RCD tripping

[ray316]

Only started a week ago that the RCD keeps tripping but the circuit breaker’s don’t . I have switched each breaker off one at a time to see if the RDC still trips . I tried all the circuit breakers and the final one l tried was downstairs power circuit off and it didn’t trip .
I have then switched power on and tried unplugging one appliance at a time and it trips on any that l have took out , so lm confused where to look next .
I have a weatherproof outdoor Double socket and a switched fused spur in my outbuilding to feed a double socket and light switch.
One thing l have noticed is last night it was tripping a lot and it seems to happen when it’s raining .. Could it be a earth leakage somewhere on the ring circuit , can someone give me some help and advice.

 

[ETAF]

Disconnect all devices if possible
And switch off any sours
Often things like outside lights plugs get wet or full with water can cause an ussue
Or
Heaters like hair dryers washing machines dushwashers
Also motors
Fridge freezer
Can be easy sometimes
I have found laptop cables
Outside lights
Hairdryers
Washing machines
Cause issues

 

[ebee]

One thing it might be is water ingress in your outside socket. When I installed them on any but there own RCD circuit, I always put a double pole isolator inside the house. That way you could safely switch the outside socket off even if it on a circuit with other sockets on.
Please note - although you switch a MCB off (or remove a fuse) this will not disconnect the N pole and N to E faults can still cause RCDs to trip.

 

[DetlefSchmitz]

...
toasters
...

 

[ray316]

One thing it might be is water ingress in your outside socket. When I installed them on any but there own RCD circuit, I always put a double pole isolator inside the house. That way you could safely switch the outside socket off even if it on a circuit with other sockets on.
Please note - although you switch a MCB off (or remove a fuse) this will not disconnect the N pole and N to E faults can still cause RCDs to trip.

I have eliminated all MCB tripping the RCD apart from the downstairs Power.
I have switched all of apart from downstairs power and disconnected one appliance at a time and it still trips the RCD.
The switched fused spur in the outhouse is dry and covered but l have left had the front cover off (not screwed back on) for some time .. can a damp area cause this to happen.
Will a plug tester check for earth problems/ leakage, or how else can l pin down the area problem. I have a multi meter and l’m quite competent on testing electrics but l could do with some expert advance on fault finding this problem..

 

[Taylortwocities]

Multimeters and plug in testers won’t help. You’d need a special device called an insulation resistance tester.
Without one you will only becsbkd to use a process of elimination.

Please read carefully the posts above. You seem to have missed the important point.
Just turning off an MCB does not isolate a circuit. You would also need to physically remove the NEUTRAL wire ftom the neutral busbar inside the consumer unit.
Otherwise an earth fault on a neutral wire can trip the RCD even if the MCB is turned off.

But first, look at your outside electrics. Disconnect them ( both live and neutral wires!)
That’s often the cause of this sort of problem.

 

[ericmark]

We have three meters, the installation tester, the clamp on ammeter, and the RCD tester. Without them it is a bit hit and miss.

We should test the installation with at least 250 volt, normally 500 volt DC for leakage, but since DC it will not show inductive and capacitive linking, so also looking for less than 1/3 of rated valve leakage under normal running conditions (9 mA with 30 mA trip) and except caravans which is a special case, each RCD should be rated at 1/3 of the one feeding it.

So an outside RCD being fed from 30 mA RCD should be 10 mA.

But using a non trip loop impedance tester they draw around 9 mA so if it does not trip, then unlikely to be a problem later, and many use that rather than actually measure the leakage.

I will admit I did not have a clamp on which could measure down to 1 mA so playing safe was to fit all RCBO's (a RCD and MCB combined) to reduce build up of leakage.

We can only test with what we have, so if the installation resistance tester was not to hand, then use the PAT tester.

Earth - neutral faults can be hard to find, as often the neutral is not switched, so anything not in use, unplug it.

We look at likely culprits, the defrost element in freezer, outside lights and sockets, and any other item with mineral insulated elements, immersion heater, kettle etc.

And exposed elements like the toaster.

 

[JohnW2]

Please read carefully the posts above. You seem to have missed the important point. Just turning off an MCB does not isolate a circuit. You would also need to physically remove the NEUTRAL wire ftom the neutral busbar inside the consumer unit. Otherwise an earth fault on a neutral wire can trip the RCD even if the MCB is turned off.

That is all true but an N-E fault can only result in an RCD trip if there are loads drawing current. Hence, if one turns of all the 'other' MCBs and successfully disconnects all the loads on the one circuit that still has its MCB 'on', then there will be no trips, even if there is an N-E fault somewhere.

One can then try reconnecting loads to the circuit in question, one at a time. That may reveal the source of the problem or, if reconnecting several different loads causes trips to recur, suggests that there is an L-E fault somewhere in the wiring of the circuit.

