Modern Domestic Electrics Explained

Homeowners are bombarded with technical terms and jargon when it comes to home electrics. Here are some simple explanations to help you understand your system.

The Basic Home Electrical System

Here I outline the system for a simple two storey family home, with no solar panels or other generators.

Power comes into the home via the electricity meter. The Earth connection, if supplied from the energy company will also be here. Some homes have a separate Earth via an Earth Electrode (a big spike hammered into the ground)

After the meter there is the Consumer Unit (This used to be called a fuse box). The consumer unit is a bank of switches -MCB, (miniature circuit breakers), and RCDs( Residual Current Devices). The purpose of these is to switch off the circuits in the house for maintenance, or automatically if there is a fault.

From the consumer unit cables will go to the different points in the house. Usually a ring main for each floor (the sockets), a lighting circuit for each floor, a cooker circuit, and maybe a power shower circuit. There may be many other circuits, for kitchen appliances, garden lighting or any other purpose.

The sockets, lights and other accessories are the final parts of the system for the electrician.

The Consumer Unit

Why do I need a consumer unit, my fusebox works fine?
The simple answer to this is safety. The modern consumer unit has more safety measures than the old system. Wire fuses blow when too much current flows through them. (this can happen due to a faulty appliance, faulty wiring or simply plugging too much into one circuit). When this happens the fuse needs to be removed, and a new piece of fuse wire fitted.  Over the years most systems have had the incorrect fuse wire fitted at some point, or even worse another type of wire entirely. The upshot of this is that if a fault develops, the system won’t shut off when it should, which is dangerous as cables will start to heat up and can melt and cause fires.

A modern Consumer unit on the other hand has two safety measures, the MCB and RCD. First the MCB.

The MCB, or miniature circuit breaker is a switch that will automatically switch off if the current gets above a certain amount.
Safety Benefits:  I will generalise here, (there are so many variations and exceptions I’m afraid). The MCB will disconnect in less time than a piece of fuse wire. It can be re-set easily and cannot be tampered with.

The RCD. The RCD, or Residual Current Device is one of the major safety advances in modern domestic systems. The RCD will control a bank of MCBs, and switch off them all if a current inbalance is detected.

How an RCD works:
Consider the RDC as a balance. If the current going into the system (via the brown ‘Live’ cable) does not match the current coming out (via the blue ‘Neutral’ cable) it will switch the system off. The only way the current will not match is if it is leaking somewhere, through a bad cable, bad appliance etc. The RCD will switch the power off in around 15mSeconds (0.015 seconds).


The Earth, or CPC (Circuit Protective Conductor) is broadly the system of cable that connects all the accessories and metal parts of the house to the ground. The reason this is vital is that if any fault occurs power will easily flow to earth, and the system will switch the circuit off.