Sockets tripping RCD after 10 - 15 mins

[R1804]

Hello,

Recently moved house, everything was fine for 1 a month or so. One morning I woke up to no electricity, narrowed the issue down to the sockets at the consumer unit, following this I unplugged all appliances and tried flipping the switch back to no avail, last area in the house was the conservatory - This has a fused spur and 3 double sockets, upon removing the fuse and trying the switch at the consumer unit everything stayed on.

I've had the sockets off, checked all the wiring for damage / loose connections and everything looks fine. When I popped the fused back in the electricity stayed on for 10 - 15 mins then the RCD tripped again.

Can anyone provide some advice as to what could be causing the issue?

 

[sparkwright]

Removing that fuse wouldn't disconnect to the neutral.

Was the fused spur switched or unswitched?

If it is unswitched, you need to disconnect the load neutral as well.

Work safely if you do this.

(If the fused spur is switched then the switch will disconnect both the live and neutral.)

 

[SUNRAY]

Hello,

Recently moved house, everything was fine for 1 a month or so. One morning I woke up to no electricity, narrowed the issue down to the sockets at the consumer unit, following this I unplugged all appliances and tried flipping the switch back to no avail, last area in the house was the conservatory - This has a fused spur and 3 double sockets, upon removing the fuse and trying the switch at the consumer unit everything stayed on.

I've had the sockets off, checked all the wiring for damage / loose connections and everything looks fine. When I popped the fused back in the electricity stayed on for 10 - 15 mins then the RCD tripped again.

Can anyone provide some advice as to what could be causing the issue?

I'll hazard a gues you have a fault. As it's a conservatory I'll make another guess it may be water ingress.

EDIT: This will require the use of an insulation tester. The sort of kit used by electricians.

 

[JohnW2]

I'll hazard a gues you have a fault.

Quite possibly, but rather an odd fault if it can be temporarily (but only for 10-15 mins) cured by disconnecting and then reconnecting the L.

As it's a conservatory I'll make another guess it may be water ingress.

Under normal circumstances, I'd agree. However, unless the OP's "UK" is in Scotland/NI or thereabouts (and hasn't had any plumbing leaks in his conservatory),the last few months have not been 'normal circumstances', such that 'water ingress' has presumably (temporarily) become a bit of a rarity!

EDIT: This will require the use of an insulation tester. The sort of kit used by electricians.

I'm not so sure about that. At least initial IR testing would do nothing more than to confirm the existence of a fault, without giving any indication where it is.

In the common situation of water ingress, just opening up all the relevant sockets (and other accessories, including ceiling roses) will usually rapidly find the problem (and, usually, also cure it, since things generally dry out pretty quickly once the water is 'released') - but it seems that the OP has already done that, without finding anything, so I'm not sure what's next!

As with many such cases, one possibility that often gets overlooked is a faulty ('trigger happy') RCD.

Kind Regards, John

 

[ericmark]

EDIT: This will require the use of an insulation tester. The sort of kit used by electricians.

I tend to agree, finding faults without one is not easy, however does not need to be calibrated, so the VC60 costs around £30 so not too bad, I got one when I could not find my Mega, when I did find it reading matched. Only down side is not low ohm range, only insulation tester and volt meter.

In the main faults are caused by water as already said, and if on the neutral load can make a difference.

A RCD tester is rather expensive, and I have had problems where the tester showed A1, but swapping the RCD cured the fault, no idea why, just know it did, both showed same results with tester.

My old house was a pain, around 1992 my son decided he wanted to be a radio ham, this was before we had consumer units, just a fuse box with the fuses replaced with MCB's, I had two fuse boxes so fitted two RCD's to feed them. So they have been in now some 30 years, over this time I would get batches of trips, no faults found, would trip repeatedly over 2 weeks, then 2 years before it would happen again. I blamed spikes on the supply, but result was the loss of freezers full of food when it happened when not at home, so this house all RCBO's.

Fault finding is often a case of luck, daughters it was a neutral wire touching the 3.5 mm screw on a socket, as she walked through the bedroom, some one had caught the neutral wire with a Stanley knife when fitting the socket, one house it was the freezers auto de-frost heater with a fault, since it was on a timer hard to find, found it testing neutral to earth.

Same goes for any device with timers, washing machine etc. Osmosis damp proofing etc can be a real pain to find, often don't even realise it has been fitted.

So going through my mind is what has a 10 - 15 minutes delay before auto switching on? Freezers often 4 - 5 minutes, but can't think of anything with 10 - 15 minutes, I would guess some load some where in house has switched on causing the neutral voltage to raise against ground, but can only guess.

