Circuit Protection – Understanding How To Protect Your Domestic Wiring

What Provides Your Fault Protection?

There are a few different components that go into a Consumer Unit, below are descriptions for them and what they are used for. Call our electrician Brisbane 24 hours faulty air conditioning and hot water system damage


An MCB, or Miniature Circuit Breaker is the modern equivalent of a fuse, with the added ability to be reset rather than needing to be replaced. Their design means they trip when the circuit they are attached to draws more current than they are rated for. This can be caused by a circuit being overloaded or by a short circuit. Typical ratings are 6, 10, 16, 20, 32, 40 and 50 amps.


An RCD, or Residual Current Device is a module that monitors earth leakage by comparing the electrical current going in and out of a circuit. If it detects a difference in the incoming and outgoing current, it will trip to protect against electric shock. This can take out an entire board, or just a bank of MCBs, depending on what it is attached to. If your lights are on the same bank as something that has tripped, your lights will also stop working. This is called nuisance tripping.


RCBO stands for Residual Current Breaker with Overload protection. It is basically a combination of an MCB and an RCD in one unit, providing the single circuit overload protection of an MCB, with the earth leakage detection of an RCD. This makes them the most flexible and versatile solution for circuit protection. Although they do cost more to buy, they completely eliminate nuisance tripping.

Mains Switch

A mains switch is the final shut off point for all the circuits in your consumer unit. Manually operated, it completely isolates all circuits on a board. Most commonly double pole, but sometimes triple pole depending on how large an install it is controlling. 100 amps mains switches are usually used in domestic circuit protection, meaning no more than 100a can be drawn by all circuits on that consumer unit.

Din Rail

This is the bar that all protection devices are attached to, to hold them in place.

Bus Bar

The Bus Bar is a copper toothed plate that connects all protection devices together electrically.

Neutral Bar

This is the terminal bar that accepts all the neutral connections for all circuit protection devices.

17th Edition Regulations

To comply with the 17th edition of the wiring regulations means that all circuits must be protected against earth leakage to prevent electric shock. In its most basic sense, this means that all circuits must be attached to an RCD or RCBO. There is however, a little more to it than that. Of the four kinds of boards available; Mains Switch, Split Load, High Integrity and Dual RCD, all can be configured to be compliant with the 17th edition of the regulations depending on the variables of the individual installation. Total current draw and number of circuits must be considered, with provision for specialist circuits.

The best way to fully meet the regulations is to have a High Integrity, or fully configurable board, with a mains switch and two RCDs. This, by way of three neutral bars, allows separation of circuits on two RCDs, your fridge, cooker, ring mains for power sockets etc, while also having RCBOs for things that must not be switched off, like smoke alarms, security alarms, or lighting for safety.

The most complete way to achieve total separation of circuits it to use a mains switch board entirely populated with RCBOs, giving overload protection and earth leakage detection on every circuit. This however, is not the most cost effective installation, but gives the most comprehensive system available.

How to Populate a Fuse Board

The most effective way to populate a High Integrity board is, from right to left, as follows:-

Mains switch: Final and complete isolation of power to board.

RCBOs: Depending on the size of your board, one to three for specialist circuits. Fire alarms, security alarms, possibly some lighting for visibility at night if a trip occurs.

RCD: Monitors earth leakage on first bank of MCBs. These must not draw more current than the RCD is rated for.

First bank of MCBs: Circuits for fridge, ring main for kitchen power sockets. Ring main for remaining downstairs power sockets. Downstairs lighting.

RCD: Monitors earth leakage on second bank of MCBs. These must not draw more current than the RCD is rated for.

Second bank of MCBs: Circuits for cooker, ring main for upstairs power sockets, upstairs lighting, shower.

These suggestions are entirely for example. The requirements of every installation will be different and circuits will be placed in different banks for different reasons. Consult your electrician for the correct requirements of your installation.

Amendment 3

From January 2016, amendment 3 of the 17th edition wiring regulations comes into force in the UK. Amendment 3 states that all domestic consumer units and similar switch gear must have their enclosures manufactured from non-combustible material, ie metal or other intumescent material. This is to ensure that he unit is able to contain any fire resulting from an electrical fault. The unit must therefore have the main body, cover for the breakers and cable entry points made from fire retardant material in order to comply with Amendment 3. These changes do not impact existing installations so there is no need to replace your existing unit, it is only for fuse boards fitted after January the 1st 2016.

In conclusion, the domestic consumer unit and its related parts is something that can be understood in principal by anyone who owns a home and wants to know how to protect their domestic wiring. However it must be said that the voltages involved can easily kill, so installing, changing or refreshing anything to do with your consumer unit must only be carried out by a qualified electrician who is experienced and trained to undertake the work safely. Click here to qualified electrician.

Julian M Jones writes for Consumer Unit World. For more information on UK fuse boards and Amendment 3 compliant products, visit

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