Electric Shower & Central Heating on Same Circuit - RCD Switch Tripping

Demosthenes

So the RCD switch on my fusebox trips every 4-5 days on average. Sometimes twice in one day, sometimes not again for 2 weeks. I am trying to get to the bottom of what is causing it and I'm thinking it might be due to the electric shower and central heating sharing the same MCB B20 switch. Am I correct in saying this is underrated for an electric shower on its own, never mind with the CH as well?

Would this trip the RCD switch or should it be tripping the MCB switch? The MCB one never trips, but when I flip it the fusebox starts humming, which none of the other switches do.

Note I don'tknow a whole lot about this, terms could be wrong, I'm just referring to what is written on the switches themselves.

kirk.

Is it a power shower, what's the model

A power shower and CH on same mcb wouldn't be related to your issue

The fault could be anything connected to the RCD

Demosthenes

No, electric shower - a Triton T90si. Looking online it seems the T90si is an 8.5kw unit, which would need a 40amp MCB. The existing one is an MCB20, which I assume means it's 20amps?

Would the electric shower intermittently overload the MCB and then flip the RCD?

kirk.

https://www.boards.ie/discussion/comment/121279600#Comment_121279600

No it would trip MCB on overload

Post up a close up pic of board

You'll need a REC to investigate fault and shower wiring

meercat

https://www.boards.ie/discussion/comment/121279600#Comment_121279600

A t90 should be on a 40a rcbo

a rec really needs to look at this. Do not use your shower until then.

kirk.

Post up a pic of board anyhow you could be mistaken

If it's on a B20 ya the rest of its probably not safe

meercat

Also does your rcd trip even when your shower is not being used

Demosthenes

I've been reading through this old thread https://www.boards.ie/discussion/2057559329/electric-shower-fault/p1 which seems to suggest it is likely either a failing element in the shower (which should trip the switch while showering, which does not happen) or the RCBO is undersized (I don't have an RCBO but I do likely have an undersized RCD doing the same job if I'm not mistaken?) Granted there also is a level of disagreement in that thread from multiple people who seem to know what they are talking about.

RCD that trips is top left, MCB with the CH and electric shower is the 4th MCB in from top left.

kirk.

You've a B40 there and a contactor

Have you 2 electric showers or maybe that's for something else

Demosthenes

Yes 2 electric showers - never used together. Just checked and the isolater switch on the wall was off for the 2nd one when the RCD tripped - does this rule that out as an issue? That 2nd electric shower is connected to the top right B40, also a Triton T90si, while the first electric shower is connected to the B20 beside it, which I reckon is the problem one.

kirk.

What's the contactor top right for looks like you've half a priority board , no sensing relay😁

Is that the entire board in the pic

Call a Rec and as meercat said don't use showers

Demosthenes

Yes both showers are off when I flip the B40. The priority board only allows one electric shower to power at any one time if Google is correct - so should the 1st electric shower be connected to this and the B20 beside it as well, which seems to be the case?

kirk.

https://www.boards.ie/discussion/comment/121279867#Comment_121279867

You've no sensing relay in board and you said one shower is on the B20

Looks like there's some bodge job at the board

Switch off showers and call a Rec

Demosthenes

Sorry replies seem to be bugging out for me and some comments only just appearing.

Just to fill in the gaps, RCD has never tripped while the shower is running, only at random times and always when we are out of the house so far. Entire board is in the photo.

We recently bought the house, it was a one-off self build and the only previous owner did a lot of the work himself- have found other issues throughout the house.

I rang a Rec last week, he recommended seeing could I narrow things down a bit from "RCD switch keeps tripping" before he called out as it could be a long day of trying to figure it out otherwise. It sounds like there's a few glaringly obvious issues so I think that's it narrowed down enough 😅

Thanks both for your help, very much appreciated.

kirk.

https://www.boards.ie/discussion/comment/121280057#Comment_121280057

..

meercat

Your rcd tripping may be a separate issue

your showers are definitely wired incorrectly though

an insulation resistance test by a competent rec should identify the faulty circuit reasonably quick

Demosthenes

Just as a minor update on this, electrician has stated this is a slightly older setup, where the B20 is operating the switch and the B40 is operating the showers. Only one shower gets power at any one time. Switch off the B40 and neither work, switch off the B20 and only the last used shower works. If one shower is on the other can't get power. From googling it would seem to be a non-priority switch, although he didn't specifically refer to it as one.

Search for the RCD offender continues. I replaced a recently discovered faulty wired heated/back-lit mirror in the bathroom a few days back and still no luck.

Next target is the microwave/convection grill that also came with the house. It stops every 59 seconds and being too busy to investigate, we figured we were just using it wrong. Turns out the 59 second stop is essentially an error message for damper-related component failure, so that is currently unplugged and waiting to see does the RCD trip again.

kirk.

There'd have to be a sensing relay at a minimum for priority control

It's not in the picture anyhow

Demosthenes

https://www.boards.ie/discussion/comment/121319133#Comment_121319133

Think I might have solved that. The control is done manually by the switch on the wall beside each of the showers. Power on with the wall switch at one shower cuts power at the opposite shower and vice versa. When you power on one of them you can hear a 'thunk' noise from the fusebox which I assume is it connecting the requested circuit and disconnecting the opposite one.

So with one shower circuit always disconnected by the wall switches, there is no need for a sensing relay at all I think?

kirk.

https://www.boards.ie/discussion/comment/121319271#Comment_121319271

There's probably a sensing relay or board somewhere if it's automated

Hard to make sense of this setup

kirk.

https://www.boards.ie/discussion/comment/121319271#Comment_121319271

I get that now

Shower isolator energizes contactor breaking supply to 2nd shower

You'd only have priority with one contactor , wouldn't operate ' vice versa'

kirk.

https://www.boards.ie/discussion/comment/121319271#Comment_121319271

Your RCD issue is probably separate anyhow

Are you sure you're not a spark you're fairly well clued in 😁

Pod123

Sorry to jump on thread but the attached keeps tripping, for instance last night it tripped at 8 and at 12 it tripped,I reset it and tripped this morning at 7 o clock,never trips when pushed back up,no new appliance in the house ,outdoor sockets are switched off,any one able to tell what it might be,thanks.

16999738532687706543885183363299.jpg

It's the one left of the picture with the yellow button

10-10-20

https://www.boards.ie/discussion/comment/121367590#Comment_121367590

Hi, when you say "outdoor sockets are switched off," do you mean that the sockets are switched off at the plug socket or do you have an isolation switch in doors which you are referring to?

That device in the photo is an RCD (with damaged markings) so the issue here is a current leakage from live to earth - that can be caused by a faulty device or water ingress into a socket, cable device, etc. Best start by answering my first question as the majority of these RCD issues are rain/damp related.

Pod123

Turned off by a switch in the house

16999757129731625303366214347706.jpg

This switches off all sockets outside.

kirk.

Those are not exact times are they ?

Sounds like some type of nuisance trip or similar

meercat

https://www.boards.ie/discussion/comment/121367590#Comment_121367590

Check that your immersion is turned off

kirk.

Doesn't sound like an immersion unless it's going on at those times , they'd usually be an instantaneously trip

Pod123

No there not the exact times as I was trying to remember them but would be pretty close

We never turn on the immersion, all hot water is heated by oil boiler.

It's just frustrating as it doesn't trip when pushed back up

Thanks for all replies I will keep ye posted.

meercat

https://www.boards.ie/discussion/comment/121368046#Comment_121368046

Not always.

meercat

https://www.boards.ie/discussion/comment/121368197#Comment_121368197

Check that it hasn’t been turned on inadvertently