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joebre
Junior Member
Joined: 08 Oct 2008
Posts: 13
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 Posted: Wed Oct 08, 2008 5:29 pm Post subject: RCD trips but can't find fault ! |
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In new house and still on snag list.
Something is causing the RCD to trip and the electrician in not being helpful.
The RCD trips and no MCB goes down.
Most times, the RCD will go back up but sometimes I have to push it up 5 or 6 times.
By trial and error, I have narrowed it down to an MCB in the kitchen area containing steam ovem, warming drawer, mircowave and coffee machine.
I am plugging out these appliances, one at a time to see if I can narrow it down.
Is there some test that I can ask the elec trician to carry out.
Many thanks,
Joe
Last edited by joebre on Wed Oct 08, 2008 5:56 pm; edited 1 time in total |
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IDontBelieveIt
Senior Member
Joined: 29 Jul 2008
Posts: 940
Location: North Hampshire
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| Posted: Wed Oct 08, 2008 5:44 pm Post subject: |
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ECLB were used years ago and not any more - I think that you mean RCD.
An RCD trips when there is a leakage from either or both the live and/or neutral conductor to earth. Indeed a Residual Current Device does just that it 'checks' any residual current as the current in the live and neutral circuits should be the same at all times, if not then there is a leakage and typically, and probably in your case, this will be a leakage of 20 mA (0.030 amps). A leakage could be caused by YOUR finger on either live or neutral hence they are nifty devices as and RCD trips much faster than an MCB.
And so back to your problem. Other things that can cause an RCD to trip are things with heating elements within them (ovens, electric hobs, irons, etc)
Pound to a Penny it is one of these appliances causing it.
Any decent elecrician will have an RCD tester and able to test that the RCD is functioning properly.
If it is not an appliance then we move onto other things and this is where you should star to worry - another cause is a breakdown in the insulation of the house wiring and this can result in having the house rewired. As the house is 'new' then this is most unlikely to be the case. But may be of interest to other readers with like problems.
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joebre
Junior Member
Joined: 08 Oct 2008
Posts: 13
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| Posted: Wed Oct 08, 2008 6:08 pm Post subject: |
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Post title changed, thanks.
You can see I have limmited electricial knowledge !
What is strange about the tripping is that it can happen when we are out of the house. That rules out the microwave, steam oven and warming drawer. The coffee machine goes into standby most of the time as well, but it may trip when coming out of standby ?
It could trip three times in one day and then not trip for a week !
I have posted another query in the Lighting section so you can see that I am not happy with some of the work ! |
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joebre
Junior Member
Joined: 08 Oct 2008
Posts: 13
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| Posted: Thu Oct 16, 2008 8:39 pm Post subject: |
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As follow on to my first post, I thought the fault was in the kitchen. I turned of the appliances, one at a time, over several days. Eventually all appliances were off and the RCD tripped again. So that rules out that block of appliances.
Wondering what will an RCD tester do ?
Will it test the RCD's in the board or is there a test of each of the individual sockets throughout the house.
Thanks for reading
joebre |
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Rich-Ando
Approved Electrician
Joined: 24 Mar 2007
Posts: 2483
Location: Derby, Derbyshire
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| Posted: Fri Oct 17, 2008 1:13 am Post subject: |
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unless your board is a 17th edition one it will more than likely only have one RCD in the board.
the tester will just prove the function of it.
if you have unplugged everything and it still does it then the chances are it is now a wiring side fault. do you have any external sockets? i ask only to rule out moisture tracking across the terminals.
this kind of fault is one of the hardest to find. intermittent ones always are.  |
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IDontBelieveIt
Senior Member
Joined: 29 Jul 2008
Posts: 940
Location: North Hampshire
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| Posted: Fri Oct 17, 2008 7:19 am Post subject: |
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As Rich says an RCD tester will only test functionality, there is a possibility that the when testing it may reveal an overly sensitive RCD (example its a 30mA sense RCD and it is tripping at 5mA, say). Were that to be the case it would be a first for me as I have never come across one yet.
Also as Rich says any cables of any type going outside (to sockets)?
Also as Rich says (  ) finding faults like this are one of the hardest and most tedious, with a locating a broken ring a close second!
As I assume that you do not have the test equipment (RCD tester and insulation tester) it is gong to have to be a trail and error process. 
It is also going to be pain in the neck for the family.
1. Turn of each MCB (or remove fuse) in turn, leave for along period (without having use of that circuit) and see if RCD trips.
2. Having done 1 to ALL circuits that are protected by the RCD and if the RCD continues to trip then the fault is almost certainly with a neutral.
