New single RCD consumer unit

[AndyPRK]

So the kitchen MCB is tripping too?

And the rcd on the far right ?

Do they both trip together then?
Then you can reset the rcd.

 

[flameport]

Once the MCB is back on it stays on until tripped later during a shower.(maybe days later)
Is it possible that a shower cable that runs in close contact with other cables could cause and induction loop?. But I thought this would quickly dissipate. The cables are all together for 1.8 m after leaving the rcd.

Adjacent cables will not cause such problems.

The options for one circuit to trip another are :
some bizarre interconnection between the circuits - however if it has all been tested this would seem very unlikely, and even if there was such a fault it should cause problems all the time, not intermittently.

overheating, usually two or more heavily loaded adjacent MCBs in the consumer unit - however this on it's own would not cause an RCD to trip.

water leakage, such as when persons use the shower either correctly or incorrectly, water is leaking into some socket, junction box, damaged section of cable or whatever, causing a fault and taking an hour or so to dry out. This could easily trip the MCB for the circuit and the main RCD as well.

 

[JohnW2]

The options for one circuit to trip another are :
(1)...some bizarre interconnection between the circuits
(2)...overheating ..... however this on it's own would not cause an RCD to trip.
(3)...water leakage ....

... OR (4), as bernard has pointed out, a N-E fault (of non-negligible impedance) on any circuit can result in an RCD tripping when some other circuit (protected by the same RCD) draws a substantial current. As he said, this is most likely with a high-current circuit (like a shower or cooker) (but perhaps not with lower-current circuits) and will happen in response to that high current load being switched on, even though the N-E fault is on some other circuit. If the N-E leakage current were fairly marginal, the phenomenon could appear to be intermittent.

Kind Regards, John

 

[RF Lighting]

A quid says it's water ingress.

I'm sure a competent electrician with an IR tester would confirm this pretty quickly

 

[flameport]

... OR (4), as bernard has pointed out, a N-E fault (of non-negligible impedance) on any circuit can result in an RCD tripping when some other circuit (protected by the same RCD) draws a substantial current.

True, but in this case there is an MCB tripping as well - not something which an N-E fault could cause.

 

[JohnW2]

A quid says it's water ingress.

On of the very first things taught to me during my higher education (and then repeatedly drummed into me thereafter) was that "common things are common" (too-clever-for-their-own-good students have a habit of concentrating on the esoteric and very uncommon) - so, on that basis, I would not bet against you

Kind Regards, John

 

[JohnW2]

True, but in this case there is an MCB tripping as well - not something which an N-E fault could cause.

True - but I have to say that I'm getting a bit confused by this MCB tripping. We seem to be being told that the RCD trips when the shower is being used, but that the RCD cannot be reset if the kitchen sockets MCB is reset - so when does the kitchen sockets MCB itself trip - simultaneously with the RCD, or when (and, of course, why!)?

The shower and kitchen sockets MCBs are adjacent in the CU - so I suppose it's possible that an over-heating shower MCB is causing an adjacent on-its-last-legs kitchen sockets MCB to operate - but that would explain neither the RCD trip nor the fact that the RCD will not reset if the sockets MCB is reset!

Kind Regards, John

 

[nairb123]

A quid says it's water ingress.

I'm sure a competent electrician with an IR tester would confirm this pretty quickly

It was the very first thing I checked. Resealed around bath. New shower unit installed by same electricians. They had the "tails" out of rcd and re-tested them (not sure what the test was). They reported the system stable.
I have run the shower many times in one day - no trip. Had 2 of the tenants have a shower..... All OK. 2 days later it trips 3 times in 2 days. Then goes ok for a few days.

I may have concentrated on the shower end to much.... I need to check right back to water source in loft. There is more checking to be done to really be sure that water is not the issue.

There was only a visual inspection prior to installing the new equipment. No mention of single/dual rcd.

