Electric sockets tripping - mystery! Need help finding solution

Brief description of problem.
Electric sockets only are tripping randomly - happened four times since moving into our new property on 22/5/09. The first time was two days after moving in, when barely anything was plugged in. The house was rewired a couple of years ago and the previous occupants state they had a similar problem, but it only happened to them a couple of times in the 2 1/2 years they were there. The most recent trip was at 1am this morning. When it trips, only the electrical sockets in the house are knocked out.
In locating the fault, I'm making some assumptions: chiefly that if all of the sockets are turned off (ie. no device is consuming power), its unlikely that anything could trip the RCB. With that in mind, the only devices consuming power at 1am in the morning are fridge, freezer and combi boiler all of which work on timers/thermostats. Therefore, one of these devices (or the RCB itself) must be at fault?
The kettle was originally suspect - on two of the four occasions, it had not long boiled when the trip occurred. I tested this two nights ago by boiling a full kettle load of water (twice) and then pouring it away. Tripped both times a few minutes after boiling when the kettle was off its base. Tried plugging the kettle into the living room sockets instead - tripped. Replaced kettle. At 1am this morning however when it tripped, the kettle hadn't been used for several hours.
Is it possible the RCB is a fault? I can leave the fridge and freezer doors open, combi boiler running and it doesn't trip so could it be a fault with one of these causing a power spike when it's timer/ thermostat kicks in? Or is the RCB too sensitive?
Please help!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 25 Jun 2009 00:04:55 -0700 (PDT), Bear wrote:

You use the abbriviation "RCB", I'm not sure what you *exactly* mean by that. A consumer unit can contain three different types of breaker (excluding the main switch...).
Minature Circuit Breakers (MCB) for each individual circuit (socket rings, lights, cookers etc), this provides overload protection only. This just has a toggle to reset it.
Resdiual Current Device (RCD) which monitors the live ane neutral wires and trips whne there is more than the specified current going than is coming back. No overload protection just dection of "earth leakage". This will have a "test" button and toggle to reset.
Residual Current Breaker Oveload (RCBO) these combine the function of an MCB and RCD into a single unit and provides both earth leakage and overload protection to the circuit passing through it. Again test button and reset toggle.
We need to know exactly what type of device is tripping.
--
Cheers
Dave.




Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

It gets worse if you have an old Voltage operated Earth Leakage Circuit Breaker :-(
Taking a giant leap of faith and assuming you have either an RCBO or a separate RCD serving the socket circuit(s) only then it is possible to test your RCD using an RCD tester which will check the operating current and time of operation. Also assuming the problem is down to leakage currents rather than fault (milliamps not hundreds of amps) There are other possible causes such as dampness/condensation ocurring under certain weather conditions or having a kettle blowing steam into a socket outlet above a worktop. Insects/small mammals can give rise to such a problem also. If you have the test equipment and the knowledge you can test the insulation values of the circuit and subject to vulnerability the apparatus you have plugged in. Some indication of your skill level would help but I can't help thinking that if you have to ask you may not be able to meet the requirements of testing the system and you really need a decent electrician to find the fault.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks for the replies.
My skill level is reasonable competence with electrics but anything which requires testing beyond a standard digital meter or common sense, I leave to the experts. I think the device is an RCCB (is this the same as an RCBO?). Indeed the smaller switches are MCBs, and there is a main master switch on the consumer unit. I also considered the option of dampness - but ripping the kitchen apart (where it's most likely to come from) is not a viable option. If it is dampness then I should be able to determine this by investigating the electrical sockets inside the kitchen - it has to get in somewhere!
When tripped, the MCBs remain in place - only the RCCB trips. My next course of action is to try the test button (duh - I know I should've tried this before posting) to make sure the RCCB is working correctly. Then I will systematically go through the MCBs to see if there is one where I have nothing powered which I can turn off. That will isolate one more part of the house to narrow down the problem. Also, I am trying to source some power breakers which shut off at 20ms or below. I read that consumer units are usually 30ms. I can plug these into the suspect devices and hopefully they will then trip (if faulty) before the consumer unit.
Perseverance.....
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
xxxxxxxxx
Also, I am

cpc farnell have some 10ma rcds which work at about 13 amps - i use them for my extension leads to the garden, as they should trip first...
[g]
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
george (dicegeorge) coughed up some electrons that declared:

