Strange RCD tripping scenario

[Rkidcd]

You'd have to see if the disconnection times could be met based on Ze, have you I.R tested every circuit L-E and N-E ?

Initial verified them all yes - not since tripping though as only happened this afternoon - gonna have to delve into it tomorrow

 

[marconi]

Re OP's #1: Which two final circuits?

You mention a TN&N board converted to SP. How many final circuits are there?

Suggestions:

Test the IR of electric ovens, hot wire element electric hobs, washing machines and tumble dryers and dishwashers, immersion heater.

Take a close look inside any outside light fittings and switches.

Pour 2-3 gallons of water around the earth electrode.

Check tightness and solidity of all connections.

Carefully remove sockets and look behind them for securing screws close to live conductors.

 

[Octopus]

^^ AND ramp test the RCD.

 

[Wilko]

Hi - Agree Murdoch and Strima I would not change out 100mA S type without a test result showing it's at fault. As others have said, it's quite likely a N-E fault exists. If it's in a final circuit unfortunately the single pole rcbo won't remove it from play.
Some questions and thoughts -
What parts of this installation are new?
Any patterns to the tripping?
What is the site Ze? Locate the rod and confirm the impedance of connection from rod to MET and CU earth bar with wander lead. Repair if required.
How long is the underground SWA linking cabinet to CU? What protects this cable? What were the cable IR results please? Carefully check all connections from cutout to CU and the polarity.
Happy Hunting

 

[Octopus]

^^ and don't forget to check the IR between L - SWA and N - SWA

 

[shaun1]

You could ramp test the RCD first with everything off and then with everything on to get an idea of leakage current on the installation.

 

[Deleted account]

I vote it could be accumulation of I.R. Do a bulk I.R test across all circuits.

 

[sam400]

Suggestions:

Test the IR of electric ovens, hot wire element electric hobs, washing machines and tumble dryers and dishwashers, immersion heater.

Out of interest how do you test the element in the appliance? Do you have to dis-assemble?

Cheers

 

[marconi]

Yes you need to gain access to the elements terminals and isolate them first.

 

[marconi]

Beko Tumble Dryer Heater Element | eSpares - https://www.espares.co.uk/product/es1435433/tumble-dryer-heater-element?pageNumber=1&PartTypeId=1584&ManufacturerId=927

espares and similar companies do short video clips showing how to gain access to heater elements and swap them. The link above is for a BOSCH tumble dryer for example. ( I know the link says BEKO but scroll down to see its a BOSCH machine).

 

[TJ Anderson]

Yes you need to gain access to the elements terminals and isolate them first.

Or.....stop wasting time and suss it out quick.

Put your earth leakage clamp around L&N at stare at screen whilst someone else is running around turning stuff on. You will pin point it very soon, If you don't have one buy one. They are cheap.

 

[weevilward]

I agree with the earth leakage clamp approach to see where the leakage is coming from. Could be cumulative across that many final circuits, without tripping individual RCBOs. I've seen 'normal' leakage on a 7-way board cause a 30mA incomer to nuisance trip, so it's feasible that all your final circuits could do the same to a 100mA. Unlikely, but feasible.

One last thought - I fitted a Lewden (aka Control Gear) 100A 100mA type S a few years ago and kept getting called back for nuisance tripping, when the 30mA downstream never batted an eyelid. All IR tests >99M. I replaced it with an MK type S and never been a problem since. Funnily enough I don't use Lewden RCDs anymore!