How do I read my consumer unit?

Locally it is called an elektro tabla, and in older buildings you will find it by the front door or on the landing next to the meter.

What is in it

The main switch disconnects everything. It is first on the left and usually the largest device.

The RCD is two modules wide and has a button marked T. It reacts to current leaking to earth.

The breakers come one per circuit. Each is marked with a number and a letter, for example B16.

Surge protection, if fitted, normally sits next to the main switch.

How to read it

Work left to right: supply, main switch, RCD, then the circuits. The number on a breaker is its current in amps: 10 for lighting, 16 for sockets, 20 or 25 for a water heater or air conditioner. The letter says how quickly it trips on a sudden surge.

The breaker size follows the cable cross-section behind it, which is why a larger one is never simply swapped in.

Why labelling is not cosmetic

At two in the morning, with water coming through a ceiling, the difference between a labelled board and an unlabelled one is whether you switch off one circuit or the whole flat.

The same applies to anyone who works on the installation after you. Every circuit gets a permanent label during a consumer unit upgrade, written to still be legible in ten years rather than in marker pen on the door.

What an old board looks like

Ceramic screw-in fuses and no RCD at all, which was the standard in buildings up to the eighties. Circuits added over the years without the board ever being reworked, so lighting and sockets share protection. Nothing labelled, so finding the right circuit is done by trial.

None of that is dangerous by itself, and all of it becomes expensive the first time a fault has to be traced. That is usually where fault diagnostics starts, and what drives the cost of a replacement is set out in what a new board costs.