RCD tripping, but with no fault

[roukel01]

Morning All

I was called to a property the other day. Dual RCD board. One of the RCD's is tripping most mornings between 4am - 6am.

Check the board, only 4 circuits connected to that RCD, 1 socket circuit (upstairs sockets), 1 lighting circuit, smoke alarm circuit and outbuildings supply.

Tested all of the circuits seperatley, all readings above 5 Meg Ohms.

Couldn't find anything wrong anywhere, this has only just started to happen too, but it ONLY happens between 4am - 6am. Nothing plugged in thats on a timer etc.
Tested RCD out, and that seemed to be working as it should

Any ideas?

 

[44ALLAN]

Outside light on day/night sensor

 

[telectrix]

definitely suspect outbuildings. try isolating the feed ( L and N) and see what happens for a couple of days. have you ramp tested the RCD?

 

[roukel01]

Ramp tested RCD, it was working fine

Outbuilds are now isolated, I'm seeing what happens there. Its the 4am - 6am that puzzles me, it never ever trips at any other time, and there's nothing plugged in in the outbuildings.

When we initially turned the power back on after testing, the security lights outside came on and worked fine.

 

[telectrix]

there's also the possibility of a fault under floor. client gets up to go to the bog, pressure on floorboard causing fault on a cable with a nail in it????

 

[roukel01]

Its the phone that bleeps when the power is cut that wakes her, plus we walked all over the house with the power on, and nothing happened.

 

[telectrix]

just a process of elimination then. if the outbuildings being isolated solves the problem then investigate that circuit. if not go to plan B. just a case of tracing it down circuit by circuit, then point by point. hope that you're charging by the hour. :sunny:

 

[roukel01]

Its hard to trace when there's no fault during the day! (but yes, its a time and material job!)

 

[Octopus]

As you've only got 4 circuits on the RCD and you've tried disconnecting 1 circuit, I'd be looking to disconnect another - yes not ideal for the client but it may be the only way.

Is it a dual board or could you fit RCBO's instead?

 

[roukel01]

thats a point, RCBO's could be used, I'll give it a couple of days to see if the outbuildings has solved it.

 

[chopper76]

Timers/boiler, possibly the fridge it does a whole set of different things during the night with the compressor because the doors not being opened and shut like it is during the day

 

[Glen Window]

could be a lots of things

 

[odawire]

central heating system switching on? maybe try linking out the stats on the heating controls and test again?

 

[markc123]

Aye, as chopper said and seeing as though you've pretty much tried everything normal - the fridge kicking in and out could be a real possibility.

Disconnect the fridge and if they moan about food going off...it'll be alright for at least 24hours.

Failing that, and what others have suggested...i think it could be the boogey man switching it off during the night.

 

[GLENNSPARK]

if its 4-6 AM that this manefests itself...then its got to be something timed....
have a look again at whats on them finals.....