Circuit breaker problem

[DIYlevel1]

Hi all,


I'm looking for some help with an issue in my consumer unit (photo attached).


The second MCB from the left has tripped. (I cant really read it.)


The problem I'm having is that whenever I try to reset this specific MCB by flipping it up, the main RCD switch immediately trips and cuts power to that entire bank of circuits.


I would be grateful for any advice on the following:

1. What is the likely fault when resetting an MCB causes the RCD to trip instantly
2. Are there any simple and safe diagnostic steps I can take myself before calling in an electrician?

Thank you for your time and any help you can offer.

 

[Wayners]

Unplug everything.
With fused spurs in the kitchen or anywhere pull the fuse draw out.
Then try flipping switch.

Then one by one turn things back on

 

[Rodders53]

I read IMMersion 1 on LH RCD and IMMersion 2 or RH RCD

So find the HW tank and post a pic of tank wiring / switches / any labelling.

Immersion heaters often fail with a short between the heating filament and the earthed outer jacket. The faulty one will need replacing (that'll be fun, not).

1 may be the top 'boost' immersion and 2 the lower 'full tank' one --- or vice versa.

MCB labelled TR WC is probably the electric towel radiator in the toilet?

I note that the Central Heating is a 40A mcb so that is a beefy electric heater system (wet?).

 

[securespark]

Rodders' interpretation of the scribble on the CU is spot on.

The fact that the RCD trips as soon as you energised the MCB seems to suggest that there is a live/ earth fault on that circuit, most likely as Rodders describes.

The immersion element could do with testing to see what the readings are between L and E and N and E.

Ideally you'd use an insulation resistance tester, but you could in this case if you're handy, use a multimeter set to continuity.

If not, call a spark, but if it does turn out to be the element, not many electricians will tackle changing them.

 

[plugwash]

not many electricians will tackle changing them.

AIUI the problem with immersions is you have a very large screw thread in a relatively thin tank with the result that sometimes attempting to unscrew the immersion can tear the tank, at which point you have a large emergency plumbing problem on your hands.

 

[Murdochcat]

Do you really have 2 x immersion heaters? If so go to the airing cupboard and switch BOTH off at their isolation switches.

Then try and reset the MCB - if the RCD stays on, then turn the immersion heaters back on 1 by 1 and see what happens.

If the RCD trips when one of the Immersion heaters is switched back on, can you cope just using the 2nd immersion?

A photo of the airing cupboard / hot tank / isolation switches / timers may be helpful

 

[Harry Bloomfield]

AIUI the problem with immersions is you have a very large screw thread in a relatively thin tank with the result that sometimes attempting to unscrew the immersion can tear the tank, at which point you have a large emergency plumbing problem on your hands.

There was a thread, where a solution was found, to remove a seized immersion element, without wrecking the cylinder. Basically - drill holes through the element brass boss, to allow a jigsaw to be used, to cut out a triangle of the boss, from the middle, out to the thread - making it possible to tear out a section of thread. The boss, should then unscrew easily, without any damage to the cylinder.