Lesson 5
Demystifying the Fuse Board
Read your consumer unit from the front: what the main switch, MCBs and RCDs each watch for, and what a trip is telling you.
One switch down, half the house dark
One evening the kitchen and half the downstairs lights go off together. At the consumer unit (the fuse board), one switch is down. Which one it is tells you a lot, so it’s worth knowing what each kind does.
Most modern boards have three kinds of device. A main switch turns off everything the board supplies. MCBs (miniature circuit breakers), one per circuit, watch for too much current. RCDs (residual current devices) each guard a group of circuits. Older boards may have fuses instead of MCBs, and no RCD at all.
All of this is read from the front with the cover on. The cables coming in stay live even with the main switch off, so the inside is an electrician’s. Use only the switches and test buttons on the front, as their labels say, and don’t keep resetting something that trips again: repeated trips need an electrician to find out why.