 

[R1804]

Removing that fuse wouldn't disconnect to the neutral.

Was the fused spur switched or unswitched?

If it is unswitched, you need to disconnect the load neutral as well.

Work safely if you do this.

(If the fused spur is switched then the switch will disconnect both the live and neutral.)

Hi, thanks for the response.

The spur is unswitched - as it stands currently I've got the fuse removed and the RCD has not tripped again since doing this so I'm running an extension lead from one of my kitchen sockets into the conservatory temporarily.

 

[R1804]

I'll hazard a gues you have a fault. As it's a conservatory I'll make another guess it may be water ingress.

EDIT: This will require the use of an insulation tester. The sort of kit used by electricians.

Hi, thanks for the response.

No sign of water in any of the sockets, I've also checked the sockets on the opposite side of the same wall.

 

[R1804]

Quite possibly, but rather an odd fault if it can be temporarily (but only for 10-15 mins) cured by disconnecting and then reconnecting the L.

Under normal circumstances, I'd agree. However, unless the OP's "UK" is in Scotland/NI or thereabouts (and hasn't had any plumbing leaks in his conservatory),the last few months have not been 'normal circumstances', such that 'water ingress' has presumably (temporarily) become a bit of a rarity!

I'm not so sure about that. At least initial IR testing would do nothing more than to confirm the existence of a fault, without giving any indication where it is.

In the common situation of water ingress, just opening up all the relevant sockets (and other accessories, including ceiling roses) will usually rapidly find the problem (and, usually, also cure it, since things generally dry out pretty quickly once the water is 'released') - but it seems that the OP has already done that, without finding anything, so I'm not sure what's next!

As with many such cases, one possibility that often gets overlooked is a faulty ('trigger happy') RCD.

Kind Regards, John

Hi, thanks for the response.

Is there anyway of testing the RCD to see if its faulty? or is it just a case of replacing it? They're not expensive so that's not an issue.

 

[R1804]

I tend to agree, finding faults without one is not easy, however does not need to be calibrated, so the VC60 costs around £30 so not too bad, I got one when I could not find my Mega, when I did find it reading matched. Only down side is not low ohm range, only insulation tester and volt meter.

In the main faults are caused by water as already said, and if on the neutral load can make a difference.

A RCD tester is rather expensive, and I have had problems where the tester showed A1, but swapping the RCD cured the fault, no idea why, just know it did, both showed same results with tester.

My old house was a pain, around 1992 my son decided he wanted to be a radio ham, this was before we had consumer units, just a fuse box with the fuses replaced with MCB's, I had two fuse boxes so fitted two RCD's to feed them. So they have been in now some 30 years, over this time I would get batches of trips, no faults found, would trip repeatedly over 2 weeks, then 2 years before it would happen again. I blamed spikes on the supply, but result was the loss of freezers full of food when it happened when not at home, so this house all RCBO's.

Fault finding is often a case of luck, daughters it was a neutral wire touching the 3.5 mm screw on a socket, as she walked through the bedroom, some one had caught the neutral wire with a Stanley knife when fitting the socket, one house it was the freezers auto de-frost heater with a fault, since it was on a timer hard to find, found it testing neutral to earth.

Same goes for any device with timers, washing machine etc. Osmosis damp proofing etc can be a real pain to find, often don't even realise it has been fitted.

So going through my mind is what has a 10 - 15 minutes delay before auto switching on? Freezers often 4 - 5 minutes, but can't think of anything with 10 - 15 minutes, I would guess some load some where in house has switched on causing the neutral voltage to raise against ground, but can only guess.

Hi, thanks for the response.

I will check the wires again for damage. If it was a ground fault am I right in saying that the issue must be in the conservatory? (after the fused spur) or could this fault be somewhere else?

 

[ericmark]

If it was a ground fault am I right in saying that the issue must be in the conservatory? (after the fused spur) or could this fault be somewhere else?

No it can well be elsewhere, but since removing the fuse cures it, most likely in the conservatory.

A RCD measures the current in the line and neutral, collectivity called the lives. If the two are within 15 mA of each other it will not trip, and if greater than 30 mA it will trip, actual tripping point normally around the 25 mA but rules just say some where between the two.

So if current takes a different path, i.e. through the earth, then it will have a greater than 15 mA difference, but this can be either the line or the neutral which is allowing current to escape from the circuit.

With the line we can isolate by removing fuse, but not the neutral.

