Strange problem with low energy light bulb

I have a light in the house which I have wanted to switch to a low energy bulb for a long time. The hold up was that I needed a very small bulb. At last, I have found a small enough bulb but something odd occurred as soon as I put it in.

When it is switched on, it works as expected.

When it is switched off, it blinks every few seconds. So, I guess that there must be a problem with the switch If it is passing nothing then it would seem impossible for the bulb to do anything. I did not notice any problem with the previous incandescent bulb but I guess that if the switch is leaking a tiny amount, the filament would glow too little to be seen.

I have a few questions:

What is going on? Is a tiny current leaking, building up a charge in a capacitor somewhere until a sufficient voltage builds up to spark in the bulb and discharge the capacitor, and then the cycle repeats.

Is it safe?

Will it wear out the bulb very fast?

Is it likely to be enough to replace the switch? (Actually three switches can turn this bulb on and off).

Might I have to replace the wiring? (Much harder than just replacing the switches)

-- Seán Ó Leathlóbhair

It may not be a switch problem but more seriously an animal , usually squirrel or mouse or rat has chewed the insulation along the wires going to the switch, now with charred insulation, so passing a bit of current - so get the wiring leakage/visually checked. Especially if you've had any unexplained fuses blowing or history of animal noises in loft or floor spaces.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Try the buld in another location. Give us moe information on the bulb.

Bruce

Thanks.

Normally, I would immediately try to isolate the cause by moving things around but, in this case, I dismissed the bulb as the problem since I thought that if the switch was passing nothing when off (as it should) then there was no way the bulb could do what it is doing. If the bulb is at fault then it is not the only fault (or so I assumed at any rate).

The brand of the bulb is Philips but I cannot tell you more until I get home and look at it. I will post again later with fuller details and the result of a test in another location.

-- Se=E1n =D3 Leathl=F3bhair

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Thanks for the advice.

We had some fuse problems many years ago but not on the lighting circuits. The problem was traced (by a proper electrician) to the ancient (bakelite) fuse box. It was replaced with a modern fuse box. The wiring was tested (but not completely inspected) at the time. Since then, we have not had any fuse problems. That was about 10 years ago.

I am not aware of any animal problems in the loft but, of course, that does not mean that there have not been any. Access to the loft is difficult since it is very small but not quite impossible. I will squeeze myself in and have a look.

-- Se=E1n =D3 Leathl=F3bhair

Hi...

Can't help wondering - it's not possible that one of those "switches" is a dimmer, is it?

Take care.

Ken

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A good question but no.

It is a landing light. There are three switches, one at each end and a third in the middle where a small corridor from the bathroom joins the landing. All simple on off switches (well they must be changeover switches but, from the user's point of view, they are just on off).

-- Se=E1n =D3 Leathl=F3bhair

Sounds like leakage to me, there may be a measurable voltage floating on the neutral. I has a similar problem with fluorescent emergency lights last year. If you are in the UK it might be an earthing fault.

Ron(UK)

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I am in the UK.

How does an earthing fault affect the lighting circuit? I thought it was just two wire. The earthing for the house in general was checked a couple of years ago when we changed the boiler. The gas engineer said that a change was required but I forget exactly what that was. The RCCB in the new fuse box is not tripping but does it apply to the lighting circuits?

-- Se=E1n =D3 Leathl=F3bhair

On a cold wet miserable winter day in the early 70's. I was troubleshooting a newish car, that wouldn't start, that had just been serviced by a car dealership. a few days before. To cut a long story short, they lubricated the Point Breaker mechanism with a clear Grease that they probably used for years with no problems ! With 2 to 6 Amps flowing, the contact mechanism probably cooked off any wet or conductive grease. With the newer Hybrid Transistor switched points the DAMP grease appeared as a Dead Short to the few milliamps required to actuate the Transistor.

I would suspect the switches (All three) are lubricated with a grease that is conductive enough read (dirty enough)to cause the problems indicated !

The quick and dirty, to clear the excess grease is to replace the lamp in question with a 60 - 100 watt bulb and switch On and Off a few times. in the Off position any conductive grease will be burned away.

Any fire Hazard, Not likely, after all these switches were manufactured and sold for years lubricated just like this, besides we are talking about a drop or two grease total ! If you are worried, replace the switches.

If this doesn't clear the problem than you may have exessive capacitative coupling between the various conductors due to the three-way switching, under a very light load !

Yukio YANO

In order to do that it must be getting power from somewhere. You must have a fault in the switch or related wiring.

Graham

That would appear to be the case.

Graham

How is this voltage induced ? Are you suggesting electromagnetic coupling ? That sounds astonishingly unlikely.

Graham

If the neutral wire isn't properly grounded enough voltage can be induced by or leak from other 'live' circuits, maybe enough to cause the fluorescent fittings to randomly flicker. It could be a faulty switch leaking across the contacts.

You don't live beneath an electricity pylon do you? It might also be the rays from guvmint mind control experiments entering your house. ;)

Ron(UK)

Your switches are wired wrong (they are switching the neutral (or cold) side of the line, not the hot side. As well, you seem to have a leakage problem in the circuit as well. This leakage could be a switch or some other device or part.

First step is to make 100% sure the switches are in the hot side of the circuit. That will likely solve your problem immediately. I'd guess there is a chance much of your house is not wired correctly from your description...

Not sure what building codes/wriing codes you have in the UK, but in the US this circuit would not have passed a building inspector.

Ron, when the switch is off, there is no circuit. The neutral potential literally doesn't matter.

Graham

Makes no difference. When the switch is off, the circuit is broken.

Graham

Could you fix your news reader so it correctly quotes and attributes the previous post?

Capacitive leakage from the HOT wire to the switch wire? That could trickle charge and cause an occasional flicker. Random spikes would leak through much easier, and cause random flicker. Try as cure a small capacitor (100NF)across the lamp terminals, just as long as the cap is much bigger than the parasite one.