Nice idea - but unfortunately it's not a given.
Once a fault >30mA has been seen by both devices, both will trip, unless one of them has an integeral time delay (Type S).
However, your theory works for fault currents between 10 and 30mA given or take device tolerances.
Cheers
Tim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A 3mA RCD should trip within 10% of the rated triping current so it might open at 27mA. It should not trip at 50% of the rated trip current so it should remain on at 15mA. There are other conditions to be satisfied but these are your two applicable ones. A multi-meter is unlikely to be able to be of help in finding a high resistance fault and I suggest you would need a Megger. I suppose I return to my original response that you need assistance or you might like to invest in an all-in-one multifunction installation tester which can carry our insulation, continuity,loop impedance, RCD operation and timing and other tests depending on the price you pay.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
cynic wrote:

ITYM a 30mA RCD
Andy
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In article

Right. So a split load CU fitted with a RCD - residual current device - to protect one group of circuits? This looks at the current flow on both line and neutral, and if they differ by more than the amount the device says it trips. Basically you have a 'leak' from either line or neutral to earth. And it's additive with appliances. Many will have 'bleed' resistors etc from line to earth for RFI suppression purposes. But only cause a tiny current to flow. Other likely ones are things with a heater of some sort - the mineral insulation inside a 'black' heating element can cause exactly this if it gets damp - but not enough to overload the circuit. Washing machines and immersion heaters are examples of this.
Turning of an MCB doesn't totally isolate the circuit as it only switches the line - and a neutral to earth fault will still cause the RCD to trip.
You need to *unplug* everything on the RCD protected circuits first. Pain with fridges and freezers, but you have to find out what is causing the problem. It's pretty unlikely to be the actual wiring unless bodged.
Things like immersions, showers and coolers have normally double pole isolation switching so can just be turned off. Of course if your sockets are new and of good quality they're likely DP switched too.
--
*Just give me chocolate and nobody gets hurt

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bear wrote:

Would I be right in assuming that it is the RCD feeding a number of otherwise separate circuits that is tripping?
See:
http://wiki.diyfaq.org.uk/index.php?title=RCD
for details of RCDs
If so, then the section on nuisance trips may help:
http://wiki.diyfaq.org.uk/index.php?title=RCD#Nuisance_trips
--
Cheers,

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bear wrote:

i once found a fault due to someone putting tin foil in a 13 amp plug to hold in the little screws, it was not enough to blow the fuse but enough to give me a shock (there was no rcd) so your problem could be a mouse half chewed through a cable.. not sure how you'd test for this...
[g]
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Oh what fun, not. Some things to keep in mind:
1. If you have an RCD then in some situations it can trip for faults between N and E. This happens when there is a small resistance on the fixed N wiring so a small voltage is present, especially when the circuit is loaded. If anything than connects N and E enough current flows to trip the MCB.
2. The individual MCB switches in the consumer unit only break the L wire, they leave the N (and obviously the E) connected so turning a circuit off individually does not isolate it for the purposes of eliminating it as the cause if the problem happens to be an N to E short.
3. Decaying vermin have a variable resistance. The one which got electrocuted between the L and E in our consumer unit caused tripping in much the way you have described.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks all for your thoughts. Yes the RCB does feed a number of other circuits and as for decaying vermin - the thought had occurred to me. But like others I would have no idea where to start testing for such things (assuming it is not obvious from a reconnaissance of the attic). Thanks John for the links - I will check them out
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bear wrote:

The wiki article includes most of our (i.e. uk.d-i-y as a group) accumulated wisdom on tracking down nuisance trips - so its probable a good starting point and covers much of the advice we would normally post in situations like this.
There is a fair amount of deduction you can do without specialist equipment - although it can be tedious!
--
Cheers,

