There I was, minding my own business when 'click' all the power went off in the room. I only had a side light on at the time so thought it could have been a power cut. Went to the hall and found the light on so realised it was just my power ccts. Reset the RCD and it tripped again. Switched off all the MCB's, reset the RCD and turned the MCB's back on one at a time .. upstairs ring .. 'click'. I then removed all plugs from the ring and RCD reset ok. Plugging things back in found the washing machine (there is a little utility area also on upstairs ring) was the cause (but only when switched on at the socket to it's a live earth fault?)
So, what is likely to be the cause of a washing machine tripping the power when it's not actually turned on itself (ie what's between the plug and the main switch in the machine .. It's an AEG OKO-Lavamat
6100 Digitronic if that makes any difference?)
I'll pull it out and have a look tomorrow but I fancied some pointers meantime?
Depends on if your socket has a double pole switch or not... ;-)
Input filter as others said, or possibly water seeping into some place it should not (which would suggest an internal leak!). Any puddles under the machine when you move it?
Std MK double switched socket .. single pole? And if it is only single pole that pins it down to a live earth fault though eh?).
Are you all talking one of the inline sealed jobbys here .. L & N in and out, common Gnd (like you sometimes get built into IEC chassis sockets?
or possibly water seeping into some place
I'll let you know tomorrow ;-) Theres no 'visible' water leak as yet (it *has* leaked in the past .. I changed the drum bearings / seal and the water pump, both a few years ago now ..) and the drain backed up once (used the drain wand on my pressure washer). ;-)
It was working perfectly last night and wasn't on when it tripped the cct?
Will I need some 'special' gear for that .. only got a DMM?
If it only trips when I turn the thing on at the socket (ie netural and earth would be connected all the time) would that suggest the neutral earth leakage was ok (or below the trip current at least?)
That leakage is quite awkward to measure, its that sometimes if theres a short between neutral and earth some current needs to flow before it will show up. Bit late to explain all the niceties about RCD's.
And it actually trips the RCD, or just the MCB for that circuit. If it's the whole house RCD then it's a fault from live to earth through a cable or loose connection somewhere. Or the mains RFI filter on the appliance as others have already said. A fault to earth through the negative conductor will only show when the supply to the appliance is actually being used. That's the nature of un-balanced current flow in both conductors. Earth and negative are usually at the same, or bloody close to the same, potential while the appliance is lying dormant. But this being a washing machine supply, then look for water as well as burn marks on the wires inside. Mice can also chew through the flex in the most inconceivable places.
On Sat, 15 Jan 2005 00:10:15 GMT, "BigWallop" strung together this:
Nope.
Possibly.
Not always. It doesn't take much to knock the RCD out while other circuits are on load if there is a slight difference between N and E and there is a bit of a N\E fault somewhere..
*ignore all this and carry on following the advice from elsewhere in the thread. *
BW, you can have absolutely nothing pulling a load through an RCD and a NEUTRAL (not negative, that's DC), to earth fault *can* trip it.
Well, I'm sorry too, because I can't find anything, anywhere, that says a standard RCD in a normal domestic installation will trip the supply unless there is a fault from Phase to Earth. If the appliance is open circuit, all switches open, then the phase should not be connected to neutral through any load, and so this can't cause an imbalance in the phase to neutral loop which the RCD is there to detect. So, for arguments sake, we'll say that neutral and earth are in the same potential state. The phase is at higher potential than both neutral and earth. Phase and neutral are "not" connected through any load (open circuit). A straight short occurs between a neutral and an earth conductor. What happens at the RCD?
Therefore, the fault must lie between phase and earth for the RCD to trip the supply, because neutral is already at, or so close to, earth potential that the RCD will not detect any difference on this side of the supply. This would only happen if there was a closed circuit between phase and neutral, and a neutral conductor passed a fault current to earth at such a low impedance, which should be highly unlikely because neutral is already, or very nearly, at earth potential.
