Tipping RCD oddity

[VWW]

Hello all

Last week my RCD tripped. I narrowed it down to the downstairs socket ring as the culprit. Turned everything off, RCD back on, and then all devices turned back on without it tripping. This was okay for a few days. Same thing happened earlier this week, however I left the RCD off and left it to an electrician, who basically did the same as me and said there wasn't much he could do as it was now working... I've just got home after a weekend away to a fridge of ruined food...it's happened again. I've worked out the trip happened on Friday night. Again, the RCD kept tripping if I turned on the downstairs ring, but once I'd turned all appliances off, turned the RCD back on, and then appliance on, all seems to be okay again.

I'm at a bit of a loss... I wouldn't be surprised if it was a mouse chewing through some wires, but I don't understand why turning devices on and off suddenly makes everything okay.

Any suggestions welcomed.

[thebraketester]

Find a better electrician.

[mrmistoffelees]

Earth leakage, specifically on something that might have variable loads such as a fridge, washing machine or similar. Alternatively, earth leakage across everything increasing just past the tolerance. You've said you've tracked it down to the downstairs ring but that may just be the straw that breaks the camels back as it depends on what else that RCD is protecting. If it's just the downstairs ring then that makes sense but if it's an accumulation of earth leakage across other stuff too then you're not resolving the overall cause, just bringing it down to acceptable limits. Ideally you'd want to be looking at maybe doing an EICR (£150-£200ish) which would give an indication as to any wiring side faults. If you're seeing high earth leakage on a specific socket or circuit then this might help track down where to look. If this is all good then it does point towards a device, so here it might be worth buying an extension lead and running stuff temporarily from another ring if you can.

[119]

My money is on the fridge or freezer or fridge/freezer.

[FMOB]

[redacted]

[RECr]

Have you a lot of circuits on one RCD? That can lead to lots of small earth leakages adding up to the 30mA to trip the RCD. Its why dual RCD consumer units and these days, RCBOs (basically RC protection within each MCB) are generally installed.

My parent's house must have a dozen circuits on one RCD. Using a steam iron will trip the RCD pretty much every time.

[VWW]

Thanks all.

The whole house is on a single RCD (I've lived here for a year and only had issues in the past couple of weeks - no new appliances either), but when it happens everything goes back on happily except the downstairs ring (which trips the RCD again). I've put the fridge on an extension to the upstairs ring, so time will tell...

The bit I don't understand is why turning the downstairs ring back on consistently trips the RCD until I turn all of the appliances off. Then I can successfully bring then back on one by one.

[Mr Pointy]

Try changing the RCD?

[Belle427]

Fridge freezers are common culprits, the freezer defrost cycle usually does it which can happen at odd times.

[OutInTheShed]

VWW said:

Thanks all.

....

The bit I don't understand is why turning the downstairs ring back on consistently trips the RCD until I turn all of the appliances off. Then I can successfully bring then back on one by one.

You can get all sorts of odd effects.

You could have one or two marginal appliances which have a bit of earth leakage.
Your breaker ahould greak when the leakage exceeds 35mA
If you've got a couple of 15mA leakages then the breaker will be prone to random tripping from spikes and a few mA here and there from the surge of switching on can trip it.

Sometimes a plug-in RCD breaker can help isolate the culprits, as they tend to trip at a lower level.

Proper job is to leakage test all the appliances and the wiring.

Some stuff has filters on the the mains inputs to reduce electrical noise or trap surges. This can allow a small leakage.
Some of the 'surge protected' 4 way sockets sold for computers can have iffy amounts of leakage, or fail that way.

Last time I looked at this problem for a mate, the kettle was the culprit.
Anything involving water and elctricty is suspect. Fridges come into this category due to condensation etc.
Everything else is supect too!

If you are forced to use an electrician, get one to do a proper job of testing and consider splitting the various circuits onto RCBOs then only one ring will trip.

[Danns]

https://cpc.farnell.com/multicomp-pro/mp780050/min...

for £40 you'll be able to narrow it down rather quickly, and see what is/isn't making a contribution to the leakage in real time by plugging/unplugging the loads at the far end.

