RCBO and other types of anti-shock CB

  • Must check the device before putting it into official use. During use you should check the device at least once a month to make sure it works well.
  • If RCBO is located in humid places such as bathrooms, near water heaters, washing machines, submersible pumps …, you should install a high-sensitivity switch or put RCBO in dry and cool places.
  • On days of high air humidity, RCBO will experience water condensation. The current thus leaks out. The relay will then completely disconnect the power automatically. Only when the air is dry again will the power source be restored. If not, we have to remove the relay.
  • Choose to buy equipment with famous brand, clear origin. You should also buy goods from reputable shops / agents / distributors to ensure benefits later.

Hopefully the above article has provided you with useful information about the RCBO. See you in the next posts.

Read more: What is a MCB?