Why does my garage consumer unit buzz when the kettle is on?

Question

I fancied a cup of tea while working in the garage and didn’t want to keep going back into the house so I fetched the kettle etc and plugged it into the garage.

When I turn the kettle on, the consumer unit buzzes.

It’s a 13 amp plug and on a 32 amp circuit and it’s does it even when the kettle is the only thing plugged in so I don’t think it’s an overload issue. Also I’ve used power tools on the same plug without issue.

There’s only one socket and some lights going into the unit, the socket is on a separate mcb to the lights.

I don’t think it’s the kettle as it’s fine when used in the house.

Any thoughts on why it buzzes and what can be done?

Answer 1

Buzzing is a clue that there is a bad connection. This could be a bad breaker contact. On this side of the pond I have had top name brand breakers do this. My solution at least short term is turn that breaker on and off 10+ times with nothing plugged in. This seats the hammers in the breaker displacing the crud that was causing the problem. If the buzzing quits that solved the problem for now. I say solved the problem for now because if the arcing was severe it may return when this circuit is heavily loaded and then it's time to replace the breaker. It could be a loose wire lug also but I have found the breaker to be the cause most often even in large 3 phase systems the on off seats the hammers and things may be normal.

Answer 2

The root cause of the buzz is "EMFs" or Electro-Magnetic Fields. When current flows through a wire, it creates a magnetic field around it. When it's Edison's Direct Current, like on your car's wiring or the Tube's third rail, the magnetic field does not change. When it's Tesla's Alternating Current, like mains wiring, the magnetic field reverses in the UK 100 times a second (50 cycles/sec). This ever-changing magnetic field is what makes transformers work, which makes power to your house a possibility.

The magnetic field is proportional to current.

There is a rule that currents should be equal in all cables or conduits. This is because current travels in loops, and the current to your hob and the current returning are equal. The two wires' current, traveling in opposite directions, are equal and opposite. Held close together, they substantially cancel each other out. That prevents cable vibration in the walls.

However, inside junctions the wires separate somewhat. The it is possible for the wires to extend their magnetic field. The magnetic field can make the wire "buzz". this can damage the wire, so it's worth looking into. Much more importantly, it can expose a loose connection which can cause arcing, and wire or breaker damage.

Circuit breakers also use the magnetic fields. Power goes only one way through them (neutrals don't have breakers) so it is not canceled out. Also, breakers use a coil to intentionally amplify the magnetic field - this is how it trips the breaker on overload.

So there are several bits in there that can make noise in response to higher currents on a wire. If it's the breaker itself, that might be harmless -- but I would not tolerate it in any case, because it could mask other, dangerous sources of noise.