Tumble dryer tripping RCD

[StepOne]

Hi,

At the worst possible time (just back from a week's holiday with what feels like a month's worth of washing!) our tumble dryer has started tripping the RCD. The first time, it had been running for about 20 minutes. I reset the RCD and put the dryer back on, ten minutes later it tripped again. After the third time of this, the RCD would not reset until the tumble dryer was switched off at the wall.

That's the situation we are in just now - as soon as the tumble dryer is switched on at the wall socket, the thing trips. The dryer itself is not on at the time - the timer is set to zero.

I'm not sure what is what on the RCD - there is a bank of 5 switches controlling individual rings. Then a yellow 'test' button, then a black switch which turns off everything on that floor - it's that black switch that is tripping, not the individual 'sockets' circuit. (There's also a second set of those switches for the upper floor, and the master red switch none of which are affected)

I've opened the back and bottom panels of the dryer and hoovered out as much fluff as possible, and hair-dryered around any 'connector' type thing but it has made no difference. Googling suggested replacing the mains filter, but I'm not even sure where that is on our dryer. It's a Bosch Classixx vented (i.e. not condensing) type. We inherited it when we moved in a couple of years ago, but I don't think it was that old then, so I would have hoped to get a few more years out of it.

Does anyone have any suggestions on what I can try next?

Thanks,
StepOne

[Itsallaguess]

Does anyone have any suggestions on what I can try next?

First thing I'd do is to isolate the heating element properly, and then try the dryer as normal, with the RCD reset to check it doesn't trip.

With the heating element isolated, if it doesn't trip again and the dryer operates as normal, minus the heat output of course, then swapping out a replacement element might be required, but you should at least be able to isolate the problem if this is the case.

I seem to remember on the Bosch Classix the rear panel comes off and you can access the heating element through there.

Usual safety warning apply. Don't attempt this if you don't know what you're doing....

Cheers,

Itsallaguess

[pendas]

As the previous poster suggested, isolating in turn the heating element and the drum motor may point to the culprit. If it trips with both of these isolated, there may be some mains filtering where the mains lead enters the machine and this would be suspect.

[csearle]

...After the third time of this, the RCD would not reset until the tumble dryer was switched off at the wall.

That's the situation we are in just now - as soon as the tumble dryer is switched on at the wall socket, the thing trips. The dryer itself is not on at the time - the timer is set to zero.

I'm not sure what is what on the RCD - there is a bank of 5 switches controlling individual rings. Then a yellow 'test' button, then a black switch which turns off everything on that floor - it's that black switch that is tripping, not the individual 'sockets' circuit. (There's also a second set of those switches for the upper floor, and the master red switch none of which are affected)...

...Does anyone have any suggestions on what I can try next?

Firstly the function of the RCD (Residual Current Device) is to detect an overly large leakage of current from line or neutral to Earth and disconnect the supply. The MCBs (Mini Circuit Breakers), which in your case are not tripping, detect overcurrents on individual circuits.

The switch on the wall only switches the line and not the neutral so, because this switch clears the fault, the leakage is from line to Earth.

As the tumble dryer causes the RCD to trip even when it is not heating the fault will probably not be in the heating element(s) or motor.

So that leaves the line conductor (almost always insulated brown these days) from and including the plug, down the lead and into the tumble dryer and up to the timer switch.

Usually these RCD trips are because of ingress of water into the electrics. So I would think carefully about water leaks - were there any possibly from other machines in the vicinity?

Another possiblity would be if there was some mechanical stress on the lead causing some kind of insulation breakdown, but the way you describe the fault developing makes this seem unlikely.

If there is a filter permanently wired to the mains input (usually to make the machine conform to requirements concerning the injection of harmonics etc. back on to the line from the motor etc. ) then this is also in the frame. (If it were me I'd try and locate it, temporarily disconnect it, and see if this cleared the fault in the not-tumble-drying-mode.)

Apply a warm blast of air from a hair-dryer to all the parts I've mentioned, including inside the plug if it's unscrewable - this might help if moisture remains somewhere.

