The main RCD in our consumer unit seems to be very much on a 'hair trigger' and cuts out regularly, causing mayhem to pc users and dvd recorders!
We thought at first it was just when the heater in the washer/drier kicked in, but closer observation shows that it trips in various combinations of heating element devices like kettle/toaster/cooker/washer, tending most to cut out if two of these happen to be on at once.
Also light circuit RCD always trips when a light bulb goes, but main also trips if the light's earth is touched when removing lamp holders even when the lighting RCD is 'off'?
The consumer unit was fitted by a competent electrician and the problem was not immediately apparent after the fitting.
You really need to get an electrician in to do some proper diagnostics. Whilst RCD's can develop faults, my gut feeling is that you have some other problem.
The lighting MCB tripping when a lamp blows is quite normal though.
RCD's operate on the difference in current flow between what goes in on the live and what comes out via he neutral - the difference being what is leaking to earth. Enough leakage and they trip. Some of the leakage can be deliberate in the form of filters. PC's, monitors, printers and certain appliances etc. are fitted with filters on there mains input.
Sometimes the heating elements on kettles, washers and dishwashers can deteriorate and start to leak current to ground.
All of the above can cause nuisance tripping of RCD's.
Lacking an insulation tester, the best way is to note what was running at the time of the tripping and gradually work out the cause.
MCB's quite often trip when lamps suddenly burn out - they are very sensitive and fast to respond to over current, unlike a fuse. As a lamp burns out, it can strike up an internal arc which draws excess current, thus causing the MCB to trip.
The current imbalance that the RCD trips out at is additive - sounds like you have several small leakages which are very common with certain types of heating elements. Hence the common use of split load units that allow things like cookers and immersion heaters to be fed from the non RCD protected side.
An RCD works by measuring tiny current imbalance between neutral and earth. Short neutral to earth with the circuit switched off and you get a tiny current flow between those but not in the line. So the RCD trips.
Could be the 'leakage' of some appliances have increased since then.
There are devices available for this purpose. You might be able to hire one. But probably cheaper to just replace it on spec. But I doubt it's actually faulty.
Lighting RCD? or do you mean the MCB? An MCB tripping when a bulb blows is fairly common for the reasons already posted.
I don't quite follow what you mean. What do you mean by "the light's earth"? The metal body that the pins of a bayonet bulb twist and latch into or one of the power connections?
An MCB is a single pole device, the neutral is still connected to the circuit. Shorting neutral to earth can cause an RCD to trip as not all the current going to the load in the live is coming back through the RCD on the neutral, some is going via the short to earth. This sort of indicates a possible problem with the supplies neutral/earth bonding or with the earth conection.
But if you have a lot of devices with SMPSU's there could be a lot of "normal" earth leakage which will have the affect of making the RCD appear over sensitive. How many, PCs, printers, monitors, dvd and/or video machines, digi boxen, TVs etc are plugged in? They don't have to be powered on, just plugging in puts the filter components across the mains.
these things have been a pain in the arse for a long time. they trip out all the time. it is is easy to link them out and bypass, i have done this for many year and have no problem with tripping any more, do it and save you all the bother of lights out etc.
check the nomenclature to make sure we are not talking at cross purposes.
This could indicate that you have a faulty heater element in one or more of these devices. Alternatively you may just have too many devices / circuits protected by the device, and hence it is normally very close to its trip threshold.
Do you mean MCB here? If so that is not unusual - especially with mains halogen bulbs. In some cases replacing the MCB with a "Type C" MCB (normal ones are type B) can reduce this problem.
formatting link
you really do mean the RCD trips on a bulb failure then that is again an indication that the leakage current is nominally right on the trip threshold, and even the minuscule current imbalances that can result from the effects of surges and spikes on the supply are enough to push it over the edge.
They can fail, but it is not common.
Using a RCD tester is the easiest and most reliable way (especially ensuring that they are tripping fast enough). However there are other methods described in the RCD article above. See the section on nuisance trips.
I've yet to have a nuisance trip on my split load unit. If I had I'd investigate why.
However, the lighting circuits do sometimes trip their MCBs when a bulb blows. If this really is a concern they can be changed to ones which allow a longer 'instant' overload. Or arrange the wiring so the hall and stairs is on a separate circuit as I've done - that way a source of light is no further away then than the nearest door.
How much does residual current monitor RCM cost, from where?
They seem to have a readout of how much current is being lost to earth, so could be used to see which appliances are leaking how much (by turning them on and off) if an RCM was installed bedore the fuseboxes..
The only type I have seen are the very high sensitivity clamp meters, that you place around the phase and neutral to your appliance / circuit / whatever of interest. They then measure the (very small) imbalance if present.
Do you mean RCD or MCB? I guess RCD as you mention touching the earth. RCDs will trip if neutral / earth are accidentally connected. There is usually enough voltage.
The basis of an RCD is a current transformer carrying both live and neutral conductors. If there is a difference in current, sufficient voltage is developed to trip the circuit. There is little that can go wrong with the sensor but the trip circuit can fail which is why they should be tested regularly.
Check the circuits carefully before blaming the RCDs.