But neutral is nearly the same voltage to earth, so with line we look at MΩ but with neutral 80Ω would need 1.2 volt between neutral and earth to allow 15 mA to flow, the volts between earth and neutral increases with the load, and also the length of wire between where the earth and neutral are linked before it comes into the house to where the fault is.

So it can be really misleading, a bit of damp toast in toaster left plugged in, can trip the RCD when the kettle is used, but not the toaster, because the kettle uses more power.

I think this unlikely to be what is going on with you, but it may, so the way to test is to use a meter, first thing is switch off supply with the isolator, not the MCB as they don't turn off the neutral, isolators normally have a red operating leaver, then you test both line and neutral to earth using at least 250 volt, normally we use 500 volt.

Even this is not 100%, as the insulation tester uses DC, and our power is AC, and AC can have inductive and capacitive linking, so we should also test live with a clamp-on meter that the drain does not exceed 9 mA, I have never done this, as my clamp-on only measures down to 100 mA, I have just crossed my fingers.

But I do have an insulation tester, so when I have had a problem, I use that to find out where, I have never needed to use trial and error, we would normally say look for spiders in the sockets etc. But you have already removed them.

I looked at hire charges for an insulation tester, but at £55 per week, and new one for £35 clearly not really an option, a multi-meter is useless to find the fault, so either you buy an insulation tester, or you get an electrician who will have one. So you buy one of these or you get an electrician.

The question is if you buy one, could you use it? It does use 500 volt, so quite shocking if you get it wrong, and not sure I could safely instruct how to use one on the internet.

 

[ETAF]

does that fused spur , that you have just removed the fuse from, also run any lights in the conservatory , or just those 3 sockets.

 

[bernardgreen]

For what it is worth,

Apparently random tripping of an RCD was eventually tracked down to a defective security light. Only when its PIR sensor detected animals on the lawn did it switch on and trip the RCD,,

 

[SUNRAY]

Hi, thanks for the response.

I will check the wires again for damage. If it was a ground fault am I right in saying that the issue must be in the conservatory? (after the fused spur) or could this fault be somewhere else?

This time of year it could easily be bug infestation. Spaces filling with ladybirds or woodlice is not uncommon.

 

[R1804]

does that fused spur , that you have just removed the fuse from, also run any lights in the conservatory , or just those 3 sockets.

Hi, thanks for the response.

No, only the 3 sockets - The lights still work after removing the fuse.

 

[R1804]

No it can well be elsewhere, but since removing the fuse cures it, most likely in the conservatory.

A RCD measures the current in the line and neutral, collectivity called the lives. If the two are within 15 mA of each other it will not trip, and if greater than 30 mA it will trip, actual tripping point normally around the 25 mA but rules just say some where between the two.

So if current takes a different path, i.e. through the earth, then it will have a greater than 15 mA difference, but this can be either the line or the neutral which is allowing current to escape from the circuit.

With the line we can isolate by removing fuse, but not the neutral.

But neutral is nearly the same voltage to earth, so with line we look at MΩ but with neutral 80Ω would need 1.2 volt between neutral and earth to allow 15 mA to flow, the volts between earth and neutral increases with the load, and also the length of wire between where the earth and neutral are linked before it comes into the house to where the fault is.

So it can be really misleading, a bit of damp toast in toaster left plugged in, can trip the RCD when the kettle is used, but not the toaster, because the kettle uses more power.

I think this unlikely to be what is going on with you, but it may, so the way to test is to use a meter, first thing is switch off supply with the isolator, not the MCB as they don't turn off the neutral, isolators normally have a red operating leaver, then you test both line and neutral to earth using at least 250 volt, normally we use 500 volt.

Even this is not 100%, as the insulation tester uses DC, and our power is AC, and AC can have inductive and capacitive linking, so we should also test live with a clamp-on meter that the drain does not exceed 9 mA, I have never done this, as my clamp-on only measures down to 100 mA, I have just crossed my fingers.

But I do have an insulation tester, so when I have had a problem, I use that to find out where, I have never needed to use trial and error, we would normally say look for spiders in the sockets etc. But you have already removed them.

I looked at hire charges for an insulation tester, but at £55 per week, and new one for £35 clearly not really an option, a multi-meter is useless to find the fault, so either you buy an insulation tester, or you get an electrician who will have one. So you buy one of these View attachment 276262 or you get an electrician.

The question is if you buy one, could you use it? It does use 500 volt, so quite shocking if you get it wrong, and not sure I could safely instruct how to use one on the internet.

Thanks, I will give your instructions a go - If I can't find the issue myself I will look for an electrician, was hoping it would be something simple.