Dual RCB CU, RCB trips but MCB is not tripping.

[securespark]

I think the quickest way to narrow it down would be to disconnect every circuit you can live without in the short term.

The first four in your list are ideal candidates.

Disconnect both the line and neutral for each circuit.

Then sit back and see if the tripping stops.

Leave it as long as you can. It depends on how frequently your tripping is occurring. For example, if your RCD trips once a week, leave it a week or 10 days with the circuits disconnected.

If the tripping stops, there's a good chance the problem is on one of the disconnected circuits.

Then you reconnect them one by one.

 

[JohnW2]

If the tripping stops, there's a good chance the problem is on one of the disconnected circuits. ... Then you reconnect them one by one.

That's certainly one approach. However, as I explained in my recent post, it might be better to disconnect them one at a time, rather than disconnecting everything and then reconnecting them one at a time ...

... in the 'worst case scenario' I mentioned (tripping as a result of sub-trip leaks in two or more circuits), if you disconnect them one at a time you will hopefully discover all of the circuits which are contributing to the total leak causing the trips (since disconnecting just one of them will stop the trips). However, if one disconnects everything and then reconnects one at a time (leaving previously reconnected ones still connected), the trips will not reappear unless/until all contributing circuits had been reconnected - leaving one uncertain as to whether the problem was due solely to the last one being reconnected, or to a combination of that and one (or more) of the previously reconnected circuits. If one reconnected circuits 'individually' (i.e. only having one 'reconnected' at a time), in the scenario I'm talking about the trips would never re-appear.

Your approach would, of course, save some 'wasted time' in the event that the trips persisted even when all of the 'suspect' circuits had initially been disconnected - so there's a bit of 'swings and roundabouts'.

... just my few thoughts!

Kind Regards, John

 

[platforminc]

Thanks everyone for your useful posts.
It is highly appreciated. I will disconnect one at a time, since isolating the MCB by turning it off is no good. Is it possible to disconnect only neutral or does live needs to be done as well ? I am just trying to minimise what needs to change etc.

I have seen the CU opened before whilst works were being carried out in the house, I would isolate the power completely and work out how to open a CU and how to disconnect individual cables, I know it all hangs together using some kind of screws, you screw the cable to the corresponding terminal.

Just not paid attention to it being opened and all. But I will figure it out and report back.

Thanks once more.

 

[JohnW2]

It is highly appreciated. I will disconnect one at a time, since isolating the MCB by turning it off is no good. Is it possible to disconnect only neutral or does live needs to be done as well ? I am just trying to minimise what needs to change etc.

As you are suggesting you could switch off the MCB (to isolate the L) and then disconnect just the neutral from the neutral bar (and put the disconnected neutral into a bit of terminal block or suchlike to keep it safe). However ...

I have seen the CU opened before whilst works were being carried out in the house, I would isolate the power completely and work out how to open a CU and how to disconnect individual cables, I know it all hangs together using some kind of screws, you screw the cable to the corresponding terminal.

... are you sure that you are happy, comfortable and sufficiently competent to 'fiddle around' in a CU? Even with the CU's main switch switched off, there will be some live bits within the CU (the input side of the main switch) - unless you have an external isolator which would enable you to totally kill the supply to the CU (do you?).

Kind Regards, John

 

[platforminc]

I can manage. There is a big black fuse which is where the supply comes from. I will take that out to ensure full isolation.

 

[Taylortwocities]

I can manage. There is a big black fuse which is where the supply comes from. I will take that out to ensure full isolation.

NO NO
That big black fuse is the property of the supply company. It may not look like it but there are several dangers with pulling one of those fuses (it actually probably is sealed so you cannot remove it).

The proper way is to follow safe isolation procedures using a voltmeter (see WIKI). Turning off the switch that is marked MAIN SWITCH on your consumer unit is the way to turn off teh supply.

 

[platforminc]

I thought I read from above that turning on the main switch may not isolate everything? If I read wrong the big left red switch on the CU picture is the main switch for this CU.

Is that enough to isolate everything? Also that big black fuse is a cut out fuse.

 

[JohnW2]

NO NO...

Indeed - assuming that he's talking about the cutout fuse.

The proper way is to follow safe isolation procedures using a voltmeter (see WIKI). Turning off the switch that is marked MAIN SWITCH on your consumer unit is the way to turn off teh supply.

As I said to him, even turning off the CU's main switch will leave some 'live bits' within the CU casing. Whilst isolation by means of that main switch is fine for working on anything in the installation downstream of the CU, working in the CU (assuming there's no external isolator) requires one to be comfortable and competent enough to know how to do so safely (and even more so if it's a metal CU ) - hence the question I asked the OP.

Kind Regards, John

 

[JohnW2]

I thought I read from above that turning on the main switch may not isolate everything? If I read wrong the big left red switch on the CU picture is the main switch for this CU. Is that enough to isolate everything?

As I said to you, and have just repeated in my reply to TTC, switching that Main Switch off will isolate 'almost', but not quite, everything inside the CU case. The incoming supply to that switch will remain live, even when the switch is 'off'. If it's been wired properly it should not be too easy to touch those live bits, but one needs to be aware of the issue, and to be careful.

As TTC has said, as well as 'not being allowed', pulling the cutout fuse can also be dangerous.

Kind Regards, John

 

[John D v2.0]

There is a big black fuse which is where the supply comes from. I will take that out

this has GOT to be someone trolling?? especially since in the original phot the cutout is a modern grey one
I hope so anyway!! Who is it?

 

[platforminc]

Got it now. Will not touch cut out and would be careful even after isolating the main CU switch.

 

[JohnW2]

this has GOT to be someone trolling?? especially since in the original phot the cutout is a modern grey one

I hadn't noticed the colour issue but, in the name of 'giving the benefit of the doubt', I would not have jumped so rapidly to the same conclusion as you!

I'm actually a bit confused by that photo - there do not appear to be any tails coming out of the sealed grey thing (which looks like "a modern grey cutout").

platforminc: could we perhaps have a 'wider view' photo than the one you posted - allowing us to see more of what is going on around that area (and showing us the "big black fuse")?

Kind Regards, John

 

[platforminc]

Please see the picture.

 

[Taylortwocities]

Two fuses in that picture. One being used and one not being used. Both of the fuses are grey.
The only black thing is the (sealed) neutral connection block.

 

[platforminc]

Sorry I forgot to mention. It's grey and not black.