New kitchen circuit - dishwasher tripping RCD

[mbelectric]

I installed a new kitchen ring about 3 weeks ago ready for a new kitchen to be installed, the customer wanted a grid switch arrangement to isolate the dishwasher, washing machine and fridge.
They called me last week to say that the main switch RCD suddenly started tripping on a regular basis (few times a day). I started the process of elimination and found that when the dishwasher was switched off no tripping occurred. I then plugged the dishwasher into a different circuit and no tripping occurred. I IR'd from the grid switch to the socket and got >299 on all 3 readings. I checked the socket and it was ok.
I haw now a bit flummoxed as to what the problem could be. If you switch the dishwasher on it will trip within 5 minutes, you can reset it and it will trip again after a few more minutes.
The only thing I can think off is the grid switch itself. The dishwasher worked ok for about 1 week before the problem started.
Any thoughts would be appreciated.

 

[bongos]

When you plugged the dishwasher into a different circuit and it didn't trip - was this still on the same RCD?

Just wondering if maybe the dishwasher is giving a fair bit of earth leakage and when combined with other items plugged in on the same circuit, it is causing the RCD to trip? What was the ramp test like for the RCD?

 

[JohnD]

washing machines tend to have quite a lot of background earth leakage. If the dwr is on the same RCD as other watery appliances, it may be enough to reach the 30mA trip.

hooray for RCBOs!

 

[mbelectric]

Just an update on this. I plugged the dishawasher into the washing machine socket (on same grid switch). After 10 minutes the breaker tripped - Not the RCD - after resetting the dishwasher went on to finish the cycle. The washing machine has worked fine on numerous occasions.

Bongos - The ramp test was 25ma.

 

[Taylortwocities]

So, breaker trips on overload, yes?

What is connected to that grid switch?
What is the value of the contact breaker that trips?
Is it only the grid switch on that breaker, or other stuff?
Have you got a clpamp meter? - can you determine the normal running cuurent without dishwasher of that circuit?

 

[securespark]

OOI, if you do an RCD test from a socket outlet with the d/w in circuit, is the test satisfactory?

 

[chadfieldpropertyservices]

Had a similar problem with a dishwasher tripping the RCD, turned out to be a duff heating element

 

[mbelectric]

Thought I would post an update on this in case you thought I was being ignorant in not replying. I went away for a couple of weeks (they were regular customers and were not bothered about lack of dishwasher). When I returned I decided to go back to basics and do all tests as if new install. (I Borrowed a PAT tester to test dishwasher and it passed ok).
During the IR test from CU got a straight short between P-N. I knew I had unplugged everything so started to remove sockets and test between each one. Removed one socket and the N popped out. Aha I thought gotcha, then I realised there were 3 cables in the socket (I had not made any spurs). I queried this with the customer and it turned out that just before the kitchen was fitted the customer had decided that he wanted a double socket in the lounge which backed onto the kitchen so he had taken a spur from the kitchen socket and drilled through the wall.

Apart from the Notification ramifications of doing this I also explained that I had just pumped 500v into his 46" plasma and associated electrical stuff plugged into the new socket.

Anyhow, after doing the appropriate re-testing and re-connecting the dishwasher now works ok. On hindsight I should have checked for a loose cable before anything else but I had managed to convince myself that as nothing else was causing the tripping the problem must have been between the grid switch and the appliance.
Alls well that ends well. Thanks for the help.