Tried and tested, what I used to narrow down my nuisance tripping - a dodgy light fitting coupled with leaky oven element on the same side of the board.

This of course depends on your level of competence/confidence and to start will involve taking cover off of your consumer unit.

[cookie1600]

Had a similar issue a couple of years back which threw our electrician for about half an hour checking leakage, until he pinned it down to the piezoelectric unit on our gas hob. Disconnected that and haven't had any issue since.

[kambites]

VWW said:

The bit I don't understand is why turning the downstairs ring back on consistently trips the RCD until I turn all of the appliances off. Then I can successfully bring then back on one by one.

One possibility is that you have two devices with marginal earth leakage characteristics. Many devices draw a lot more power for a short period after power on (can be anything from a few ms to a few seconds, depending on the device). If that's the case, switching the two marginal devices on at exactly the same time would create enough of an earth leak to blow the RCBO whereas turning them on one at a time wouldn't.

Such a fault could also be effected by humidity and/or temperature, which would explain why it sometimes trips on its own and sometimes doesn't trip when you turn everything on at once.

[Agent57]

Tipping RCD ?

If RCD gives a great service then 10-15% tip seems about right.

If it gives poor service, then no tip.

[VWW]

Bit of an update:

The downstairs ring tripped again last night, but this time it wouldn't come back with everything unplugged. I called in an electrician today who ended up finding that at least one of the socket connections was "double earthed" after likely being nibbled on by mice. He's moved this to the upstairs ring. I'm not exactly sure how this stops boards single RCD tripping. He also said half of the wiring is very old (red and black) and would need replacing at some point, but I should be sorted for now.

Fingers crossed...

[GasEngineer]

VWW said:

Bit of an update:

The downstairs ring tripped again last night, but this time it wouldn't come back with everything unplugged. I called in an electrician today who ended up finding that at least one of the socket connections was "double earthed" after likely being nibbled on by mice. He's moved this to the upstairs ring. I'm not exactly sure how this stops boards single RCD tripping. He also said half of the wiring is very old (red and black) and would need replacing at some point, but I should be sorted for now.

Fingers crossed...

Glad you got it identified.

What is meant by double earthed?

[Fore Left]

VWW said:

Bit of an update:

The downstairs ring tripped again last night, but this time it wouldn't come back with everything unplugged. I called in an electrician today who ended up finding that at least one of the socket connections was "double earthed" after likely being nibbled on by mice. He's moved this to the upstairs ring. I'm not exactly sure how this stops boards single RCD tripping. He also said half of the wiring is very old (red and black) and would need replacing at some point, but I should be sorted for now.

Fingers crossed...

I'm no electrician but that sounds like complete bks to me.

How the hell do you move a socket from one ring main to another without major surgery and something is either earthed or it isn't.

[Rough101]

Red and black PVC wiring doesn’t need replaced……

No idea what double earthed means either, or why it would result in leakage. Procedure would be to unplug all appliances and megger the circuit, then check continuity, then a Zs and polarity check, I’d also be testing the RCD itself. Houses with steel conduit have multiple earth paths, but if there is a cables CPC you don’t need to bother with the high current earth tests that were done on circuits that relied on the containment for earthing.

Your upgrade wouldn’t be to wiring unless it’s damaged or a crap job, it would be to RCBO’s in a new consumer unit.

[Sheepshanks]

Fore Left said:

VWW said:

Bit of an update:

The downstairs ring tripped again last night, but this time it wouldn't come back with everything unplugged. I called in an electrician today who ended up finding that at least one of the socket connections was "double earthed" after likely being nibbled on by mice. He's moved this to the upstairs ring. I'm not exactly sure how this stops boards single RCD tripping. He also said half of the wiring is very old (red and black) and would need replacing at some point, but I should be sorted for now.

Fingers crossed...

I'm no electrician but that sounds like complete bks to me.

How the hell do you move a socket from one ring main to another without major surgery and something is either earthed or it isn't.

I could only think he’s moved the circuit at the consumer unit?

[Chris Stott]

Replace the RCD.

They don’t last forever and aren’t expensive (or difficult) to replace.