Shower tripping problem RCBO

[gazdkw82]

Honestly. I feel abit of a donut. Thinking about it, iv approached the whole thing wrong. It didn't help having the guy on my shoulder like a puppet watching my every move.

Im a little annoyed but its a lesson learnt.

Iv got a new RCBO. I better hope that it works or else the other thing it can be is the cable!

 

[hightower]

Honestly. I feel abit of a donut. Thinking about it, iv approached the whole thing wrong. It didn't help having the guy on my shoulder like a puppet watching my every move.

Im a little annoyed but its a lesson learnt.

Iv got a new RCBO. I better hope that it works or else the other thing it can be is the cable!

Just be sure to take your MFT when you go back, that way you can eliminate each aspect one at a time should you need to.

 

[gazdkw82]

New rcbo in and it trips just the same. I came to the conclusion it has to be the cable. It's the only thing left!

Did IR test on the cable from board to switch (switch in off position) 250v = >200Mohms 500v= >200Mohms

I then did IR test on the cable from switch to shower. 250v = 0.238Mohms. Aha! Found the problem. Had a look in the loft. Someone's Done a shoddy attempt at a JB. No cover, no sleeving. Bare copper everywhere. So, I replaced the cable completely from the switch to the shower. Turn power on and......trips again!

I'm baffled, go down and do another IR test from the board to the switch. 250V= >200Mohms. 500v = 0.253Mohms. Ffs. I did it 3 times and got the same readings.

I told him, it has to be your cable from the bird to the switch. He said he doesn't want to change it if it means damaging the wall

 

[davesparks]

0.253Mohms to earth gives a current less than one milliamp. Whilst this is far from an acceptable IR it is not enough to cause a healthy 30mA RCD to trip.
You also haven't mentioned what the IR test was between, I'm only assuming that test was L-E, what results did you get L-N and N-E?
Did you have the cable disconnected from the neutral bar when you tested it?

Have you looked inside the switch?

Have you fitted another 32A rcbo?

 

[gazdkw82]

Between L-N. not through the breaker. Basically took the live and neutral from the board and tested direct from there.

Looked inside what switch? Its a brand new DP switch

 

[davesparks]

Between L-N. not through the breaker. Basically took the live and neutral from the board and tested direct from there.

Looked inside what switch? Its a brand new DP switch

Did you only test from L-N? Why not L-E and N-E?
What results did you get when you tested the new rcbo?

I missed the post where you said it had been replaced, have you checked that it has been connected correctly?

 

[hightower]

L-N, my money is on your low reading being caused by a neon in the shower unit.

It seems you're looking for an earth fault mate, so why didn't you test L-E and N-E?

 

[Richard Burns]

An IR value of 0.238MΩ tells me that you are testing through a neon indicator of some sort, though the change from 250V to 500V could indicate a low level (400V) surge protection device as well this seems unlikely on a shower.
Just test (L-E, N-E possibly L-N) the cable disconnected from any accessory, but with the earth connected in the board.
From the description of the fault:
i.e. it only trips when the shower is physically moving water through the shower, but not necessarily heating the water as it happens when on cold.
And with you having no tripping when it is an MCB not an RCBO which shows it is an earth fault not a short circuit fault.
The IR results are non conclusive because of the way the test was carried out.

I would expect that there was water leaking into the shower electrics from somewhere, although changing the shower should have eliminated this but it is worth checking.

 

[gazdkw82]

the cable was disconnected from the board and the switch was in the off position. There is no way the neon could be the reason for the readings because the neon only works if the switch is in the on position. I don't know why I didn't test between L-E. don't forget guys I'm still learning. I just assumed Testing the L-N would show me the problem.

 

[Richard Burns]

238,000Ω is too low for standard cable deterioration, though possible.
it is too high for a cable physically damaged unless there were water covering the damage and causing a partial connection, it is the sort of value you get from an electronic device in circuit, actually is is about twice what I would expect for an LED "neon" and about half the value for a normal neon, but probably close to a value for a PIR sensor, none of which really helps define the problem.
One thing is to ensure you have not wired the switch load to supply and supply to load (just in case) thereby putting the neon in circuit all the time.
If you are looking for cable damage then the likely points are on exiting the CU and entering the shower area (i.e the switch or the shower itself), though of course nails through cables (that were then removed) anywhere is a possibility.
Thinking that there was a JB in the switch to shower route might there be a JB somewhere on the shower to CU route (e.g. does the cable look the same colour/type/size at the CU and the switch)?
Is the cable route identifiable to trace possible causes of damage?

 

[gazdkw82]

Can't inspect the cable physically as it's plastered into the wall. It's not a long run from the cu to shower (3 metres) iv thought about hard wiring a temp cable through the rcbo direct to the shower and trying that. If it still trips then I know it's something at the board or the breaker again. If it works I know it's the cable

 

[hightower]

the cable was disconnected from the board and the switch was in the off position. There is no way the neon could be the reason for the readings because the neon only works if the switch is in the on position.

You said you tested the cable from switch to shower. If this is the case you've either tested a neon in the pull switch or a neon in the shower itself - ~0.2MOhms is typical of a neon in the circuit.

 

[gazdkw82]

I first tested from the board to the switch with the switch in the off position. At first the results were fine. I then disconnected from the switch and tested to the shower. The cable was also disconnected from the shower, so it wasn't connected to anything at all either side. This is how I found the JB in the loft.

As it stands now the cable from the switch to shower has perfect IR results but the cable from CU to switch has very low ready at 500v