RCD tripping - why?

[mike-evans]

Hi all. Over the weekend I've had a strange electrical fault bugging me..

The washing Machine is tripping out the RCD, no other breakers..also the oven does the same, trips RCD but no other breaker???

Me and my father in law (he's a qualified Elecy) done a little digging on it last night, disconnected the Heating element in the WM and run it, and it run fine (seems ok as it's not heating the element)...
Then I turned the oven on (with WM running with Element disconnected) and it tripped the RCD...

If I unplug the WM and turn on the oven, it will trip..
If I turn the WM on and let it run for a minute or so, it's fine until it starts to warm the Heating element..

I find it a massive coincidence that both appliances that have independant circuits both have faults?

I'm thinking the RCD is at fault, as it protecst both of the circuits?

Can anyone shed some light on this?

House electrics are just over 5 years old, with no issues at all until now..

 

[kung]

Heard any knawing ? is the oven on a plugtop ? is it a split load twin rcd ? if so try swopping the socket circuit or oven circuit with comp ie 32a mcb on the other rcd and see if that holds ! if not see if F.I.L can get another RCD !
Best of luck buddy !

 

[kung]

You could have as said an over sensitive RCD that is caused by a wack from a faulty WM or Cooker etc etc. Dont get me wrong when i say this but is your F.I.L a qualified spark ? or a D.I ? or calls himself a spark because theres no law against saying your a spark if your not (alot of people have been had by diyers) but if he is a spark i will give him credit for knowing(should) know what he's doing but just seems odd to change the WM elem just as a trial and error method when it is an easy item to confirm or eliminate really.

 

[tombennetts]

have you installed anything new recently?

 

[mike-evans]

Yes he is a qualified spark, has been for about 30 years since he done his apprenticeship, he does not work on house electrics, hes a electrical engineer in a heavy plant/factory, but it all uses the same principles...He only had a meter with him, so unable to PAT test etc...This is the issue i got, I want a definate answer before I wack loads of money by just fault finding..One thing that stood out, we disconnected the WM element and run it, it run fine-Element at fault? But with this running, I turned on oven and it tripped the RCD..
Nothing has been recently upgraded/changed, exactly the same as it was 5 years ago..
The board only has 1 RCD, so I dont know what this tell you?

The bit that confusses me is, ok if the WM Element is faulty, that would make the RCD tirp-ok! but, cant understand why/how it would affect the oven??
My trade is Mechanical, so i might be applying Mech principles/ways of thinking here which could be miles of topic, and just confuses everything thing, so just excuse this..

My local Electrical call out company want £50 to come an have a look. for this I can replace both oven and WM elements..but might not be the fault.

 

[mogga]

WM Element turns faulty as it heats up and expands this causing the fault to develop By time its cooled down and contracted faults gone so when you put meter on it Hey presto No fault as for oven sounds like element on it YES it can happen 2 things going faulty around the same time

 

[Rockingit]

If it were me, I'd think about:

1) RCD's deteriorate through activiation, ie the more they trip (or are tested to trip) then the more unreliable they become - so ever decreasing circles.

2) Personally, I would get the leakage clamp meter out and see how much current is leaking BEFORE the suspect appliances are turned on. It's perfectly normal for healthy appliances to leak a little bit and the cumulative affect can cause issues.

3) Identify another circuit not on that RCD (assume you have a split board) and plug the washing machine into that side (via an extension lead) and see if the other RCD trips. Not the most technical of diagnostics I admit, but still effective. If you were careful to do so, you could also run up the cooker element this way too.

4) Both of these appliances are in the kitchen, right? So there is another common factor - the room itself. Any DIY recently? Any floods or leaks? IR the circuits thoroughly - FIL should be able to do this.

5) Thus far, you've not spent a bean. But if this helped, you can make a Help for Heroes donation!!

 

[Rockingit]

WM Element turns faulty as it heats up and expands this causing the fault to develop By time its cooled down and contracted faults gone so when you put meter on it Hey presto No fault as for oven sounds like element on it YES it can happen 2 things going faulty around the same time

I liked the old wind-up 4kV meggers for this!!

 

[mike-evans]

One thing I can add is, I use the tumble Dryer on the same ring main as what the WM is using (same 2 gang switch), what is the norm for a Tumble Dryer, 3KW?

does this confirm RCD is ok, and confirm faulty Oven and WM?

 

[kung]

A ramp test would tell you as said how is the oven wired ? plug in socket ? own radial ? do you get on with a neighbour ? if so see if you can plug the WM etc into an extension lead and pop it in next doors nearest socket ! some ovens run off a plug top and the hob is the item on its own circuit. what sort of oven is it ? did your F.I.L. test that ? what did he say regarding the oven ?