RCD Trips when lights turned off !

[Andrew Mawson]

New installation. Four 'uplighters' each equipped with a G24-D2 bulb:

lighting circuit two way switched, sourced from the same breaker as other light circuits on that floor. Within two weeks the RCD for that bit of the installation has tripped five times when the lights are turned off. RCD was new, has been tested for trip point and time. Circuit (and whole installation) has been tested using up to date, in cal, certified 17th Ed equipment. Needless to say I cannot get it to trip on demand. Seems (but only an impression) to happen when lights have been on for a while).

Presumably there must be an imbalance on switch off sometimes causing this, but why not every time? Any one experienced anything like this, or has suggestions what may be happening? Back EMF surge from the ballasts or something? - I'm puzzled and so is my sparks.

AWEM

[Dave Liquorice]

New installation shouldn't be a borrowed neutral and I'd expect that to reliably trip not just "random" and after two weeks. The latter maybe due to other kit sharing the same MCB appearing and being a bit leaky though. So there is less headroom in the RCD for extra leakage.

Faulty uplighter? Connect only one and work through them one by one.

[Owain]

Temperature-related distortion of some component? Neutral-earth short? Borrowed neutral?

Owain

[Andrew Mawson]

I think borrowed neutral is almost certainly ruled out as it only happens maybe once in a hundred switching offs. (As Dave noted) Quite possibly a warming up of the chokes I suppose, but why only failing at the instant of turn off? Google did reveal a chap in Kent who had a very similar problem with some G24-D2 garden lights. He solved his problem by putting a snubber capacitor / resistor network (0.1uF in series with 47 ohms) across switched live and neutral so I may do that and see what occurs - but this shouldn't be necessary for an off the shelf B&Q light! I have another four of these lights in anther room with no issues!

AWEM

[ARW]

> Simple lighting circuit two way switched, sourced from the same

The first thing I do with a problem like that (assuming you have not got immediate access again to the test gear) is to stick on a 500W load to see what happens.

[Brian Gaff]

Sounds like back emf to me, though have to say, it is not a common thing to occur. I suppose if you judged it just as the max voltage was on the ballast, then the back surge would be greatest.

Brian

[Andrew Mawson]

>>> Simple lighting circuit two way switched, sourced from the same

As in "tune for minimum smoke" I suppose!

AWEM

[meow2222]

Simple lighting circuit two way switched, sourced from the same breaker as

When the switch is opened, it can arc momentarily. The resulting hf causes much increased current through the usual capacitance to earth.

Options: fit a snubber to the switch, or reduce the total load on the rcd.

NT