Emergency RCD replacement

[ScottishGasMan]

The RCD and CU was in the house when they bought it 25+ years ago and I dont believe any wiring has been done since. The MCB marked cooker I dont think feeds anything these days, not been a cooker switch that I ever remember being there, no access under floors to run any additional cable without pulling up old laminate that wont come out without damage.

I've had the full hager CU with RCBOs fitted in my own place on the advice of you guys on here a while back as while we've never had any trouble, I've worked in loads of houses with nuisance tripping over the years and would hate to be dealing with it regularly

 

[endecotp]

Fair point, but its got plastic feet and on a wooden floor, could it pass through them to ground?

Yes, especially if they are damp.

 

[endecotp]

Assuming somone did take the earth off the fridge and measured between it and the socket with a multimeter (fluke 115)

A max reading of 0.022A and when monitoring normally it would flash between 0.021 and 0.000 every second or so, that would be a lot for any one appliance to have going down the earth wouldn't it?

A safer experiment would be to unplug the fridge and measure resistance between live and earth.
What you really want is a high-voltage resistance measurement, but doing it with a multimeter could still be interesting.

 

[ScottishGasMan]

A safer experiment would be to unplug the fridge and measure resistance between live and earth.
What you really want is a high-voltage resistance measurement, but doing it with a multimeter could still be interesting.

I did that first and got an open circuit on it, but the multimeter isn't great for finding the likes of very small insulation issues or the likes, also dont know if theres any relays in the fridge, when doing short circuit and earth resistance checks on boilers you almost never find anything wrong as they wont have a direct connection to the faulty components until the relays are powered up.

 

[endecotp]

I did that first and got an open circuit on it, but the multimeter isn't great for finding the likes of very small insulation issues or the likes, also dont know if theres any relays in the fridge, when doing short circuit and earth resistance checks on boilers you almost never find anything wrong as they wont have a direct connection to the faulty components until the relays are powered up.

All true, but it was still worth trying. I had an outside light that tripped an RCD and it had a measurable earth-to-neautral resistance.

There is, of course, a thermostat in the fridge...

 

[seasickstevie]

... when doing short circuit and earth resistance checks on boilers you almost never find anything wrong as they wont have a direct connection to the faulty components until the relays are powered up.

Which is why it's often best to measure between neutral and cpc (earth), as the electronics and relays generally operate (and isolate) the live feed.

 

[ericmark]

If it has auto defrost or frost free, it could be the heater, common to find a mineral insulated heater to defrost, @seasickstevie comment measure neutral to earth is a good one.

 

[sparkwright]

To summarise a bit, the fault is either on one the circuits between circuits 1-5, or the RCD is faulty.

Usually it's not the RCD, but who knows.

You have been unplugging everything, which is correct. Only switching off at the socket is not good enough, unplugging is needed. All fused connection units and the like need to be turned off to. Does it still trip?

Someone asked if there was a socket on the cooker switch. If you can find this circuit, this would provide a supply for the fridge freezer, as it is non-RCD protected.

Obvious things to check are outdoor garden supplies which may be getting wet.

Others things to check are has any DIY been recently done? Such as drilling, loosening faceplates, fitting new electrical fittings??

Kettles, washing machines etc are likely suspects.

The lights and cooker supply are not RCD protected and should remain working.

Sorry to go over old ground, but thought I'd try to condense some of the info into one post.