How I was told and read how it all worked was like this. The conductors and loads in a circuit act as resistance to the passage of electrical current. Placing two resistances in series only increases the total resistance in the circuit. But, if two resistors are placed in parallel to each other, the total resistance is actually reduced by a tangible amount in the whole circuit because the electrical current has two paths to flow through on that part of the circuit rather than just one. This reduction in total resistance in the circuit by placing a parallel resistor in it is what creates the imbalance for the RCD to detect. The RCD should only have one conductor with current going out and one conductor with current coming in. By making two conductors send current out, and still have only one conductor sending current in, the circuit becomes unbalanced.
That's why I always thought an RCD was placed in line to prevent shock or damage from an imbalance on the phase to earth side of the supply, not on the neutral to earth side of the supply as well. An RCD should also give no detection of a fault across phase and neutral because such a fault would also be detected as a balanced load across them. Reading the IEE and RCD manufacturers literature would also point me to believe this is true.
Yes you can have a slight increase in potential through heavy loading on other parts of the same neutral path, but these should never be enough to create a dangerous situation for the RCD to detect and trip open because earth should also be induced by these same small increases in potential that are effecting the neutral paths. So what you are saying is that the neutral or earth of the OP's supply are not operating properly to remove the unlikely event of a low resistance current flow between neutral and earth, while the neutral conductor is being induced by some other loadings on the same part of the circuit. This would cause the neutral to have a much higher potential than earth, and so would cause an imbalance for the RCD to detect. So do you think the OP should also have the supply and wiring tested to be sure that the safety devices fitted are going to properly protect from the potential harm of an electric shock?
(BTW, I use the word "negative" for circuit descriptions nearly every day and I was wrong to use it here as we're talking AC not DC, but old habits die hard. My apologies)
Not sure this helps anything but when I was rewiring Dads garage a while back I fitted one of those little RCD + 2 x MCB CU's.
I had powered it all up and was using the 'lighting' CCT and had the live switched out on the MCB. I cut through the T&E on the 'Power' cct and the RCD tripped (because the RCD had detected earth current derived from the neutral potential as they were shorted by my cutters?).
I wonder if the different devices work differently? I'm aware of ELCB's and RCD's (the RCD.s with MCB's built in are the same thing) and I think there was something before ELCB?
Earth and
Wouldn't that also depend of / if other devices are also running on that (or other rings) from the same RCD? That device may be off but beside it is say the tumble dryer pulling a few amps ...? With the washer plugged in (but turned off at the wall) and assuming the sockets only switch the live then the neutral / earth will still be continued into the washer and a 'fault' between them still detected?
But this being a washing machine
I'll look for that later today .. ;-(
Mice
Well, I'm not aware we have any mickys in here at the moment (we have had a few years ago .. came in from under the communial suspended ground floor .. holes now all filled .. ), I'll look for PVC chippings as well then ;-)
I don't think that is correct and in fact we have had an RCD trip caused by an electric kettle. Both the wall and kettle switches were Off and it required the kettle to be unplugged to stop the tripping.
An RCD trip from an N-E short is quite possible in this house when you look at the sums. We are on a two-wire supply from a transformer that is a few hundred yards away. Neutral is connected to Earth at that transformer. The N-E resistance measured at our house is 33 ohms, and is a measure of the resistance of that few hundred yards of clay soil, between our Earth rod and the Earth rod at the transformer.
Our N-E voltage, measured at the house, averages 0.7Vrms. This is probably due to the loadings of the five other houses upstream of us.
I= V/R, so an N-E short would result in 0.7/33 (21mArms) of unbalance current through the RCD.... even when there is nothing connected to the Line wire through the RCD.
If the N-E voltage or the ground resistance varies (long hot summers?), then the RCD unbalance current (and the chance of an RCD trip) would also vary.
Well I certainly managed to trip the RCD in my sisters house while working on a disconnected ring main. I put it down to the fact that the MCB only isolates the live and the neutrals are all linked thus a neutral/earth short anywhere on the system will give an alternative return path for any device drawing current.
