I've got a problem thats causing the RCD to trip every couple of days. There seems to be an issue with the socket ring thats causing this (switch the socket MCB off and everything else works). I've tested for a short circuit on the socket ring using a multimeter and cannot find it - the resistance across live & neutral never falls below 60 ohms, even with appliances connected; when they're all disconnected the resistance is huge. The strange thing is that the socket ring starts working again after a few hours but will trip the RCD again anywhere between 30 mins and 2-3 days after being switched on. I've not made any changes to the electrical layout, not hammered any nails through wires etc. Any help with this weird problem would be appreciated.
Tripping RCD
- Thread starter RobertS
- Start date
Sponsored Links
You may just have an installation with a leakage to earth for natural causes very close to tripping the RCD. If you wished to see how close it is one can use a tester that adds controlled amounts of leakage (by switching in resistors between live and earth) until the trip fires. To be reliable with all appliances you need 10 to 15mA "in hand" in normal operation at least.
However, it is also possible that the imbalance is caused by a neutral to earth short, as this effectively bypasses one of the balance coils (one in Neutral one in Live).
Ideally do a DC resistance check between N and E with a 500v megger, but failing that a meter will pick up the worst. Expect a reading of at least megohms if everything is in good working order. You will need to make sure the neutral of the circuit under test is disconnected at the supply as well as the live while you measure this, as neutral and earth are already connected by your electricity supplier, either at their substation or transformer, or in a PME system, by your meter.
otherwise, a simpler test, unplug everything, and then energise the socket circuit - if it doesn't trip, it is probably one of the appliances (though it could be a neutral earth problem even so- some live current is needed before such a fault will trip the breaker).
Some electronic appliences have filter caps between L and E that can leak a few mA each, so you only need perhaps 10 such objects to bring the trip to its limits.
If you are very sure of your socket's polarity, you can measure a suspect leaky appliance's earth current, even on an RCD protected supply that would normally trip, by putting a meter on AC amps between the earth core of its flex and the neutral of the supply and connecting nothing to the earth of the supply. More than 3mA on anything that does not specifically say otherwise is suspicious. During this test, treat the case of the appliance under test as if it is live, and have nothing that is really earthed either connected to it or within accidental reach (say 2m) if the socket is reverse polarised, or the meter fuse fails (yes it can happen !) it will be! Connect or disconnect the meter only with everything unplugged at source, and keep the test time to a minimum to get a good reading. This is a potentially dangerous test, and should only be performed if you truly understand what might go wrong. I am not really recommending this, only saying it can be done, with great care.
Otherwise better to refer any suspect appliances to someone experienced who can test it safely.
regards M.
However, it is also possible that the imbalance is caused by a neutral to earth short, as this effectively bypasses one of the balance coils (one in Neutral one in Live).
Ideally do a DC resistance check between N and E with a 500v megger, but failing that a meter will pick up the worst. Expect a reading of at least megohms if everything is in good working order. You will need to make sure the neutral of the circuit under test is disconnected at the supply as well as the live while you measure this, as neutral and earth are already connected by your electricity supplier, either at their substation or transformer, or in a PME system, by your meter.
otherwise, a simpler test, unplug everything, and then energise the socket circuit - if it doesn't trip, it is probably one of the appliances (though it could be a neutral earth problem even so- some live current is needed before such a fault will trip the breaker).
Some electronic appliences have filter caps between L and E that can leak a few mA each, so you only need perhaps 10 such objects to bring the trip to its limits.
If you are very sure of your socket's polarity, you can measure a suspect leaky appliance's earth current, even on an RCD protected supply that would normally trip, by putting a meter on AC amps between the earth core of its flex and the neutral of the supply and connecting nothing to the earth of the supply. More than 3mA on anything that does not specifically say otherwise is suspicious. During this test, treat the case of the appliance under test as if it is live, and have nothing that is really earthed either connected to it or within accidental reach (say 2m) if the socket is reverse polarised, or the meter fuse fails (yes it can happen !) it will be! Connect or disconnect the meter only with everything unplugged at source, and keep the test time to a minimum to get a good reading. This is a potentially dangerous test, and should only be performed if you truly understand what might go wrong. I am not really recommending this, only saying it can be done, with great care.
Otherwise better to refer any suspect appliances to someone experienced who can test it safely.
regards M.
I would also be suspecting a faulty appliance. You can learn a lot without doing any potentially dangerous tests just by careful observation over time. You've already pinned the problem down to a single ring main so why not take this approach a bit further.
Take note of what is and isn't switched on at tripping time. Don't forget things like central heating pumps that go on and off by themselves. If you have any outdoor electrics you should check to see if it's raining. If you suspect any single item, disconnect it and wait.
Take note of what is and isn't switched on at tripping time. Don't forget things like central heating pumps that go on and off by themselves. If you have any outdoor electrics you should check to see if it's raining. If you suspect any single item, disconnect it and wait.
Ok. from your post it sounds as though you have not made any changes recently to wiring, mcb, consumer unit etc. Hope that is correct? It is of course possible that something else (mice, beetles) has been making alterations on your behalf.
Next, what circuits are run through the RCD, and what others are there?
Third, slow RCD tripping is possibly because there is about 30mA of leakage somewhere. Less and nothing happens. More and it trips fast.
This leakage may be coming from more than one source. So although tripping only ever occurs if the ring mcb is on, it still might be 25mA leak on that circuit and 10mA on another. If only the suspect ring is on, and everything else is off, does it still trip?
Assuming you can really track it to just this one ring, does it trip if you have disconnected everything from the circuit. And I mean everything. Surprisingly easy to miss a socket or fan heater or outside light which have somehow got tacked on to the circuit.
If it does not trip with everything disconnected, then start putting things back one by one. Unfortunately it might be a combination of things. Heating elements in cookers, kettles,immersion heaters sometimes do this if a little damp has got inside the element. This moves around when they get hot and it turns to steam. Computers and the like may have surge suppressors which can leak.
If there have been any changes to the circuits, then we can discuss them
Next, what circuits are run through the RCD, and what others are there?
Third, slow RCD tripping is possibly because there is about 30mA of leakage somewhere. Less and nothing happens. More and it trips fast.
This leakage may be coming from more than one source. So although tripping only ever occurs if the ring mcb is on, it still might be 25mA leak on that circuit and 10mA on another. If only the suspect ring is on, and everything else is off, does it still trip?
Assuming you can really track it to just this one ring, does it trip if you have disconnected everything from the circuit. And I mean everything. Surprisingly easy to miss a socket or fan heater or outside light which have somehow got tacked on to the circuit.
If it does not trip with everything disconnected, then start putting things back one by one. Unfortunately it might be a combination of things. Heating elements in cookers, kettles,immersion heaters sometimes do this if a little damp has got inside the element. This moves around when they get hot and it turns to steam. Computers and the like may have surge suppressors which can leak.
If there have been any changes to the circuits, then we can discuss them
Sponsored Links
Thanks for all the suggestions. I'm going to try switching the other circuits (2 light, immersion heater & cooker) off & see if the socket ring will stay on. There's one socket outside that was fitted ages ago by a certified electrician - it's got a decent looking weather seal on it & everything seems dry. I did find an outside light tacked onto the socket ring - disconnecting the spur made no difference. As far as I can tell, this problem doesn't go away even when everything is unplugged from the socket ring but I'll double check this...
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
