by ericmark »
Sun Dec 06, 2020 12:37 pm
I can't see any way working on the immersion heater can cause any damage to an oven.
I can see how to avoid turning whole power off, an electrician will try to work switching only the line supply to the items being worked on, and while working on them earth to neutral could trip a general RCD.
I also know that RCD's can get stuck, there is normally a notice on them to say test every month or other period to ensure they have not stuck, and that if it had stuck, being operated a few times will likely have freed it off, so now working as it should.
Tripping the power will stop an oven working, as the clock will need resetting, however it should not cause any damage.
Homes can have 1, 2, or many RCD's, in the main with only one either it is 100 mA or only covers sockets if 30 mA, with two the idea is in any room sockets and lights are not on the same RCD, so if there is a fault which could cause a shock, you don't also get plunged into darkness, however lights are traditionally split upper and lower, where sockets in order not to need extension leads up/down stairs are split side to side, so often with just two RCD's it is impossible to split so lights and sockets are not on the same RCD in all rooms.
So the better idea is to use RCBO's which are RCD and MCB combined, but they cost more, so many homes still have only 2 RCD's my home has 14 RCBO's fitted.
One can hardly blame the electricians if to save money only one or two RCD's have been fitted and you wanted power while he was working so in spite of the danger to him, he has worked live (neutral is considered as a live wire) to allow you to continue to have power, technically he should isolate and you can't fully isolate with an MCB, so either he should have turned off the RCD or isolator before working, we often do take a chance and only turn off the line, and not turning off neutral was no danger to you only him. He is permitted not to turn off neutral with a home on a TN supply, but as you found out, neutral - earth faults can cause the RCD to trip.