RCD tripping

[pickles]

Whilst I'm sorting out my electrics in the bathroom I thought I would also run this one by you

My kitchen has a ring main all of it's own. Along with the usual sockets there is a waste disposer in the sink and a tumble dryer. If the tumble dryer has been used for any length of time running the waste disposer causes the RCD protecting the ring mains to trip. This problem will pass and everything will work normally after a few hours

Irritating

Strangely, if you unplug the waste disposer and run it through an extension lead from one of the other sockets also on the kitchen ring main it works fine.

The disposer and tumble dryer are close to each other and the obvious thought is some sort of warm damp air leakage from the dryer condensing somewhere in the ring, eg junction box and causing it to be a bit leaky so a bit more earth leakage from the disposer trips the RCD. Unfortunately there is absolutely nothing nearby this could happen to and looking at it after it's been used there is nothing even remotely damp that could be causing the problem.

Any bright ideas

 

[flameport]

A possible explanation:

1. Tumble dryer has some earth leakage, this is increased when hot (i.e. after being on for a while). Not enough on its own to trip the RCD.
2. Socket for the waste disposal unit also has some kind of fault - possibly corrosion due to previously being damp, or some other internal fault. Again, not enough on its own to trip the RCD.

Both together are sufficient to trip the RCD. Hence problem only occurs when dryer is hot, and waste disposal used from its own socket. Sockets elsewhere presumably not faulty so waste unit works fine from those. Or perhaps the other sockets are closer to the consumer unit, so the current in the cables is shared differently.

Suggested fix:
1. Clean out the tumble dryer (and not just the filter - open the thing up and clean it out properly).
2. Remove the socket for the waste disposal - any damp/corrosion/dirt etc. in there?
3. Also check the tumble dryer socket - could have been damaged by overheating.

For the small cost involved, probably worth replacing both sockets.

 

[pickles]

Thanks flameport but I have already done all of that. There is actually no sign of dirt damp or corrosion anywhere in the ring and it's sockets, it only went in in 1998 so it's not that old. The dryer is 12 years old (Miele) but sound and very clean, the socket is about 4 feet from this and also clean and dry. The waste disposer is only a year old (the old one did it too) and I have double checked it's sockets and connections, all clean and dry

I'm posting here because I have run out of ideas after much investigating the obviuos stuff about corrosion and earth leakage

 

[ban-all-sheds]

Strangely, if you unplug the waste disposer and run it through an extension lead from one of the other sockets also on the kitchen ring main it works fine.

Have you tried the extension lead into the usual socket instead of a different one?