My utilities room has its own ring circuit protected by a 32A RCBO.
The only loads on this ring are a Miele washing machine and a Miele
tumble drier, which have been operating just fine for about two years.

This morning, I ran the washing machine no problem. When the wash had
finished, I transferred the small pile of clothes to the tumble dryer.
I set the tumble dryer going and after about 20s, the RCBO tripped.

I wanted to test whether the RCBO was faulty, so I ran an extension
cable from another ring circuit (also protected by a 32A RCBO) and
plugged the dryer into the extension cable. 20-30 seconds after
switching on, the RCBO tripped.

I'm assuming that since the RCBO trips after almost half a minute, the
fault is overcurrent rather than earth leakage.

The filter in the tumble dryer is clear. Any other things I could
check to find out what is causing the overcurrent in the tumble dryer?

In article ,
Pandora writes:
My utilities room has its own ring circuit protected by a 32A RCBO.
The only loads on this ring are a Miele washing machine and a Miele
tumble drier, which have been operating just fine for about two years.

This morning, I ran the washing machine no problem. When the wash had
finished, I transferred the small pile of clothes to the tumble dryer.
I set the tumble dryer going and after about 20s, the RCBO tripped.

I wanted to test whether the RCBO was faulty, so I ran an extension
cable from another ring circuit (also protected by a 32A RCBO) and
plugged the dryer into the extension cable. 20-30 seconds after
switching on, the RCBO tripped.

I'm assuming that since the RCBO trips after almost half a minute, the
fault is overcurrent rather than earth leakage.

That's not a valid assumption.
I would suspect it's actually earth leakage.
It might be from the heater, only happening when it's
got to a particular temperature (sagging element, possibly
contacting dust or local overheating due to dust?).
Another possiblilty might be condensation running
somewhere it shouldn't.

The filter in the tumble dryer is clear. Any other things I could
check to find out what is causing the overcurrent in the tumble dryer?

I might try running it with the heater disconnected.
Depends how safely you think you can do that.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 6 Jan, 12:49, (Andrew Gabriel) wrote:

I might try running it with the heater disconnected.
Depends how safely you think you can do that.


Thansk, Andrew.

The tumble dryer has a "cool air" setting.

I've tried running it on this with a light load - and after 15 minutes
it hasn't tripped the RCBO.

Does this mean that I need a new heating element?

In article ,
Pandora writes:
On 6 Jan, 12:49, (Andrew Gabriel) wrote:

I might try running it with the heater disconnected.
Depends how safely you think you can do that.

Thansk, Andrew.

The tumble dryer has a "cool air" setting.

I've tried running it on this with a light load - and after 15 minutes
it hasn't tripped the RCBO.

Does this mean that I need a new heating element?

Possibly, but it might be fixable with just some
simple maintenance, such as blowing the dust out.
Can't tell without inspecting the element.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Pandora wrote:
My utilities room has its own ring circuit protected by a 32A RCBO.
The only loads on this ring are a Miele washing machine and a Miele
tumble drier, which have been operating just fine for about two years.

This morning, I ran the washing machine no problem. When the wash had
finished, I transferred the small pile of clothes to the tumble dryer.
I set the tumble dryer going and after about 20s, the RCBO tripped.

I wanted to test whether the RCBO was faulty, so I ran an extension
cable from another ring circuit (also protected by a 32A RCBO) and
plugged the dryer into the extension cable. 20-30 seconds after
switching on, the RCBO tripped.

I'm assuming that since the RCBO trips after almost half a minute, the
fault is overcurrent rather than earth leakage.

To trip a 32A type B MCB by over current in 20 seconds would take a
sustained load of some 130A+ - that ought to take out the 13A fuse in
the plug long before. The alternative might be if the heater is
switching in after that delay, and it has gone dead short - that may
take out the RCBO by fault current, but even then it would be unlikely
the fuse would survive repeated attempts. Hence earth leakage is a more
probable cause I would guess.

Have you got a non RCD protected circuit you could run it from? If so,
just letting it get hot enough for one drying cycle may fix the problem
if it is leakage caused by water being some place it should not be.

--
Cheers,

John.

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Pandora wrote:
snip

I'm assuming that since the RCBO trips after almost half a minute, the
fault is overcurrent rather than earth leakage.


More likely that the heater element is not switched on until the
tumbling has settled down and the heater trips the RCBO as soon as it
comes on...

Just an update to close this thread:

After leaving the tumble dryer for a few days to "air", the dryer is
now working again.

The dryer is a condensing type with a removable container for the
water. Wonder if I spilled a bit into the back of the dryer when
removing the container? That might account for the leakage current
last weekend.

Anyway, thanks to all for comments.