RCD Tripping

[Jeff Gaines]

I have an RCD for the upstairs ring and a separate one for the downstairs ring. Lights, oven, boiler are on their own fused circuits.

The downstairs RCD tripped three times yesterday morning but I couldn't find any problems, In the end I turned off the dishwasher and all was well. Later I ran the dishwasher again and it ran all the way through its cycle, no problems.

I know it is sensitive, when a neutral and earth touched when I was fitting a new wall stat it tripped (even though the stat is on the boiler circuit).

Seems like a daft question but but I'm running out of ideas is it possible that work in a neighbour's house using electric tools could impact on my RCD? The houses are detached.

[The Natural Philosopher]

Not in terms of an earth neutral short - that has to be downstream of the RCD to trip it - but definitely in terms of them maybe causing spikes on the line, which in combination with mains suppression filters can cause high line to earth currents.

However my instinct here is you have a case of what I had - a direct earth to neutral short somewhere in the house wiring. These simply don't respond to 'switch this ring off and see' fault finding, because neutrals don't normally get isolated.

In my case I got near to the issue by noting that one ring was extremely prone to it, when using anything with a high switch on current. I was able to isolate the ring completely and probing with an ohmmeter showed reducing resistance between earth and neutral till I got to where the short was.

In essence you would test this by turning off thee house, and disconnecting each neutral at the CU busbar and measuring its resistance to earth. Leave kit plugged in and switched on, and if you find a shirt on any ring, then start pulling equipment off and testing that.

You may also find a fried rodent across neutral and earth - and live too.

OTOH it might well be a case of dampness causing tracking.

Or a failing mains filter capacitor

For a first stab try disconnecting the dishwasher and measuring earth to neutral and earth to live on the appliance itself.

[David Wade]

Sounds like the dishwasher is the issue. If something has water ingress, which dries, then these are typical symptoms.

Well yes, its current sensing and neutral and earth are only bonded at entry to the house, so may be at different potentials due to differences in wiring resistance. If current flows from neutral to ground, while nothing is flowing on the live, it will trip.

Generally no, it senses the current difference between live and neutral So for it to trip current would have to flow from you live (or neutral) into next door.

This can only happen if you have links between mains powered devices. A common cause is linked fire alarms, where one is connected to the upstairs lights, one to the lower, and they are then linked by a single wire.

Dave

[The Natural Philosopher]

Needn't be water ingress..

[Robin]

If you've not already read it I suggest you look at

Note especially that if turning off the d/w removes the problem it doesn't follow that the d/w is the real culprit. You might e.g. have leakage of 25mA on something else that is on only intermittently. When the d/w comes along and adds a modest 5mA the RCD trips. The d/w gets all the blame even though it may be doing nothing new.

[Adam Funk]

Definitely ingress, though!

[Jeff Layman]

Where was the dishwasher "turned off"? I had a problem with my Beko tumble drier tripping the RCD when it cooled down. It was the mains filter which was responsible (leaky capacitor?). But the filter is where the mains cable enters the tumble drier and before the on/off switch. Only by turning off at the wall socket or pulling the plug was the tumble drier disconnected from the mains.

[David]

Just noting that this is why when we refurbished the house I had the CU upgraded from RCD to RCBO.

Earth neutral trips were the bane of my life when changing things like light fittings; notably outside lights.

Cheers

Dave R

[Jeff Gaines]

Just to say many thanks for all the replies and the guide sheet :-)

I will start with the dishwasher as I need to try and adjust one of the feet on the washing machine that is next to it so I can do it all in one. After that it's Poirot hat on.....

[John Rumm]

Have a read through:

[Brian Gaff]

Probably depends which mains phase they are on. Brian

[Brian Gaff]

Pardon me for being thick, but if the short is between Earth and neutral, does it matter given that most switches only disconnect the live. What condition might it be protecting from, assuming you are not silly and put an Axe through the mains cable, which is hardly likely.That would just blows a fuse. Brian

[ARW]

A photo of your CU might help.

Adam

[John Rumm]

Earth neutral shorts are prone to causing nuisance trips in an unpredictable way, since they require the neutral potential to be far enough away from the earth potential to pass 30mA to it. That only happens when there is adequate load on other circuits (TN-C-S) or other circuits and other properties (TN-S) to lift the neutral potential a bit.