A common question here goes along the lines of "I isolated the circuit at the fuse/MCB to do some work on it and when I cut a cable the RCD tripped. Why?" Answer: because you created a neutral-earth (strictly neutral-CPC) short with your wire cutters.
But there are always other loads to think about. These are passing current through neutral conductors somewhere. A N-E short creates an opportunity for the neutral current to take two parallel paths, one of which is through your RCD. The RCD then sees current in the neutral but not the phase(s); if this exceeds the threshold the RCD will oblige by tripping.
It probably trips. As soon as you short the neutral to earth the neutral is no longer isolated -- unless its isolated upstream at an all-pole isolator (not usually the case unless you've opened the main switch) -- current can now flow in the neutral and trip the RCD.
"At or so close to earth potential" is missing the point. It's easier to think about where current is flowing, and how it will be shared if there are parallel paths. If you want to think in terms of voltage though, consider the fact that you've got low impedances (copper wires) and that 30mA (or whatever) to trip an RCD is not much current. If the neutral is, say, only 0.1 volt 'above' earth then a N-E fault loop impedance of 3 ohms will cause over 30mA of residual current and trip the RCD. Typical Z-E shorts in domestic wiring will have a loop impedance of well under that. Even with the fault on the end of 50 metres of 1 mm^2 T&E cable you'd see under 2 ohms.
I hope you can now see the flaw in that argument. It's not highly unlikely at all; it's highly likely.
The type of earthing of the installation makes a difference. Let's work through the 3 usual cases:
TN-S (earth comes via supplier's cable sheath)
------------------------------------------------- Here there is always a voltage difference between N and E -- even if
*everything* in your house is switched off. This is because other consumers' loads are causing a voltage drop in the supply cable neutral between the point where your service cable is connected and the earthed point at the transformer. A N-E short in the house diverts a little bit of their neutral current through your neutral, your RCD and back to the transformer via the cable sheath. The RCD will almost always trip in these circumstances.
TN-C-S (PME)
--------------- Here your earth comes from the supply neutral entering the premises. If there are no loads on in your house there is no neutral current to divert and the RCD will not trip on a N-E short.
However if you are working on one RCD protected circuit (with its phase isolated) and there's load current flowing in another circuit protected by the same RCD, a N-E short in the circuit you're working on will divert some of the other circuit's load current through the earth, causing an imbalance and tripping the RCD.
TT (no supplier earth, own earth rod)
---------------------------------------- This is essentially the same as the TN-S case, except that the impedance of the parallel earth path is much higher and the risk of tripping somewhat lower. Nevertheless if your earth electrode is good and the incoming neutral is a volt or two above the local ground (again because of other people's loads) then a N-E short will trip the RCD -- e.g. neutral 1 volt above earth, earth electrode resistance 30 ohms (neglect other impedances): residual current = 33 mA, so a 30mA RCD will trip but a 100mA one won't trip.
BTW-1: RCD tripping on a N-E short is a Good Thing because it alerts you to the presence of a potentially dangerous problem. Neutrals and earths are not fused. If there's a parallel path and the main desired neutral path happens to go o/c then lots of load current could end up going through a bit of 1 mm^2 wire in your house, which might respond by catching fire...
BTW-2: None of this is relevant to the original subject of this thread. From the original article we know that the washing m/c does not trip the RCD when plugged in with the circuit MCB open. Therefore a N-E short can be ruled out and phase-earth leakage is the problem. Probably the EMI filter, or water leakage, as someone said a while ago.
On Sat, 15 Jan 2005 04:55:43 GMT, "BigWallop" strung together this:
An RCD doesn't trip on an earth fault as such, it measures the current in the phase and neutral conductors and if they are not equal, (to within the rating of the RCDs trip current), then it will trip.
But they might not be, let's say for arguments sake there isn't a fault, what does that prove?
Nothing, there has to be potential between the N and E for the RCD to trip, like I've said.
It appears that you haven't understood the workings of an RCD glasshopper!