Regards,
Chris

PS One quite rare potential scenario is that your tumble dryer is completely unchanged and has an (unchanged) designed-in leakage to Earth through the filter, and that another piece of equipment (most likely with water or oil in it) has develolped a moderate leakage to Earth, but of a size that doesn't trip the RCD. The effects of this leakage are additative, so the two devices together could push the RCD over its limit (usually set to 25mA). As I say, this is possible but not probable.

[StepOne]

Thanks for all replies.

I opened the back, and there were 4 pairs of pink connectors which appeared to be connected to heating elements. I disconnected one from each pair, and switched on at the wall, and it still tripped. I've not managed to get to the motor, which is a bit harder to access, but I do think it must be something else as the dryer is not actually on when it trips.

csearle - is the filter a capacitor? The brown and blue lines come in to the dryer, then both disappear into a connector, and come out the other side as two brown lines. Plugged into this connector is also a small grey capacitor (I think - the writing says MiFlex WXP-223m or something like that). Is this the filter? I'm not sure how I could disconnect it without cutting the wires?

There's been no obvious leak in that area, but the back wall of the utility room behind the dryer does look like it has suffered in the past - it's all flaking paint and crumbling plaster. I'll try the hairdryer tip, and plug the dryer into a different socket and see how I get on.

StepOne

[csearle]

csearle - is the filter a capacitor? The brown and blue lines come in to the dryer, then both disappear into a connector, and come out the other side as two brown lines. Plugged into this connector is also a small grey capacitor (I think - the writing says MiFlex WXP-223m or something like that). Is this the filter? I'm not sure how I could disconnect it without cutting the wires?

There's been no obvious leak in that area, but the back wall of the utility room behind the dryer does look like it has suffered in the past - it's all flaking paint and crumbling plaster. I'll try the hairdryer tip, and plug the dryer into a different socket and see how I get on.

The filter will have a capacitor as part of it, yes. I've Googled the number and it is frankly a tiny capacitance (close your ears communications engineers) so that is likely to be to do with RF emission suppression I think. Even if it were faulty the impression I'm getting from you is that this is connected across the mains input, which would not provoke the RCD to trip whatever fault it may develop.

The past is the past. For the RCD to trip it needs to be wet right now. If you experiment plugging the dryer into another socket then try it on the upper floor. The trick would be to get it on "another" RCD or, if we are talking urgent-drying-need then on a circuit without an RCD if at all if possible. But please be aware that an RCD tripping is protecting everyone like an early-warning-system so if you do get the dryer working on an unprotected circuit then keep an eye on it.

If you really do want to home in on it then you need to eliminate bits one stage at a time. So you could disconnect the lead from the dryer and test just the lead plugged in. (Keep children on a lead whilst doing this.)

Your advantage is that if the fault is solid, i.e. it trips the RCD consistently and fairly quickly you can home in on the cause by a series of disconnections.

Feel free to post your findings, sooner or later we should get there.

Regards,
Chris

[jfgw]

I opened the back, and there were 4 pairs of pink connectors which appeared to be connected to heating elements. I disconnected one from each pair, and switched on at the wall, and it still tripped.
StepOne

You need to completely disconnect the element to check for an earth fault. Make sure you know which lead goes where, then disconnect all of them and try again.

Some 13A sockets are double-pole switched (some MK ones are). Depending upon your earthing system, an earth to neutral fault can trip an rcd.

Use your eyes: check thoroughly for visible signs of damaged wires, burnt connectors and other potential earth faults. If the plug is a rewirable one, check that too.

Julian F. G. W.

[StepOne]

I disconnected the blue and brown wires from where they plugged into the capacitor i.e. just after they enter the body of the dryer. I plugged in and switched on and the RCD tripped. So it seems to be the plug (which is moulded). Does this sound likely. Is it worth cutting it off and replacing it? On close inspection of the plug there was what looked like a small blue colour discharge where the metal of the live prong emerged from the plastic of the plug.

