Clothes dryer heating element earth leakage issue!

[AmmoJammo]

We have a clothes dryer, that the element leaks to earth... but only as it heats up.

Its a tube style element, with the actual element wound inside, I assume surrounded by ceramic powder?

Cold, I measured 10 meg from live to earth, but as the element heated up, it tripped the rcd, at which point, it measured 15k...

Why is it so!

Thanks!

[Richard Head]

Forget about a multimeter for isolation tests. The test voltage is way too low.
Use a megger set to 500V and you'll almost certainly see a much lower leakage resistance.

[AmmoJammo]

Forget about a multimeter for isolation tests. The test voltage is way too low.
Use a megger set to 500V and you'll almost certainly see a much lower leakage resistance.

Why is there leakage?

Why is it greater when its hot?

[Richard Head]

Without opening it up I would have to speculate why it's leaking the earth.
Possibly due to moisture absorbtion. (most likely)
Possibly mechanical contact due to poor manufacturing.
Possibly a lightning induced transient caused an internal arc (which partially healed itself).

[AmmoJammo]

Would the element be hygroscopic?

This is (I believe) a brand new element, that's been in storage for years and has only just been put in to service.

[Delta]

Buy a new element.

[ozwolf]

So, here's a story for you, but try it out at your own risk.

It is likely to have some moisture inside.  Many years ago, my father in law lent me a hotplate with a single element.  This hotplate had been in the cupboard for a few years.  I plugged it in and it immediately tripped the RCD.

I went to a repair shop to buy a new element and the guy behind the counter said to hook up to a non-RCD protected power source, and run it red hot for about 10 minutes to drive out any moisture.

It's worked perfectly on any RCD protected circuit since then.

Ozwolf

[RGB255_0_0]

Happens every time I clean the hob. One of the plates will trip the RCD so I stick a hair dryer on it for 5 minutes, let it rest and another 5 minutes and it's OK.

[HackedFridgeMagnet]

Happens every time I clean the hob. One of the plates will trip the RCD so I stick a hair dryer on it for 5 minutes, let it rest and another 5 minutes and it's OK.

Why are they called Hobs?

[Delta]

Happens every time I clean the hob. One of the plates will trip the RCD so I stick a hair dryer on it for 5 minutes, let it rest and another 5 minutes and it's OK.

Why are they called Hobs?

I've never thought about that!  Goooooogle tells us:

    1.
    British
    a cooking appliance, or the flat top part of a cooker, with hotplates or burners.
        a flat metal shelf at the side of a fireplace, having its surface level with the top of the grate and used especially for heating pans.
    2.
    a machine tool used for cutting gears or screw threads.
    3.
    a peg or pin used as a mark in throwing games.

Origin
late 16th century (in sense 3): alteration of hub. Sense 1, ‘metal shelf by a fireplace’, dates from the late 17th century.

Which does make sense.  What do you all it down under?

[AmmoJammo]

So, here's a story for you, but try it out at your own risk.

It is likely to have some moisture inside.  Many years ago, my father in law lent me a hotplate with a single element.  This hotplate had been in the cupboard for a few years.  I plugged it in and it immediately tripped the RCD.

I went to a repair shop to buy a new element and the guy behind the counter said to hook up to a non-RCD protected power source, and run it red hot for about 10 minutes to drive out any moisture.

It's worked perfectly on any RCD protected circuit since then.

Ozwolf

I was going to run it off four 24volt transformers in series, so its isolated, and at a lower power, for a few hours, to hopefully dry the moisture out

But! I wasn't sure if this was even a thing, or if something else could have gone strangely wrong..

[Richard Head]

Just place it in the oven for a few hours at 100 Deg C. That should drive off all moisture. No need for transformers etc.

[HackedFridgeMagnet]

I call it hotplates or stove.
But I've seen switches marked "Hob" and knowing they were for the hotplates I initially thought it was a spelling mistake.

[AmmoJammo]

Just place it in the oven for a few hours at 100 Deg C. That should drive off all moisture. No need for transformers etc.

The elements are all the way at work, and I'm too lazy to remove them from the dryer and bring them home! (long story...) 

[RGB255_0_0]

Happens every time I clean the hob. One of the plates will trip the RCD so I stick a hair dryer on it for 5 minutes, let it rest and another 5 minutes and it's OK.

Why are they called Hobs?

No idea. I guess it's a colloquial term. Not in the same way as "hoover" is used. I just had to Google cooker hob and got 3.8m results. The hob and cooker are often run on separate circuits here so using cooker and hob can remove some ambiguity on the consumer unit.

[Delta]

The hob and cooker are often run on separate circuits here so using cooker and hob can remove some ambiguity on the consumer unit.

Hob = hob
Oven = oven
Cooker = Hob and oven in one unit.


{/PedanticSparkyMode]

[RGB255_0_0]

The hob and cooker are often run on separate circuits here so using cooker and hob can remove some ambiguity on the consumer unit.

Hob = hob
Oven = oven
Cooker = Hob and oven in one unit.


{/PedanticSparkyMode]

/grill 

[madires]

Just place it in the oven for a few hours at 100 Deg C. That should drive off all moisture. No need for transformers etc.

30 minutes at 200°C worked for me several times.