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bear wrote:

Not true.
Any device that DOES draw power anywhere near a neutral<>earth short will trip one.
I have the same problem more or less isolated to one ring thats been extended..anything on a section that one trips the house.
I must get down to fixing it..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Ok - more information: Consumer unit is a Crabtree Starbreaker. The RCCB (labelled as such) is split load 63A/30ma (363/S030). The 3 MCBs it protects are 2x 61/ B32 MCBs and 1x 61/B20. The latter is for the extractor fan only. The other 2 - 1 is for all of the sockets except the kitchen, the other is the kitchen. I've pulled a few sockets apart tonight in the kitchen but all connections are tight and no signs of problems; except the freezer. The live connection wasn't tight and there's a small nick in the wire which could have connected to the securing screw for the socket. Doubt this is an issue though.
Next steps - source an earth leak tester cheap on the net and test all sockets. At the weekend scour the attic for dead/decaying vermin which may have chewed a cable (beginning to seem like the most applicable option).
One thing still puzzles me - 2 nights ago it tripped minutes after boiling a full kettle. Same thing happened when trying this process 5 minutes later. Eventually plugging in the kettle just tripped the sockets (as soon as the kettle was placed on its base) repeatedly - even tried sockets in the living room. Hence replaced kettle following day. That morning tripped around 1am.
I've moved the kettle away from the combi boiler - maybe the steam was getting inside unseen?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bear wrote:

perhaps having the kettle on drew a lot of power (13 amps) which warmed the wires up and the leakage increased due to the heat...
if it's like here sometime the kettle socket has an extension lead with 2 kettles, 2 toasters, a microwave etc...
[g]
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 25 Jun 2009 13:21:50 -0700 (PDT), Bear wrote:

You have found a "fault" though and presumably corrected it. I'd be tempted to wait a while and see if the problem has gone away but having found one socket with a loose wire and knicked insulation I'd be going round all the other accessories in the place, ceiling roses included.
--
Cheers
Dave.




Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Ok - more information: Consumer unit is a Crabtree Starbreaker. The RCCB (labelled as such) is split load 63A/30ma (363/S030). The 3 MCBs it protects are 2x 61/ B32 MCBs and 1x 61/B20. The latter is for the extractor fan only. The other 2 - 1 is for all of the sockets except the kitchen, the other is the kitchen. I've pulled a few sockets apart tonight in the kitchen but all connections are tight and no signs of problems; except the freezer. The live connection wasn't tight and there's a small nick in the wire which could have connected to the securing screw for the socket. Doubt this is an issue though.
Next steps - source an earth leak tester cheap on the net and test all sockets. At the weekend scour the attic for dead/decaying vermin which may have chewed a cable (beginning to seem like the most applicable option).
One thing still puzzles me - 2 nights ago it tripped minutes after boiling a full kettle. Same thing happened when trying this process 5 minutes later. Eventually plugging in the kettle just tripped the sockets (as soon as the kettle was placed on its base) repeatedly - even tried sockets in the living room. Hence replaced kettle following day. That morning tripped around 1am.
I've moved the kettle away from the combi boiler - maybe the steam was getting inside unseen?
I would not call small nick in a cable insignificant. I have discovered that to be the most common fault of RCDs tripping.
When trying to find faults like this it is worth remembering that extra loads (and that includes loads on the non RCD side of the board) can make the RCD more liable to trip if it is a neutral earth fault.
Before buying a tester you might be better off checking behind every socket in the house (you have found one potential fault) and seeing how things run for a while.
Adam
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
ARWadsworth wrote:

We got a split load board after a neutral to earth fault lost us all power until it was traced. Problem with neutral earth faults is that switching off individual circuits does not help to isolate the cause.
I would guess there is an underlying problem which puts the system on the edge all the time. Is it the same side of the CU that trips every time? If so trip could be super sensitive. Can substitution be tried? Can the trip be reset first time immediately after it trips? I would not have thought this likely if the cause was very obvious transitory damp.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.