Why is my fuse box (consumer unit) buzzing?

Why your fuse box is buzzing

The answer is almost always the same: something is vibrating or heating up. A fuse board (consumer unit, or breaker panel in the US) in good condition is practically silent, so it is worth knowing what kind of noise you hear before deciding how urgent it is. In Spain it is called the cuadro eléctrico.

The usual noises and what they mean

• A soft, steady hum. Some devices with a coil make it: contactors (the ones that switch the water heater or a timed circuit), lighting relays or doorbell transformers. If it has always sounded the same, it may be normal.
• A hum that grows or changes with use. Usually a loose connection: a badly tightened cable in a terminal vibrates and heats up when a lot of current flows, for example with the oven or the air conditioning on.
• Crackling or sizzling. There is an arc in a connection. It is dangerous: the terminal is slowly burning.
• Repeated clicking. A contactor or relay switching in and out, or a breaker at its limit.

Signs it is urgent

• A smell of hot plastic or burning.
• Black marks, melted plastic or a breaker that is hot to the touch.
• Lights flickering at the same time as the noise.
• A breaker that trips on its own and starts buzzing again when reset.

In any of these cases, switch off the main switch if you can do so safely, and do not open the board.

How it is diagnosed

The electrician checks the board with power on and off: tightens the terminals, tests the breakers and RCDs and, if needed, uses a thermal imaging camera to see which connection is hotter than the rest before it fails. If the board is old or has burnt components, the sensible option may be to replace it.

What it costs

When to call an electrician

Call if the noise is new, if it is getting louder or if it comes with heat or a smell. In Seville, Spain, our 24-hour emergency electrician handles fuse box faults, we advise on fuse board replacement and we carry out thermal imaging of boards and installations.