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Why does this keep happening? RCD's and Consumer unit faults

Postby Paul A » Thu Aug 07, 2008 6:52 pm

Help - I've got a 3year old Hagar consumer unit UECOS48-6H It's performed faultlessly up until now but in recent weeks it has taken to tripping the RCD Controlled Circuits switch at varying times - middle of the night and mornings - this appears to bear no relation to the devices connected - we have tried isolating all devices linked to the ground floor circuits - and it only trips the ground floor and never the three trips associated with the ground floor i.e. 1) Smoke Alarm, B6. 2) Ground Floor Circuits, B32 3) Kitchen sockets B32. Never anything else.
The one device we have kept plugged in is a fridge freezer which I put an RCD plug safety device on - thinking that if it was the fridge freezer it would trip first but No... RCD trips anyway leaving all other trips on.
The line to ouside loads - eg lights is isolated and the fault continues.
When the RCD is returned to live it never trips out until the next time...
Does anyone have any ideas about further fault finding???
Regards Paul
Paul A
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Postby sparx » Fri Aug 08, 2008 5:15 pm

Hi Paul A,
This is clearly an earth fault and not due to overload which would cause circuit mcb to trip so the only real way to find cause is with an Insulation tester on each of the 3 affected circuits, one at a time.
Unless it is practical to unplug/disconnect everything on each circuit the only way to do such tests is to connect L to N and test between them & earth with appropriate test gear.
This is most definitely not a DIY job as not only does it require expensive equipment but also someone with the know-how to use it,
sorry needs a pro!
regards SPARX
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Postby ericmark » Fri Aug 08, 2008 7:52 pm

Hi Paul,
I agree with Sparx there is very little you can do to isolate the problem. An extension lead and trying to run items from a non RCD protected outlet may help find what it is but even with the test gear it’s not so easy to find what has gone wrong.
The “RCD plug safety device” will most likely have same rating as the one already installed in the house and unlikely to trip. I know my wife was persuaded she needed one for the lawn mower which I took straight back and asked for 10ma version which it seems although made are very rare and because time also comes into the equation it still may not trip first.
The fridge/freezer is a good thing to look at as it may have a defrost timer also anything else that randomly runs like central heating.
Last edited by ericmark on Sat Aug 09, 2008 8:47 pm, edited 1 time in total.

Postby TOPSPARK » Sat Aug 09, 2008 2:35 pm

Best advice I can give you on this matter is call in aregistered electrician and have him do a periodic inspection and tes on all the circuits and hopefully he will find the fault and be able to repair it with little fuss
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