I have noticed quite recently that when I go to my garage where my RCD unit and electricity supply box is, I can hear a buzzing noise coming from one or other of these boxes. What does this mean? The noise comes and goes. Is it dangerous?
hi there this is not a normal thing for an rcd to be buzzing i would suggest you get an electrician to look at it sooner rather than later as it could be
loose conections and the buzzing sound is arking of the cables which could result in fire, most electricians should come out to asses the job for free so ring one soon as mate.
if you have a high inductive load for example HID, fluorescent lighting or triac dimmers that can cause the RCD to buzz. also if it has a high load on one of the MCB's they can sometimes buzz however this depends on the breaker's condition. some theater lighting dimmers and electric motors cause RCD's to buzz.
The older RCD's had larger current transformers than the new ones and no electronics these may buzz in the main it means you have some earth leakage but not enough to trip it.
The problem with RCD's is the strain the wires put on them can stop them working they are detecting very small amounts of current. So after one is fitted one uses a special meter to check both trip currents and times. 40 mS is too short of a time for a stop watch it needs special meters to measure it.
So changing a RCD is something you need an electrician for as the meters are just too expensive to be worth doing DIY.
So yes it's an electricians job no real way around it.