General > General Technical Chat
Tumble Dryer woes
SteveyG:
It absolutely is a failure mode.
It's fine for it not to trip if there is DC bias exceeding the trip current on it's own, but the device will inherently be unable to trip under it's designed fault conditions whilst there is DC bias present.
The analogy would be a car with automatic emergency braking, but the system is not designed to detect pedestrians. However when a pedestrian is present, the brakes no longer work...
themadhippy:
--- Quote --- So 253V/15mA=16k9,
--- End quote ---
50v surely,as that's the maximum voltage permitted on the earth before automatic disconnection kicks in
Alti:
--- Quote from: themadhippy on October 02, 2021, 02:15:18 pm ---
--- Quote --- So 253V/15mA=16k9,
--- End quote ---
50v surely,as that's the maximum voltage permitted on the earth before automatic disconnection kicks in
--- End quote ---
The resistor value given is the smallest value that should work OK when connected in between L and PE, with any compliant AC type 30mA RCD, for indefinitely long. If the RCD trips with this value resistor in between L and PE, then there is a problem somewhere. Voltage out of range, wiring leakage, faulty tumble dryer, RCD too sensitive, etc.
ajb:
--- Quote from: themadhippy on October 02, 2021, 02:15:18 pm ---
--- Quote --- So 253V/15mA=16k9,
--- End quote ---
50v surely,as that's the maximum voltage permitted on the earth before automatic disconnection kicks in
--- End quote ---
If you can get 50V on the earth conductor with only 15mA then you have bigger problems than just a faulty RCD. That would imply an earth impedance of 3k3.
I'm not sure why the earth voltage matters here anyway, though, because what reference would a device have to measure the ground voltage against anyway?
Maybe this is a difference between wiring practices and devices in other countries from what I'm familiar with in the US. Here GFCIs don't care about the equipment ground at all, partly because they're the only legal way to fit grounding receptacles on ungrounded circuits (they have to be marked as 'GFCI protected' and 'No equipment ground' as well). Standard breakers don't have a neutral or ground connection at all, but GFCI and AFCI breakers do have neutral connections, since they can't work otherwise. The only device I can see going into a breaker panel that would have a ground connection at all would be some in-panel surge protectors that fit in breaker spaces.
I've seen photos/videos talking about consumer units from the UK but am pretty much wholly ignorant of how other places do their residential wiring. I'd be interested in learning about them.
Gyro:
--- Quote from: Wilksey on September 28, 2021, 07:34:20 pm ---...
Anyways, my condenser tumble dryer has started to trip the main RCD to the sockets, but not all the time, every now and then it'll just trip, most of the time it'll complete the cycle and it'll be fine, seems to be worse when there are heavy items such as towels in there, as it was tripping the entire house I decided to get a plug in RCD and plug the tumble into that instead, well, it trips the main RCD still.
So why would it not trip the inline RCD in the first place? The dryer seems to get very hot so I am thinking it might have some vents blocked or it could be a thermal switch, do they trip short cct?
Any ideas? I'd like to keep the machine as it works fine when it doesn't trip but if it is cactus then it'll have to get replaced, I don't really know much about dryers , but it seems to spin OK and the rest of the time it works and everything comes out dry, no puddles of water anywhere, as I say it is a condenser so the water is contained and emptied after each cycle.
Other than replacing it which I don't really want to do, if I can fix it and avoid landfill I will, I am a bit stuck for ideas.
Any suggestions much appreciated.
Cheers.
--- End quote ---
Focussing back on the actual appliance...
Firstly, is it one of the affected Whirlpool manufactured ones that are known to cause fires, which has slipped through the recall process? https://www.gov.uk/government/news/update-on-whirlpool-tumble-dryer-recall-progress. If so, discontinue usage immediately.
Secondly, is the element one of the enclose tubular types, as also used in electric ovens, washing machines etc.? The most common failure mode in these is increased leakage in the alumina powder insulation between the element wire and sheath when hot (which could tie in will long run time heavy loads). This is a common cause of RCD trips.
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