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Tumble Dryer woes

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Wilksey:
Thanks all, certainly got a few things to try / consider.

Alti:
Test your RCD for sensitivity. It must not trip with indefinitely long 15mA leakage and must trip with 30mA within specified time. So 253V/15mA=16k9, this should never trip. If it trips, you have problems with either RCD or the wiring, or both.

Putting second RCD in series is doable but that requires selectivity.

--- Quote ---the plug in one is quite old now, so I might get a new one and see if that helps, the fuse board isn't exactly new,
--- End quote ---
Also, your "condenser tumble dryer" sounds like sth modern. If you have AC type RCD then it is not designed and tested to trip in case the leak is something different than 50Hz AC.

If the leakage happens in between phase and protective earth, cleaning electrical wiring might help here. If the leakage is in between neutral and protective earth then this is unlikely you can clean that up.

SteveyG:

--- Quote from: Wilksey on September 28, 2021, 07:34:20 pm ---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?

--- End quote ---

Because the RCD in the consumer unit is seeing the cumulative leakage of the entire circuit plus every appliance on that RCD. It's normal to have some level of leakage and portable appliances can leak anywhere up to 4 mA under normal operating conditions without being considered faulty. Bear in mind things like condenser dryers and washing machines with inverter drives will have some kind of filter network on the AC supply which specifically diverts current to the CPC.

For example, the differential current between phase and neutral on my supply is about 19 mA steady state, but it varies considerably as appliances are used. It's likely just that the high integrity consumer unit just isn't suited to your particular usage anymore.

I would try to measure the earth leakage on the dryer in isolation if possible. If it tests OK then consider an RCBO based consumer unit.

SteveyG:

--- Quote from: Alti on September 30, 2021, 07:40:57 pm ---Also, your "condenser tumble dryer" sounds like sth modern. If you have AC type RCD then it is not designed and tested to trip in case the leak is something different than 50Hz AC.

--- End quote ---

The failure mode of type AC RCDs is NOT to trip in the event of saturation of the current transformer, which is why it is considered a safety issue and the correct RCD type should be used for certain loads. The false tripping should not happen no matter what the nature of the differential current.

Alti:

--- Quote from: SteveyG on October 01, 2021, 09:05:54 am ---The failure mode of type AC RCDs is NOT to trip in the event of saturation of the current transformer(..)
--- End quote ---
Yes, well AC type is designed and tested only for AC 50Hz-60Hz leaks. Whether it trips at DC, 1Hz or 1kHz is not specified. It is NOT a failure mode, it is the expected property of this device.

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