StepOne

[StepOne]

Hi,

Curiosity got the better of me so I just went ahead and cut into the moulded plug. I certainly looked like it might be the cause of the problem - lots of discolouration on the metal. I've tried to take a picture - not sure if it will be viewable but here is a link.

https://1drv.ms/i/s!AlqP4Us57ye5gYYH9EG06LUPb0D3xw

That's the earth connector at the bottom of the picture. It's not clear on the picture but some of the plastic around the Neutral connection looked brown as though that had been discoloured as well.

Is it possible that this has built up over time, just because of damp air from the dryer? The socket is on the wall directly behind the dryer, below the work surface. Would it be worth getting an electrician in to look at this socket (it's a double socket with the dishwasher also plugged in there).

Also, is it safe to replace the plug with a standard 13 amp plug or is there a better option?

Thanks,
StepOne

[csearle]

Is it possible that this has built up over time, just because of damp air from the dryer? The socket is on the wall directly behind the dryer, below the work surface. Would it be worth getting an electrician in to look at this socket (it's a double socket with the dishwasher also plugged in there).

Also, is it safe to replace the plug with a standard 13 amp plug or is there a better option?

Looks highly suspect to me. Yes just wire on a replacement plug.

The socket outlet is only rated at 13A by the way so you shouldn't be using it for a tumble dryer and a dishwasher switched on at the same time. If you do it will be overloaded at times which, in my experience, very frequently has dire consequences.

Before paying for an electrician simply turn the socket off (you could do this using the RCD or the associated MCB), unscrew the two plate scerws holding the socket accessory in place and look behind it to see if anything looks amiss.

Regards,
Chris

[Sussexlad]

No, it's very unlikely to be anything to do with the tumble drier. Burning is caused by a bad connection, possibly in the plug but as likely to be in the socket. Yes, it perfectly OK to use a re-wireable plug but you need to also check and likely replace the socket as well, before using it again.

[csearle]

...but you need to also check and likely replace the socket as well, before using it again.

I agree, especially as the socket has probably been used overloaded for quite some time. They don't cost much to replace and it is a good DIY job, so nice and cheap. I'd also be thinking of adding an extra socket to the circuit at this stage so the machines can be plugged one into each.

Chris

[StepOne]

Update. I cut the plug off and replaced it with a wired one. The dryer went on again and ran for 30 minutes no problems. Success! And much cheaper than a new dryer.

We only got the dishwasher in February and it's​ probably only been on a dozen times or less so hopefully we have not been putting too much strain on the socket. For the time being I will keep the dryer plugged in to the sockets above the worktop and at some point i will check out the state of the problem socket.

Thanks to all for helping out

StepOne

[csearle]

Update....

Great.

[jfgw]

If there is any sign of burning on the plug, replace the socket as well otherwise the new plug may get damaged. Burnt plugs and sockets are like a sexually transmitted disease. If the dishwasher plug has been faithful to that socket, and if the socket has been faithful to that plug, the rest of the plugs and sockets in your house should be ok. A few transgressions can mean that there are other plugs and sockets that have become burnt. Vacuum cleaner plugs can have very loose morals and, if this has become burnt, you may find that several sockets around the house have become infected - I mean burnt - too.

Julian F. G. W.

[jfgw]

That verdigris doesn't look good. Is there any sign of dampness? Is the plug and socket near the tumble drier vent? Where does the drier vent to? Does it vent outside or into one of those plastic boxes?

Julian F. G. W.

[csearle]

Burnt plugs and sockets are like a sexually transmitted disease. If the dishwasher plug has been faithful to that socket, and if the socket has been faithful to that plug, the rest of the plugs and sockets in your house should be ok. A few transgressions can mean that there are other plugs and sockets that have become burnt. Vacuum cleaner plugs can have very loose morals and, if this has become burnt, you may find that several sockets around the house have become infected - I mean burnt - too.

Ha ha, ha ha, ha ha, brilliant!