Extractor tripping RCD after turning off...

[Mowgli]

Wonder if anyone can help here. I have a new extractor, a1.5kW Jet thing. Secondhand but good nick. It's plugged into a 13A socket (motor name plate says 4.8A) and runs just fine starting up and for long periods. However, it trips the RCD a few seconds after switching off as it's spinning down. The socket is controlled by two switches which are wired '2 ways', so either will switch it on or off, just like how light switches are wired up.

I thought the problem could be the motor generating current into the neutral while spinning down, or perhaps something to do with a build up of static. The old extractor was fine with this arrangement, although only 750W.

The earth is always connected, and only the live is switched. Do I need a double pole switch so both live and neutral are switched, if the problem is do to with the neutral being connected whilst spinning down?

Cheers!

 

[Spectric]

An RCD works on a difference between live and neutral due to some leakage of more than 30 mA to ground, if you used a double pole switch then it would isolate both the live and neutral so no inbalance.

 

[Sideways]

Try it in a different socket protected by a different rcd.
RCDs have a finite life and do fail.
An induction motor shouldn't trip an RCD. Phase shift, power factor, inrush all affect the live and neutral currents together so there isn't an imbalance to trip the RCD.
I've had a couple (of motors) that did, but the windings in both of those had been overheated so that the varnish was blackened and didn't insulate properly anymore, hence leakage to earth. They would run if plugged into a normal circuit breaker but tripped an RCD instantly, not after switching off.
Same would apply if there was earth leakage within a run capacitor that happened to have a grounded metal can

 

[Mowgli]

Turns out the extractor works fine when using the built in start/stop button, so it's definitely something to do with the neutral remaining connected after switching off on the current arrangement. Will try a double pole switch

 

[trvlr]

Double pole (DP) switches and sockets are my preferred for any machine etc.. Even my kitchen sockets are DP rather than SP; as are all the sockets in my garage/shed. They don't cost that much more than SP.