Shower tripping RCD

[jimafblack]

Hopefully someone can point me in the right direction.

I have had an ongoing problem with an electric shower and in particular the double pole isolating switch. Ever since the shower was replaced several years ago with a Triton Millenium shower, the switch periodically has failed.

When I have repalced it the switch looks like it has overheated and always on the neutral side. The cable insulation was also discolured.
I guess I probably investigated this further but nipping off to Screwfix for a new switch evry so often seemed simpler. I should also add that we are now on our second millenium shower as the first one failed after four years so I don't think the shower is the root cause of the switches failing?

On boxing day, the main RCD kept tripping whenever the switch to the shower was activated.

I assumed it was the switch again, and to confrim this I disconnected the cable at the shower terminal block. I assumed that if there was no load then the fault was likely to be related to the switch.

I replaced the switch today and the main RCD is still tripping whenever the shower switch is activated.

So....

If the cable to the shower is disconnected at the shower end and the RCD still trips when the switch is activated, does that indicate that there's a fault in the wiring or have am I misunderstanding how the RCD operates.

One thing I should mention is that the cable run from the main board is very long as its a old house and the shower is on the top floor with the board is on the bottom floor.

Hope someone is able to give me a few clues

rgds

Jim

 

[Spark123]

An RCD detects an imballance of current between L&N, usually caused by current travelling along the earth wire or through a person etc to the general mass of earth.

My immediate thoughts are you should have stripped the cable back a bit to a point where it isn't damaged. Replacing and replacing switches isn't good, it indicates an underlying problem. What size switch is it (A), what size shower (Kw) and what size cable?

It may not even be the shower circut at fault causing the RCD to trip, with one type of supply it is possible that a fault on one circuit will trip an RCD when a heavy load is applied on another circuit.
Even saying that, get the shower switch fixed pronto!

 

[londonboy]

When you replaced these switches did you make sure you cut back damaged/burnt copper?

Do you know if the cable is the correct size for the shower?

Yes your right, if you disconnected the shower (at the unit) and the RCD still tripped the fault would be within the fixed wiring.

Although I would have expected the shower to be at fault.

 

[jimafblack]

I cut the cable back yesterday by about six inches on the supply and the load side and the fault "dissapeared".

But this morning the same again - the RCD trips as soon as the pull switch is activated. I've tried this with all the other circuits on the consumer unit switched off but still the same. I've not managed to disconnect the supply at the shower yet, but I assuming the RCD will still trip as it did the last time I tried this.

If I can eliminate it down to one of the fixed cables, is there a way to test the cable at all? Based on the replies and if I understand them I would be looking for a open circuit on the live or neutral wire rather than a short circuit?

This is getting serious now, my three daughters are all home from uni, and the day is gone before I can even get into the bathroom! Help!!!!

Jim

 

[ColJack]

I can almost garuntee that you have a N-E short in the cable from the switch to the shower..

take out the load side cables from the switch and see it it still trips when switched on..

there will be a nail or screw through the cable somewhere, or given that it was intermittent, it could be a heating pipe under a floorboard somewhere.

 

[electronicsuk]

Really we could do with knowing the size of cable before going any further. If it's undersized, continuous overload over the years could have caused damage further back that you can't see.