An RCD detects an imbalance between the current leaving on the phase conductors and the current returning on the neutral conductor. They don't measure earth to detect a fault.
As you are basing your whole argument on your incorrect understanding of the function of RCDs then I'll let you try again, but with the correct answer!
No it didn't, it detected induced current through what should have been a neutral conductor, but which was then a phase conductor because the lighting was still in use when you cut the cable to the socket circuit. I can bet that the lighting and power cables run along side each other on some stretch of the wiring plan, and it was either the induced current, even though very small, or a larger impedance on the earth conductors that caused the RCD to trip open. It could have either been the earth was not properly conducting the residual current away from the induced leakage through the cable insulation, and this created a higher potential in the neutral conductor, or what should have been a neutral conductor had risen more toward phase potential from some other means as yet undiscovered. This would cause a Residual Current Devices to detect an imbalance between phase and earth and activate the breaker circuitry.
If you have a look at the inner workings of an RCD you see there is no way that a neutral to earth leak will cause the device to trip open. That's unless there is an earth loop impedance fault or, to put it another way, a higher resistance path on the earth conductors than the neutral conductors, which will then causes the neutral path to become higher in potential energy than earth and so cause an imbalance between a positive potential and negative potential at earth (where common current flow specific is used). This type of fault causes what should be a neutral potential to literally become phase potential and so again cause an imbalance between phase potential and earth potential which an RCD is designed to detect. Here:
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for instance, shows how the device works, with a diagram of the inner parts.
The whole point of equipotential bonding using larger cross sectional area (csa') conductors than those used in the supply, is to greatly reduce the impedance along these conductors. The reduction in impedance should be to such a level that will not cause what should be a neutral potential to obtain phase potential. This use of large csa' cables for earth bonding should be capable of removing all residual current obtained by the neutral paths, either through inductance or contact with a phase potential conductor, and should also be capable of preventing the neutral path from creating an imbalanced current flow between it and earth. Neutral and earth should always remain at the same potential, or at a very negligible measure from it, no matter where it is on the whole installation plan. This is the requirement, stated in all the good guideline hand books and other literature, for the earth bonding to have proper residual current removal properties.
An example. Phase and neutral conductors can be created using, lets say,
2.5 mm csa' conductors but, to remove the residual current created by close proximity between the two supply conductors and any other means of induced current flow, the earth bonding conductor needs to be of a larger csa', of more commonly 4 mm to 6 mm, to reduce its impedance further than the supply conductors and so be capable of reducing induced current flow and prevent nuisance trips on an RCD. So, larger cross sectional area cables are used for equipotential bonding to produce a much lower impedance path to ensure proper earth leakage current detection from the phase supply. This, in turn, creates a much safer reaction time if such a leak to earth does occur. It isn't just a small safety thing to use equipotential bonding, it is also there to keep both phase and neutral paths in balance so that a higher residual current, commonly 30mA, can be detected quickly.
It is natural to have a current flow of anything up to 12 mA, or even 15 mA in some installations, between phase and earth/neutral conductors, even when they are not under load. This is due mainly to induction through their close proximity with each other inside the insulated outer sleeve of the cable. The totally bare earth protective conductor is placed in the cable to try to reduce this natural induced current flow phenomenon as much as possible. The bare conductor should also help bring the two supply conductors back in to a balanced state again. It isn't because the cable makers are stingy with the insulation materials that the earth protective conductor is left totally bare naked, it's because an insulated coating would create a much higher resistance and reduce the bare conductors capabilities in removing the residual current and so be unable to creating some kind of harmony inside the cable again. Electricity suppliers also use tests to make sure that the earth bonding at a supply is within certain limits. This is to create a proper equipotential bond between all the conductors. To high an impedance on any one of them, phase, neutral or earth, will put the whole power balance out of sync and cause problems.
So, to sum up, I still say an RCD will not trip open unless the fault current it detects is between a phase potential and earth mass.
Boy, can I go on a bit when I get started. :-) LOL !!!
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