Flashing bathroom light - whilst switched off!

[harryagain]

Pull the fuse/turn the mcb off and see what happens. Strong electric fields can cause a fluorescent tube to light up. HV cables nearby. Source of micrwave energy.

[GB]

Flashing bathroom light - whilst switched off!

This is 2 yrs after a complete rebuild. Recently, the bathroom light has started to flash whilst switched off. It flashes very briefly once or twice a second. It's a fluorescent 2D fitting, two wires, no earth.

I suspect one of three reasons: a) Problem with the switch that allows a small amount of current through. Seems unlikely. The switch looks fine, and the light switches on and off okay. b) Water ingress into the fitting. But this looks fine. No sign of water damage. And, in any case, it's switched off, so it should have no live feed. (Yes, I know that live and neutral sometimes get muddled up, but even so where's current going to without an earth?) c) Water ingress into the wiring somewhere where I can't see it. This is in a flat, so $deity knows what the person in the flat upstairs lets overflow.

Any help would be appreciated.

[Syd Rumpo]

Does it flash if removed from the socket but taped next to it? Do you have a radar rotating nearby? Is your neighbour a radio amateur?

Cheers

[ARW]

None of the 3 reasons sound likely:-)

Not many 2D light fittings do not require an earth - can you give a make and model no?

Is there an extractor fan in the bathroom?

[Graham.]

it's actually a common well understood phenomenon, caused by the capacitance in the order of a few hundred picofarads of the cable run to the switch.

What is needed is a high value resistor across the lamp to quench the voltage induced when the switch is off.

You may well find that changing the 2D lamp for a different brand will cure it.

[GB]

Sadly, I did not write it down. However, there were three wires coming into the lamp. Live and neutral were appropriately terminated, and the earth was just loose inside the fitting. I did not take it down and look what was behind it. I could not reach. I'll have to get a small steps to go in the car.

The girl in the upstairs flat keeps rabbits. I can't imagine that she has a radar set up there!

There is an extractor fan - in the basement. It's a centralised system, and I think it's timed, rather than humidistat. There were two wires to into each terminal of the light switch, so I assume one set connects to the extractor system.

[ARW]

It is not a problem I have never come across on 2D fittings (although that does not mean it does not exist). It is a well known problem for CFLs and LEDs with integral circuitry built into the lamp.

You should not use a resistor but a snubber (a resistor in series with a capacitor) to cure the CFL and LED flashing problem..

[tabbypurr]

+1, or a capacitor. Either way make sure its properly mains rated.

NT

[Davey]

It's a poltergeist. My mother-in-law had one, it would randomly turn her bedroom light on at night. It never harmed her.

[Brian-Gaff]

I'd still suspect something bridging the switch. It would not need much. Take the switch off then test it and see if it flashes.

I've seen this with these fangled electronic ballasts before. Really irritating. Brian

[Brian-Gaff]

If there is enough rf energy to do this then something is very wrong indeed I'd suggest!

Brian

[Brian-Gaff]

No sorry don't believe that. it is probably that there really is an earth. Did not say what sort of switch this was. We have ours outside the room and it has been known for there to be a slight leak from one conductor to the earth point on the metal box in the wall when the switch was screwed don. Enough to occasionally pop the breaker and to make the light appear to be on very dimly with occasional bright flashes. This was some years ago and some sleaving cured the problem, however I'm still suspicious of a switch leak.

Got a High impedance metar? Brian

[The Natural Philosopher]

Its normal on almost all installations. Wiring coupling allows small amounts of charge to be picked up by 'isolated' wiring and eventually there is enough charge in the reservoir capacitors to energise the unit

- for a tiny period.

Solution is a large value resistor across the live-neutral near the unit.

[GB]

No, I have a cheapo electronic meter in my toolbox, and an Avometer, which is nearly 50 years old. :)

The person whose light this is swears blind that her electricity bill has gone up dramatically since this started flashing. I don't believe her.

I'll change the switch and see if that helps at all.

[Davey]

One of those was up for auction recently. I remember them from my schooldays.

[Bob Eager]

I have three or four...!

[Davey]

Hang on to them, they might be worth real money.

[alan_m]

I guess as the generation of engineers that used AVOs die the price of those still in existence will fall through the floor. Their offspring will consign them to landfill during the house clearance. The only models that may be worth money will be those that survive for another 50 to 100 years, and then just because of their rarity value.

[harryagain]

Fluorescent tubes may light up if held in the vertical position under HV power lines. Video of it here. (Not much help to you I know).

[Huge]

I saw one in an antique shop, recently. A Mk8 for £40, IIRC.