Light circuit tripping when turning off

I had more or less the same problem and I suspected the ballast as well.

I replaced the suspect light fitting but also checked all the earth and other connections in the stove. (also high on the suspect list)

I don't know what solved the problem but it is OK now.

By the way I posted a picture of the patterns caused by the ballast on CR4 and was told that it is those 38 year olds are not used any more. (why the patterns?)

It's possible that you had a three-way switch that was reconnected wrong or replaced by a regular switch but had the same wiring - since it sounds like you had some upgrades - then when you turn it off it's shorting.

Check whether power factor correction capacitors are fitted in the suspect lights, possibly the new lights have them and the old ones don't.

Just,

I would like to sound an alarm bell here. I recently smelled wood smoke when leaving work in the evening. I checked around and found an old ballast that was quietly cooking off, and starting to burn the wall. Some of those old devices lacked adequate thermal protection and would start fires. If you are having any questionable behavior in the old fluorescents - beware and replace.

LG_DAVE

Thanks all for your input so far.

I can confirm that there are power factor correction caps in all the fittings (Checked this when we moved the building) but we did not "measure" them as at the time there was no reason to suspect anything like this.

I can also confirm that they are only getting warm (not hot) as per normal expected performance. At my work in the last few months we also had a flourescent balast cook itself. Evacuated 400 people and took an hour for the "all clear" to return.

At home, we have been plotting a scattergram of the lighting condition each time the circuit trips. (Which ones were on, which one was switched and so on.) Ironically, it seems more related to environmental conditions than anything else. Seems to happen after 5pm until around 1am when there is potential condensing atmosphere. Doesn't happen in the mornings when getting ready for work/school and so on (5am till 8.30am)

I'm now thinking of progressively replacing the light sets in some parts of the house and in the others there are now available LED replacement devices for flourescent tubes that I might give a try. (eliminates balast and capacitors from the circuits.)

Might even prototype some lamps at work. (We manufactur LED lamps amongst other things and there are the right resources there to do this properly.) Who knows, if they work well, we might start to manufacture them for general sale.

Any additional thoughts are still welcome.

Are the fluorescent fixtures grounded?

The light fittings are definately grounded as follows.

The supply circuit has active, neutral and earth and the earth is connected to the fitting. The building frame is also welded steel construction and the fittings are screw attached to that framing.

The meter box has the mandatory ground connection to a 12mm stake that is 2m into damp clay and the building frame has 28 x 18mm diameter steel (cyclone tie down fastening welded to the frame) bolts that each extend 1m into 2m deep concrete footings.

The water supply pipe for the house is also bare copper attached at more than 25 locations along the length of the steel building. That pipe extends more than 6m underground and would also provide some level of ground potential connection.

From the above observations I presume that the fittings are grounded and that the grounding is effective.

As an asside, the tie down straps paid for themselves in the first year after we moved in. There was a little storm that came through. Insurance estimates wind speed was around 200kph, it made a mess, but the house (generally) remained intact. (A couple of windows broke, furntiture moved around inside, floor coverings stripped and dumped in the hallway, lots of scared people) but that's another story.

If/when you replace those ballasts, check each of them for a sticker that says there are "no PCBs" contained. If there are no such stickers (old ballasts had PCBs), please dispose of them properly (not in ordinary trash). Don't know what the exact OZ rules are, but they are a health hazard.

Thanks for the reminder. I am fortunate in that where I work has contracted hazardous waste disposal contracts and our employer encourages "environmental responsibility" for the employees inclusing allowing us to put that sort of stuff into our hazardous goods waste (identified) for proper disposal.

I don't remember seeing any of those stickers on the ones that have been opened for inspection or fitment, so it seems that I'll eventually have 21 of them to dispose of.

Suspicions confirmed - happy to be of service, sah! Good on your employer, you may quote me on that.