If you're after a Darwin award you could also try replacing those flimsy fuses with more robust chunks of solid copper and dispensing with earth conductors on your electrical system. Then, since your lights aren't likely to trip out, what's the point of having banisters around your stairs? Next to go those pesky smoke detectors. Don't forget to bypass those unreliable flame sensors etc on your boiler. In your car you can get rid of those irritating warning lights, not to mention those awkward seat belts, and so on ...
With RCDs As far as users are concerned, the single greatest problem with RCDs is nuisance tripping. This problem will either be due to the design of the RCD or due to the installation. Nuisance tripping can be a frustrating problem for the user and there have been cases where RCDs were strapped out, removed from installations completely or replaced with RCDs with a higher rated trip current. All of these types of actions are very dangerous and should be avoided. Where the problem lies with the RCD design, it is usually attributable to factors such as voltage spikes, surges, switching transients, noise, inrush currents, etc. Over recent years, the problem of nuisance tripping attributable to the RCD itself have been addressed by IEC. New tests have been introduced into the product standards to ensure that RCDs have a reasonably high immunity to nuisance tripping. Unfortunately, all RCDs do not comply with the new requirements. To minimise this problem, ensure as far as possible that the RCD has compliance to IEC61008 or EN61008 (RCCBs) or IEC61009 or EN61009 (RCBOs) and also to IEC61543 or EN61543 (EMC requirements for RCDs). To the top
Sometimes the problem of nuisance tripping is attributable to the installation. IEC recommend that the standing earth leakage current on the installation should not exceed 30% of the rated trip current of the RCD intended to be used on that installation. This means that for a 30mA RCD, the standing earth leakage current should not exceed 10mA. Given that a 30mA RCD may trip anywhere from 15 - 30mA, a 10mA standing leakage current will virtually prime the RCD to trip. In general, RCDs cannot tell the difference between a standing leakage current and an earth fault current. The sum of these two currents is the residual current seen by the RCD and if this aggregate current is greater than its rated trip current, the RCD will trip, unless it's faulty. (but that's another story) To the top
The problem of standing leakage currents is increasing. This is due to two factors:
1.. equipment manufacturers filtering internally generated noise to earth 2.. fitting of RFI suppression to provide immunity to mains borne noise. Recently introduced European Directives on EMC require manufacturers of products, appliances, equipment, etc. to contain within specified limits the levels of RFI type emissions produced by their products. Manufacturers often have to resort to the use of filtering circuits to meet these requirements. The filtering circuits can divert high frequency signals to earth, but can also result in the flow of significant levels of leakage current to earth at the standard 50Hz frequency. Under IEC rules, electrical appliances may allow a standing leakage current of up to 3.5mA/50Hz to flow to earth. Such current levels coupled with other sources of standing leakage currents can give rise to nuisance tripping. To the top
Washing machines, oil or gas burners and even immersion heaters can contribute to nuisance tripping. Temperature and humidity may also be factors in nuisance tripping. Other factors contributing to nuisance tripping may be poor earth terminations, surge suppressers, neutral voltage rising above earth potential, etc. A very sneaky problem is where an earth fault current on the supply side of the RCDs manages to appear as a load side fault to the RCD, causing it to trip. This problem is more usually associated with IT systems, or on TT systems with high earth impedance. Before changing the RCD in response to a nuisance tripping problem, check the installation by measuring the standing leakage current and carrying out an earth loop test. Also try to identify equipment that is likely to contribute to standing or transient earth currents. A residual current monitor can be fitted to an installation to detect the level of the standing earth leakage current or even transient leakage currents. To the top
Well! I have to say a big thankyou, and that I am very impressed with you all! Thankyou for this excellent lesson and references to all who contributed. I had not noticed there was even a Diy version of Wiki, and now it's been pointed out, perhaps I will not have to trouble you with so many silly questions in future.
Apologies for having been offline since asking the question, and for the confusion caused by lumping RCDs and MCBs together - most of you saw what I really meant, thanks.
It turns out that we had had two problems with elements at the same time. I had just replaced an oven element, that had been gradually failing and was only realised when it finally went completely open circuit.
After that replacement, I was anticipating a blissful end to the tripping, but then I realised, after following up complaints from the 'other half' that the washing machine was 'rubbish', that it had been washing in cold water, and probably for some time!
A clip had come adrift inside the drum and allowed the heater element to be rubbed down gradually, causing the leakage, but, subsequently, a damper strut had broken, and thrown a connector off the element, thus showing up as the 'cold water problem', and temporarily ending the tripping... Till I went to put the connector back on (not, at that stage, noticing the broken strut)!
I should have looked for this earth leakage problem before, but, as the washing machine element was fairly new, I had thought that was probably ok, and had not remembered about the clip that holds it away from the drum and what might happen if this were to break...
So, it looks like I was taking the RCD's name in vain, and it really is doing its job nicely (Though I do have a fair number of IT and video things about, so I will definitely bear in mind all of what has been said in this thread above in future).
So, now all I have to do is think of a way I might be able to retain a new washing machine element in place without having to strip every last thing out and split the drums, just for the sake of a little piece of stainless 'coathanger wire'. Drills and grommets come to mind, but that's for another thread or forum.
HomeOwnersHub website 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.