Unusual RCD tripping by tumble drier

[Jeff Layman]

Last year we had a problem with our 5-year old Beko tripping the RCD when it was turned on (NB it had been modified during a recall shortly after we bought it). It only did it on that one day and has been fine since.

A month ago it ran through its drying cycle with no problem, and beeped that it had finished. We removed the dry washing, and took it away. When we returned a couple of minutes later, we found the RCD had tripped. This has occurred twice again - the dryer is fine working, but trips the RCD as it cools down. Once cool, it seems ok and can be used again.

I'll have a look inside to see if there's anything obvious, but has anyone heard of a fault which behaves this way?

It may be time for a new drier, but I'm intrigued as to what this one is doing.

[Martin Brown]

I have seen this sort of fault the other way around with failing kettles where there is an initial RCD fail when used from cold but the thing will then work for a good while after you have reset the breaker.

Eventually it fails completely and never recovers.

My guess would be condensation getting somewhere that it can provide an earth leakage path.

Can you measure resistance (when unplugged) from live to earth and detect any difference in the failed state?

[Jeff Layman]

Yes, that could be it. But it would have to be pretty early on in the circuitry, as it still trips when the on-off push switch is "out". I guess it could just be a "false" physical break, and it's really an electronic circuit break which still leaves some connection even after switching off. It might be obvious when I have a look inside.

That was one thing I was going to try, but I wondered if it might need a decent voltage (although not quite up to Megger standard!) to see if there was any breakdown.

[Peter Parry]

Faulty mains filter capacitor allowing small leakage to earth?

[Brian Gaff (Sofa)]

I'd not imagine it would myself. Once this odd thing, was caused by a spider, literally in the connection block to part of the machine. That was a Whirlpool and there had been a tiny crack in the cover that had widened and the critter got in that way. Strange things occur with domestic appliances sometimes. sigh. Brian

[Brian Gaff (Sofa)]

Yes but that should not be affected by humidity or temperature. Back many years ago a certain model of Wima capacitors had this odd trait when the sealing plastic shrunk and left a tiny void around the wires. Brian

[tabbypurr]

Or it may be time for you to test it. Try the element first, it's suspect no 1.

NT

[John Rumm]

I spent some time chasing an earth leakage fault in someone's cooker once - in the end I had eliminated all of the internal components, and found the fault was moisture in the mains plug!

[T i m]

If not before the switch, I wonder it's only a single pole switch as if it was (I'm not sure if it's 'allowed' to be) it could still be a neutral to earth leak past it?

In our case is was carbon buildup on the (WM) motor brushes causing a N-E leak (and would trip the RCD with the power switched off at the socket but on on the WM).

I think our fault was quite measurable with my DMM and was seen to be cleared once I'd brushed / blown all the carbon out. The WM then carried on until the main bearing went again.

Cheers, T i m

[Adrian Caspersz]

The Guardian in daily mail mode...

[Jeff Layman]

I had a look inside, and the only part before the mains switch (double-pole, by the way) is the interference filter. It was a little sticky to touch, and might have leaked some of the potting, but it was difficult to tell. I removed it, and found it was marked: D.E.M. F£CF75005t

0.15uF (X1) + 1Mohm 2 x 0.027uF (Y2) 250V 50/60Hz 16A/40degC HMF 25/100/21C

There is a diagram too showing a 0.15uF + 1Mohm across the mains, and

0.027uF caps from live and neutral to earth.

With a multimeter it read 1Mohm across Live - Neutral. Live - earth and neutral - earth read open circuit (took a few seconds to get there at

20M range as the caps charged. Test voltage is only 0.3V). It was, of course, not possible to check the 0.15uF capacitor. On the capacitance range, Live - earth read 0.048uF, and neutral - earth 0.067uF.

It looked cheap enough to replace anyway, but:

No alternative listed, either.

Similar results at Partmaster (and other identical sites - do they all get them from Beko anyway?!), and others don't list it at all. It is available on eBay as a "genuine Beko part", but why there and not at other sites? I'll do a bit more checking on alternative interference filters, even if a small modification is required, as I'm not happy using an identical part which might be dodgy.

[Peter Parry]

These are not really type or manufacturer specific except for how some make the earth connect to the machine. Some do it via a flying lead and Lucar connector, others do it by a bolt through a small mounting plate. They are not an item which fails frequently.

[Andy Burns]

what about this

looks physically the same, same value/type of C and R

[Jeff Layman]

Thanks for the suggestions, but I really need one with 6 terminals for connection. I'll probably go with the one Andy suggested. I'd seen it while going through the options on the Beko site, but at that time was still looking for an original to replace that already fitted.

Maybe not, but evidently they can go with a bang according to some reviews I have seen!

[Jeff Layman]

I'll probably go with that design. I found this one on Amazon:

That looks Identical to mine, but a quick look at the reviews might explain why Beko no longer supply it!

[Peter Parry]

Y or X/Y class capacitors (used in the filter for line to earth filitering) are required to fail open circuit so there is no chance of them creating a live-earth path. X rated capacitors As they are in a sealed aluminium or plastic can the gasses produced by some failure modes can cause the case to rupture with interesting sound effects. X rated capacitors must not support combustion so there in no fire risk even if they make smoke.

[tabbypurr]

Your machine will work fine without it. Any brand is fine as a replacement. The values aren't critical.

NT