Nuisance Tripping Of Garage RCD

3 Feb 2008
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United Kingdom
Garage is wired with approx 30 meters of 4/2.5mm cable & supplied via a 32amp MCB from the house distribution unit - no RCD is fitted into the house dist unit.

Switching off fluorecent light in garage trips the RCD fitted inside the separate garage distribution unit.

Renewing the complete light fitting and rewiring lighting circuit has made little difference - it still trips the garge RCD approx every 10 light switchoff's

Now I'm getting fed-up because the RCD also feeds the socket which is the supply to freezer so I get some hazzle from the wife!!

In desperation, I split-off the lighting cct feed within the garage dist unit to 'by-pass' the RCD. The problem is far less frequent but still occasionally happens???

Could it be some back emf off the fluo chokes??

Think I will replace RCD in garage consumer unit with normal circuit breaker and then fit an RCBO instead of the 32a MCB on the house distribution unit.

Any thoughts out there??
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Sounds like a high resistance N>E fault somewhere.

The spike from switching the choke is just pushing the fault over the 30mA limit of the RCD.

I agree - think it's time to dust off the old megga.

Hope it not the supply line to the garage which is under the block paved drive!!

Thanks for response.
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No have not ramp tested RCD - don't have the kit. Will have to test by substitution.

Thanks for advice
Sometimes the RCD is faulty and trips before it should. Anything much less than 18mA (for a 30mA RCD) should be regarded as suspect.

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