Weird behaviour of energy saving bulbs

[kmillar]

Hi all, I changed the light in the hallway, outside my bedroom, with an energy saver. Can't remember the exact make, but it's the folded tube type, as opposed to the 'bulb' shaped ones.

Anyway, the weird thing is, even when the light switch is OFF, the lamp gives a small dim flash every 10 seconds or so. I never noticed till I walked under it in the darkness last night.

I've removed the bulb and held it in my hand, and nothing, so it must be getting some 'energy' from the wiring, but how can this be even when it's switched off????

Any suggestions? All I can think of is that the wiring must be wrong, and the live is permanent and the neutral is being switched. Could this cause the flashes?

-Confused, Glasgow.

[Mike Harrison]

They will do this if fed a small leakage current. For example if switched by an electronic time switch, or a switch with a neon across it (sometimes used to help find them in the dark).

If neutral is switched, then capacitive leakage might also just do it.

[Nodge]

I'm sure someone else reported this effect in this newsgroup a couple of weeks ago. I believe the answer was that the live wire was inducing a small current in the neutral wire. I don't think it's anything to worry about. Someone who knows more may explain it better. Nodge

[Andy Wade]

electronic time

dark).

There's still capacitive leakage when the live is switched (the capacitance between the wires going to the switch and back). It seems to be enough to give this flashing effect with some lamps.

This is an FAQ. A compact fluorescent lamp has a bridge rectifier across the mains followed by a reservoir capacitor. These parts provide a DC supply to an electronic oscillator circuit (an inverter) that provides the high-frequency current for the lamp tube. What's happening is this: when the lamp is off there's no load presented to the oscillator and very little load on the rectifier. Any small leakage current in the wiring - quite normal, not necessarily a sign of a fault

- charges up the reservoir capacitor, via the rectifier. The voltage across the capacitor increases steadily until it's high enough to start the inverter and power the lamp, which lights. This lamp load now rapidly discharges the capacitor, the inverter stops and the light goes out. The brief flash is all over in a millisecond or so and the whole cycle starts again.

Try different makes of lamp. Some don't do it, probably because they've go internal bleed resistors. Also I guess it's much more likely to happen with the cold-start types (the sort that come on 'instantly'). The warm-start ones won't ever get through their pre-heat phase on leakage current alone.

[fred]

The cheap alternative (LT 20p) would be to add a bleed resistor across the lamp wires in the ceiling rose yourself, a 1Mohm one should do the job but you'll need one of the right voltage rating eg. Mapin's 0.6W range won't do but their 2W or 'high voltage' ranges will. Alternatively two 470k from just about any leaded range connected in series across the lamp will have sufficient voltage rating.

Easiest connection would prob be to twist with the flex side wiring before screwing down the terms and bare leads on the resistor(s) should be sleeved.

[Andy Wade]

That went through my mind too, but I think that introducing such non-standard things into the fixed wiring is not a good idea. It would need to be recorded on a note attached to the electrical installation certificate or last periodic inspection report (if any) otherwise it could confuse the hell out of anyone trying to do an insulation resistance test.

[fred]

Fair comment about the note but I'm not sure if I understand your point about the insulation test. The bleed would be directly across the load where a next-to-no-ohm incandescent would normally be. . . . . Just thinking about it again though, is a proper insulation test carried out with all loads disconnected (ie bulbs removed) and switches on/off as required, that would make sense for a comprehensive test, presumably with fixed loads such as water heaters and cookers being a special case?

[Lurch]

On Tue, 22 Feb 2005 11:03:15 GMT, fred strung together this:

But you can remove a bulb, as you should when testing, but the resistor would still be across the live cables.

Fixed loads should have an isolator so they can be turned off for testing.

[kmillar]

Thanks everyone for the excellent replies. I must admit, I rather jumped the gun at assuming a wiring fault, because since I moved into this house a month ago, I've found some real horrors going on behind sockets etc.

e.g Light switch in kitchen was tempramental, turned out that the wires behind the switch were not screwed down, just poked loosely into the holes. A socket I removed in the front room, had soo much insulation stripped (about 2 inches!) that there were live bare wires just folded up into the pattress. None of the earth conductors are sheathed, and none of the 'black' wires used as switched lives in the lighting circuit are sheathed. (I thought it was law that any conductors used as live should be appropraitely coloured, or sheathed?)

Anyway, thanks again everyone.

-K

[Tim Mitchell]

In article , kmillar writes

This seems to be quite common, I think the screws work or vibrate loose over time. I found two sockets in our kitchen like this.

OOerr, that doesn't sound nice

I have been inside a lot of light switches in various houses and have yet to see one with red sheathing on the switched live.

[Mike Harrison]

Can't see any point in red-sleeving at the switch end as it's usually obvious. Would be handy in the rose or junction box however.

[kmillar]

Yes I have never seen it in the 'real world' either, but was instructed it was necessary when I did some elimentary electrical training at college a few years back.

I was studying a degree in Electronic Engineering (B-Eng) and they actually PAID us to go to college during the summer break to study things like welding, domestic electrics, industrial electrics, tool making, plumbing and vehicle crash repairs. Apparently they wanted us to get a feel for the other industies which we would be working in. Was well worth sacrificsing summer break for!