RCCB trips when Shower turned off

[Daddy Boots]

Had a split load cu fitted last year and had the sparky connect my 9.5Kw shower to a 40A mcb protected along with the ring circuits by a Siemens 80A RCCB. The 10mm cable run is about 9m...totally free the whole run as I've not decorated the middle floor room it runs through. A few months ago I got occasional nuisance tripping of the RCCB when the isolator switch was turned off after the kids had showered. Things have worsened and I now get RCCB tripping maybe one time in four when the shower itself is turned off. I've tightened all of the connection in the circuit though none were loose, and there's no moisture inside the unit. Any ideas ?? Last time it tripped noticed there was some condensation on the tiled walls/outside of the isolator switch which is in the corner of the bathroom.....it's a sloping roof in the bathroom at the top of the house and not particularly warm at 0700 in the morning...... I can't convince the kids to open the Velux and leave the door open. I can get access to a mega/eath leakage tester.

 

[Adam_151]

Firstly, just checking are you turning the shower off by the isolator switch, instead of on the unit? you are not supposed to opperatate the isolator switch under load, its not designed for that, though feel free to operature the isolator switch when the shower unit itself is switched off, not really much to do with the problem, but I thought I'd meantion it anyway.

RCDs tripping when something is turned off is usually something to do with neutral being broken before live, check the continutity is correct at all points in the circuit, it could be the isolator switch has gone a bit faulty and is breaking neutral a bit before live

 

[JohnD]

on an entirely different tack, if you can put in an extractor fan coupled to the light, it will cut down the coindensation surprisingly well.

 

[Daddy Boots]

The RCCB trips when the shower unit is switched off, not when the isolator is switched off. The circuit is cu to isolator in one 9m run and 1.5m run from isolator to shower unit and all 3 sets of connections have been physically checked and tightened.
As I did have very occasional ( 1 in 20) RCCB trips in the early days when switching off the isolator ( having already turned off the shower unit) and now I have frequent ( 1 in 4) trips when the shower unit is turned off I'm beginning to suspect the RCCB.
If I call stall she-who-must-be I'll see what happens when the weather gets warmer and there's less condensation ( not that there's a great amount anyway....what would you expect from 9.5Kw), otherwise I may be in for an RCCB change. There's nothing else in use that is loading the RCCB at 0700....the fridge and freezer have had their doors closed all night so they won't be running, there'll be a couple of radios and the c/heating pump.
PS I did get 3 quotes for the cu install... two very similar and one twice the amount....ex SWEB who talked about circuit testing, presumably with a mega. If he hadn't been smoking a spliff before he arrived I might have given his quote more consideration.

 

[Steve]

otherwise I may be in for an RCCB change. There's nothing else in use that is loading the RCCB at 0700....the fridge and freezer have had their doors closed all night so they won't be running, there'll be a couple of radios and the c/heating pump.

1. fridge freezers dont retain their "coldness" indefinitely. They will probably cycle 4-5 times in a night, therefore may well be running when you take a shower first thing.
2. central heating pumps (and any other motor, including the fridge compressor) are prone to getting small earth faults which will occasionally trip an RCD.