3. Now you have to be careful of competent and [color=red]do take great care please inside the consumer unit[/color]. Turn off power. For each circuit protected by the RCD turn off the RCD (remove fuse) then remove the neutral from the neutral bar for the same circuit. Again wait a while with the use of that circuit. Re-instate the neutral turn back on RCD and proceed to next circuit and do the same.
4. If that does not find which circuit is at fault then call in an electrician (or do that now).
By the way has anyone been adding to or making any changes to the consumer unit recently (and wires moved, deleted or added)?
And final 'by the way' are there any large electrical consuming companies near by to you (factories) etc
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joebre
Junior Member
Joined: 08 Oct 2008
Posts: 13
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| Posted: Fri Oct 17, 2008 7:45 pm Post subject: |
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Thanks lads for your advice.
Came home last night and my outside lights were off. Temporary measure of 2 LV transformers plugged into an extension lead. Lead covered in plastic but suppose there is a chance of dampness ?
Went inside and the RCD would not reset. Turned off the MCB covering that area of kitchen that I described in first post. Reset RCD. Went to kitchen and found that all the devices on that MCB were switched off at sockets. None were plugged out.
Went and reset MCB and RCD tripped again.
While I am prepared to try some investigation, can you tell me if RCD can trip if devices are plugged in but switched off.
Outside lights are on separate MCB.
There are no factories or high users near me.
Thanks again !
Joe |
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IDontBelieveIt
Senior Member
Joined: 29 Jul 2008
Posts: 940
Location: North Hampshire
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| Posted: Sat Oct 18, 2008 6:31 am Post subject: |
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Oh yes RCD's can trip even if appliances are plugged into a socket that is switched 'off'.
And the reason for that is that RCD sense an imbalance in current flow in live and neutral conductors (both should be the same). Sockets when 'off' are single pole switches - they only isolate the live conductor.
And my friend that is a good sign that the problem is probably on the neutral side of things and unlike the live conductor the neutral conductor is common to ALL circuits protected by the RCD the live conductor has an MCB/fuse allowing it to be isolated from the RCD, the neutral is never isolated from the RCD - of you get my drift.
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joebre
Junior Member
Joined: 08 Oct 2008
Posts: 13
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| Posted: Sat Oct 18, 2008 11:44 am Post subject: |
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Thanks, that explaination helps.
As you can imagine, the external lights are switched off at the wall but the extension lead is still outside and subject to dampness. I will plug that out now as part of the "trial & error"
What about the MCB that controls some of the kitchen appliances ?
While it does not trip itself, it needs to be switched off sometimes to allow the ELCB to be reset. Should I plug out those appliances as well ?
Many thanks,
Joe |
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IDontBelieveIt
Senior Member
Joined: 29 Jul 2008
Posts: 940
Location: North Hampshire
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| Posted: Sat Oct 18, 2008 12:18 pm Post subject: |
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| joebre wrote: |
What about the MCB that controls some of the kitchen appliances ?
While it does not trip itself, it needs to be switched off sometimes to allow the ELCB to be reset. Should I plug out those appliances as well ?
Joe |
Well that statement has just thrown my other theory out of the window!!
An MCB only trips when the circuit that it protects takes more current than the MCB is rated to trip. So a 32A MCB will trip if the current flow through it exceeds 32 amps ('ish)
If the RCD (NOT an ELCB they are ancient old things and if it IS an ECLB that that needs to be ditched and replaced by an RCD for starters!) will not reset at ALL unless that MCB is switched off then it IS an appliance OR the circuit insulation is breaking down! And here we go again!
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joebre
Junior Member
Joined: 08 Oct 2008
Posts: 13
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| Posted: Sat Oct 18, 2008 12:38 pm Post subject: |
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Sorry to confuse, IBDI
I keep saying ELCB when I mean to say RCD.
Joe |
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joebre
Junior Member
Joined: 08 Oct 2008
Posts: 13
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| Posted: Thu Nov 27, 2008 12:00 am Post subject: |
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It was too good to be true !
As part of my trial error test, the outside lights were plugged out for the last 8 nights.
No problem at all.
Left house for an hour today and when I came back, the RCD had tripped. No one in house at the time.
Only devices on were laptop, fridge/freezer, separate fridge and a coffee machine. The coffee machine stays on for an hour after making a cup. I had a cup before I went out. I suspected it before as I had trouble a couple of times trying to reset the MCB that controlled the coffee machine
I will have to go back to the trial and error again or is there any test that I can have done?
Joe |
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