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How to Wire an RCBO? Residual Current Breaker with Overcurrent

Wiring a 1P, 2P & 3P RCBOs – Residual Current Breaker with Overcurrent Protection

A Residual Current Breaker with Overcurrent Protection (RCBO) is a protective device that safeguards electric circuits and appliances from both short circuits/overcurrents and leakage/earth faults. It incorporates features of both Miniature Circuit Breakers (MCBs) and Residual Current Devices (RCDs or RCCBs). In today’s post, we will show how to wire 2-P, 3-P and 4-P RCBOs for different load circuits.

The RCCB unit senses current imbalances in both the phase and neutral wires, detecting leakage faults, while the MCB unit protects against short circuits and overcurrents.

Good to Know:

  • An RCBO combines the functions of both an MCB and an RCCB; in other words, RCBO = MCB + RCCB (RCD).
  • The wiring connection of an single pole RCD and RCBO is the same as wiring a Ground Fault Circuit Interrupter (GFCI) and Arc Fault Circuit Interrupter (AFCI).
  • The GFCI (Ground Fault Circuit Interrupter) in North America and Canada is the same as the RCD or RCCB (Residual Current Breaker or Residual Current Circuit Breaker) in the UK, EU, and Australia.
  • Wiring the 1-Pole RCBO (UK & EU – IEC) is the same as wiring a GFCI (US – NEC).

Related Post: How to Wire 1-Phase Split Load Consumer Unit? – RCD+RCBO

Why to Use RCBO instead of MCB or RCD?

Using an RCBO is a suitable option instead of an RCD or MCB. In the case of a leakage or earth fault, the RCD will trip and disconnect all circuits connected to it until the fault issue has been resolved. In contrast, the RCBO will only interrupt the dedicated circuit connected to it, allowing the rest of the circuits to work reliably and smoothly.

In addition, it is a wise decision to use, when applicable, a single unit of RCBO that offers the functions of both RCD and MCB in a single device. This is particularly beneficial when space in the consumer unit / DB is limited for additional or existing breakers

In the following wiring tutorial, we will demonstrate how to wire single-pole, two-pole, and four-pole RCBOs in distribution boards and consumer units for both single-phase 230V and three-phase 415V AC supplies.

How to Wire 1-Phase, 1-Pole RCBO?

The following diagram shows the wiring connection of a 1-pole RCBO for single-phase, 230V AC – (1P + N) load points.

How to Wire an RCBO Residual Current Breaker with Overcurrent

As shown, the two built-in wires (blue and white) should be connected to the main neutral terminal block and earth terminal block in the consumer unit or distribution board. The Line terminal (1) should be connected to the line wire from the main MCB. The lower terminals of L and N should be connected to the single-phase load points, such as socket outlets.

Single Pole RCBOs in Consumer Units and DBs

The following wiring diagram illustrates a split-load consumer unit where some load points are protected by RCBOs, while the rest are protected by RCDs and MCBs.

Click image or open in new tab to enlarge

How to Wire a 230V Split Load Consumer Unit - RCD+RCBO - IEC & UK

Similarly, the next wiring diagram shows that the washing machine and standard outlet are connected and protected by RCBOs, while the LED lamp and ceiling fan are connected and protected by an MCB and an RCD.

Click image or open in new tab to enlarge

Wiring Single Phase Circuits in a Split Load Consumer Unit for RCD & RCBO

How to Wire 1-Phase, 2-Pole RCBO?

The two-pole RCBO can be wired the same way as a generic 2-pole MCB or an RCD. As shown in the figure, the 230V single-phase supply from the main MCB or RCD in the consumer unit/distribution board is connected to the input terminal of the RCBO via the Line and Neutral wires.

Wiring 2-Pole RCBO

Similarly, the output terminals of the RCBO are connected to the load point, such as a standard socket, via outgoing Line and Neutral wires.

How to Wire 3-Phase, 4-Pole RCBO?

The following wiring diagram shows the Three-Phase Four-Pole RCBO (3P + N) used to protect a hot water spa.

Wiring a Three Poles RCBO (MCB + RCB or RCD)Circuit Breaker

As illustrated in the wiring diagram, the three-phase lines (L1, L2, and L3) from the consumer unit MCBs are connected to the upper terminals of the 4-pole RCBO. The neutral wire must also be connected to the “N” input terminal.

Similarly, all three-phase (hot or live) wires, along with the neutral wires, are connected to the three-phase 415V AC spa control box. Finally, the ground wire is connected to the load terminal box.

For 3-phase spa wiring, use #10 or a minimum of #12 gauge for each line conductor. For instance, use 4.0mm2 (#12 gauge) for each phase wire for loads up to 12kW, with a 3-phase 415VAC configuration. In the case of higher wattage, refer to the table in the manual for the appropriate wire size.

Good to Know:

  • Type “A” RCBOs do not detect smooth DC (pulsating DC < 6 mA).
  • Type “AC” RCBOs are not recommended for use in electronic-based or sensitive applications.
  • Type “AC” RCBOs should be connected downstream (not upstream) of Type A, F, B, or EV RCDs.
  • 1-pole RCBOs (1P + N) are not recommended for computer and IT applications.
  • Use a 1P RCBO with a 1P MCB/RCD, a 2P RCBO with a 2P MCB, and a 3P RCBO with 3P MCBs.
  • In a 3-Phase, 4-Wire System, a 3P + N RCBO must be connected to the neutral wire.
  • Always test the RCBO to confirm that it works properly.
  • Disconnect the main breaker or supply before performing any work on electricity.
  • All wiring installations should adhere to the 18th Edition BS7671 – Regulation 531.3.3.
  • Contact a licensed electrician for proper wiring installation according to local area codes.
  • The author will not be liable for any losses, injuries, or damages resulting from the display or use of this information or if you attempt any circuit in the wrong format. So, please be careful because it’s all about electricity, and electricity is too dangerous.

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