I really appreciate the input into this issue. I could go and spend the 500 quid on a new dual rcd... or have the shower re-wired.. or even more on a new kitchen circuit. But I could do 2 of those things and miss the fault competely

 

[AndyPRK]

Please explain, does the kitchen MCB trip?

If it got to it you would be better off with all rcbos than dual RCD.

 

[JohnW2]

I really appreciate the input into this issue. I could go and spend the 500 quid on a new dual rcd... or have the shower re-wired.. or even more on a new kitchen circuit. But I could do 2 of those things and miss the fault competely

Indeed - that's the point. There are really two totally different issues being discussed here. Firstly, there's the matter whether you should have a dual-RCD CU. However, even if you had one installed, that would quite possibly/probably not sort out the tripping problems (although it might make subsequent trouble-shooting a little easier). The tripping issue, which seems complicated/mysterious, is a totally separate issue - which I feel sure is what you should first be concentrating on.

Can you help me with my confusion regarding the (kitchen sockets) MCB tripping - when exactly does that happen? ... at the same time as the RCD (whilst shower is being used), or when?

Kind Regards, John

 

[nairb123]

Please explain, does the kitchen MCB trip?

If it got to it you would be better off with all rcbos than dual RCD.

Now at this point I only have the tenants word. I know the RCD trips because all power goes. I believe when she tries to turn the switch back on it fails. She follows the instructions in the pamphlet for the CU and switches all the MCBs off. The switches them on one by one until one causes the RCD to trip again. She now knows that its the second kitchen ring MCB that must be left off. When left off the system seems to be fine. To start with she left the kitchen ring off for a week. She has found that she can switch the mcb on again after a short time (2hrs). The shower MCB seems to be ok. I believe she has unplugged all equipment and tried to switch the mcb back on and it failed. We have also tried running all equipment at once on the kitchen ring and it seemed ok. This fault just does not happen to order....

But I am learning about RCB/MCB/RCBO very quickly. Its interesting.... wish it was in my house and not in a tenants house with a busy mother of 2

It does seem like water ingress.......

 

[JohnW2]

I know the RCD trips because all power goes. I believe when she tries to turn the switch back on it fails. She follows the instructions in the pamphlet for the CU and switches all the MCBs off. The switches them on one by one until one causes the RCD to trip again.

Ah - so, as far as you know, that MCB does not actually trip on it's own?

Kind Regards, John

 

[nairb123]

There are really two totally different issues being discussed here. Firstly, there's the matter whether you should have a dual-RCD CU. However, even if you had one installed, that would quite possibly/probably not sort out the tripping problems (although it might make subsequent trouble-shooting a little easier).

Yes .... there are a number of inputs into this from different places. An electrician "up the road" from the tenant says the rcb is too sensitive. I should use a 100a 100ma. ?? is 30ma to 100ma really going to solve the problem?.

But I agree that changing the rcd might just mask the problem. I know a lot about computer software systems but nowt about RCDs. Or fault finding on them.
Logic says water. But non found so far yet. A dual rcd would help find it tho

 

[nairb123]

I know the RCD trips because all power goes. I believe when she tries to turn the switch back on it fails. She follows the instructions in the pamphlet for the CU and switches all the MCBs off. The switches them on one by one until one causes the RCD to trip again.

Ah - so, as far as you know, that MCB does not actually trip on it's own?

Kind Regards, John

I will confirm that with the tenant. I know it needs to be left off to get up and running again. Hence the thinking that the two are in someway connected.
I have actually seen the switch off when I visited(often at the moment)

 

[JohnW2]

An electrician "up the road" from the tenant says the rcb is too sensitive. I should use a 100a 100ma. ?? is 30ma to 100ma really going to solve the problem?.

If the 'leakage' causing the RCD to trip were fairly marginal (between 30mA and 100mA) then changing to a 100mA one might well 'cure' the problem. However, it would be totally contrary to the regulations and would leave people exposed to a theoretical risk of death - the whole point of having 30mA RCDs is that 30mA is the magnitude of electric shock above which death becomes an increasingly serious possibility!

Kind Regards, John