Main rcd tripping

[BCM454]

Hello, my contactum b8003/2 30mA RCD feeds about 6 MCBs for light and power. Nothing had changed but suddenly my dishwasher seems to be the common denominator in tripping the main rcd. However, if I turn off all other MCBS, it doesn't trip. Please help me with my logic. This makes me think that the dishwasher, in combination with other things is now exceeding 30mA or whatever actual trigger leakage current of the main rcd, or the main rcd is now over-sensitive. I only put my dishwasher on overnight, so apart from router, standby TV and a few chargers, nothing else is running, but of course the refrigerator or freezer could cut in at any time. I moved the dishwasher plug to a socket on a different ringmain on the same master rcd, and it still tripped, so I hope there is nothing dodgy (mouse nibblage?) with its normal ring main.
Grateful to know if I put an rcd extension to test the dishwasher, would it or the main rcd trip first or is it down to the specific trip characteristics of each rcd and most sensitive trips first?
I remember the electrician having a job wiring in the main rcd as lots of cables in the fuse box , so replacing main rcd might be too tricky for me. Ideally I would love to put it on its own rcbo to have 30mA leakage to itself, but that's a major rewire. Grateful for advice and logic check. I would like to be sure if the dishwasher has gone faulty before replacing it.
Many thanks
Brian

 

[Wilko]

Hi - sorry to hear that your RCD has started tripping. Unfortunately there’s usually a good reason for this, one that should be found and fixed. From what you’ve said it seems likely your DW is misbehaving at some point in its cycle, perhaps when a pump starts for example. Sometimes this can be economically resolved but last time it happened to me at home I went shopping, just saying. To confirm what’s going on an Electrician could check that no other faults were present, measure the leakage currents and test the RCD was working correctly.

You make a good point that the leakage current can be reduced by unplugging things and isolating circuits, but in the end the DW leakage current (if that’s the cause here) is only likely to get worse.

 

[BCM454]

Many thanks. Is there such a thing as a leakage current measuring device to plug in in front of the dishwasher or perhaps fridge and freezer that I can then see a timeline of leakage current data?
If more likely to be the dishwasher, I had better order one soon so I do t face 6 months of washing up, on top of everything else!

 

[Wilko]

Hi - to measure leakage current its preferred to use a “clamp meter“ that reads to very low currents. The clamp meter goes around the conductors to be measured and means we don’t have to physically interrupt the circuit. They can be very useful but they are not cheap. Here’s one from Megger as an example -

Megger DCM305E Earth Leakage Clamp Meter

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www.test-meter.co.uk

It takes a bit of knowledge and skill to use the meter safely, so I’d still recommend asking your friendly local Electrician to call by and test your installation.

 

[BCM454]

Thanks, once again. That device is half the cost of a new dishwasher, so I'll have to pass. I used to have a current meter for my owl consumption unit, before smart meters and it looks interesting but I shall resist!
Stay well!
Brian

 

[Gavona]

. That device is half the cost of a new dishwasher, so I'll have to pass.

There are cheaper devices than that Megger that might do a decent enough job for us amateurs. BigClive has a youtube video "How an RCD / GFI works and troubleshooting rogue tripping "that shows one and also the special extension lead he wired up to allow you to clamp around live/neutral separately.
The devices I have seen referenced are around £80 without calibration wheras the megger is more like £200:

1. HandyMAN TEK775 AC Earth Leakage Clamp Meter -​

2. AMECaL ST-9810​

So, what do the professional think about these?
Would calibration be worth it?

(I have recurring but intermittent RCD nuisance (rather than fault) tripping that I am trying to isolate before I get the professionals in (And he fault has not shown up for 3 days now so its a lottery whether sperky would be able to find the culprit(s)). I'll post separately about that if needed. My testing and isolation to date leads me to the theory that I have multiple leakage sources across two circuits on the same RCD and have identified several devices that have been implicated more than once. I believe that I would be able to use a device like that without interfering with circuits themselves in order to narrow down the issue. I hope that the cost of the device will be offset by the time saving on the electicians bill and also in these times it will be a benefit if the electrician is able to spend less time in my house and visit fewer rooms.)

 

[Gavona]

hmm those two may be the same but rebranded. This looks different (better?) and similar pricing:

1. TM-EL9809 Earth Leakage Clamp Meter​

 

[Gavona]

Mini AC Leakage Current Meter - MP780050 looks to me to be the same as the first two but only £40 at CPC.Farnell I have ordered one rather than waiting for any responses - at that price it won't be too expensive a mistake and I can't believe the price will stay long. ​