Kind Regards, John

 

[Harry Bloomfield]

That is all true but an N-E fault can only result in an RCD trip if there are loads drawing current. Hence, if one turns of all the 'other' MCBs and successfully disconnects all the loads on the one circuit that still has its MCB 'on', then there will be no trips, even if there is an N-E fault somewhere.

There can still be some voltage differential between N & E, even if everything in the home is powered down - voltage from external sources and neighbours supplies.

 

[JohnW2]

There can still be some voltage differential between N & E, even if everything in the home is powered down - voltage from external sources and neighbours supplies.

That's very true. As I've explained in the past, it is theoretically possible to get RCD trips due to loads in neighbour's supplies, even if one has absolutely no loads in one's own installation - with the current due to neighbour's loads going 'backwards' through the RCD and hence via a N-E fault to earth.

However, with the common sort of 'faults to earth', due to water ingress or modest impairments in insulation resistance, I think that, in practice, the impedance of the fault is very unlikely to be low enough for the small N-E potential difference (due to neighbours) to result in enough current through the fault to trip a RCD.

In the (much less common) situation of a very low impedance N-E fault (e.g. a 'short') then I agree that almost any degree of N-E PD (due to neighbours) could cause an RCD to trip.

Kind Regards, John

 

[ericmark]

With a TT supply yes neighours load can show up a neutral - earth fault, and to some extent same with TN-S, not impossible with TN-C-S but unlikely.

But with main isolator off, testing earth - neutral with an insulation tester is easy, and likely first test any electrician would make.

Once one wants to go further and work out which circuit, then more involved. In the main we use experience and have a stab at likely culprits first, before starting a methodical hunt.

The problem is it's easy to get a build up, a few mA on many circuits, hence why I like RCBO's, but to undo each neutral and test takes time, and if not tripping all the time, then often the multi-meter in the form of a clamp-on ammeter is your friend, no need to open the consumer unit, or expose any live cables, you can clip it on and monitor the leakage, not always possible, but turning on items in turn, or unplugging and plugging in, often one can identify the 2 mA here and 5 mA there, which together builds up to trip the RCD, including faulty suppressors which would not show up with a DC test.

I know my house has around 24 mA leakage, spread over 14 RCBO's this is not a problem, but would likely be a problem had I gone for cheap option and used 2 RCD's.

But to suggest a DIY guy goes around with a 500 volt installation tester opening up his consumer unit and removing neutrals, I am not happy with, but to clamp the meter around main incoming supplies, and read leakage seems a lot safer?

I can see with a commercial premises one can cut costs with one RCD for many circuits when you have an electrician on site, but in domestic when the owner needs to employ an electrician to fault find if he can't find it, and likely has freezers plugged in, to save £50 by having only 2 RCD's instead of all RCBO's seems to be folly.

 

[JohnW2]

With a TT supply yes neighours load can show up a neutral - earth fault, and to some extent same with TN-S, not impossible with TN-C-S but unlikely.

With TT or TN-S, there is clearly a possibility that, even if there are absolutely no loads within the installation concerned, neighbours' loads (which inevitably raise the neutral potential to above true earth potential) can result in current flowing 'backwards' through the N-side of an RCD and hence through an N-E fault to earth - although, as I said, unless the 'N-E fault is of pretty low impedance, that current may well not be enough to trip the RCD.

With TN-C-S, it depends upon what you mean by a "N-E fault". If the building is constituted totally as an equipotential zone (i.e. all bonding in place etc.), then (with no loads within the installation), it is impossible for a fault between neutral and anything within the building (e.g. a CPC/exposed-c-p) to result in any current through the RCD, since the neutral is inevitably at exactly the same potential as the equipotential zone (joined at MET, with no VDs within installation). However, if the equipotential zone is imperfect and a fault develops between neutral and true earth, then the situation is exactly the same as with TT or TN-S.

Kind Regards, John

 

[ericmark]

TN-C-S means some where earth and neutral are combined as a PEN, it does not need to be combined at the house.

 

[JohnW2]

TN-C-S means some where earth and neutral are combined as a PEN, it does not need to be combined at the house.

Of course, but the installation's 'earthing system' (which will include everything 'earthed' if all required bonding is in place) is connected to that PEN in the house - so, as I said, in that situation there can never be a PD between the neutral; and anything 'earthed' within the property - so no prospect of current flowing 'backwards' through the RCD to any N-'E' fault within the property as a result of neighbours' loads.

Kind Regards, John

 

[ray316]

I remove the front cover of my waterproof outdoor double socket today and quite abit of water came out and the RDC tripped so l thought l had solved the problem . I wiped the inside of the box and wiring and noticed there was no grommet at the back where the cable comes in, so l have put sealant to block the hole .
This was at 1.00pm and now at 9.30 it’s just tripped again, so l’m now totally confused .
Can someone answer if any bit of water has entered the core and go down so far could this still trip the RDC .
The cable goes inside to a double socket so thinking of disconnecting from there to see if this might solve it .