Lighting problem


Postby Troller » Mon Oct 26, 2009 8:50 pm

I have a lighting problem.The landing light is operated by two way switches, one upstairs and one downstairs. The switches operate OK but when the light is switched off the bulbs glow very slightly. When checking the switched live feed to the light unit when light is meant to be off there is a small voltage 17 -18 volts present on the line! The light unit consists of 4 x 50 watt spot lights in a metal surround which is securely earthed (or I think it is). Can anyone offer any help as to what the problem might be?
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Postby sparx » Tue Oct 27, 2009 8:39 pm

Fascinating....
how is 2way achieved? ie at top switch how many wires, eg 1 in common, 2 each in L1 & L2?
If so note what goes where and what colours. if older wiring should have 3 core plus 2 core.
after making safe [supply off], disconnect 2 core wires (red/black) put in seperate connector blocks and switch supply on, does light still glow?
If so fault in light fitting, if not switch wiring suspect.
BTW is this a recent fault after changing anything? eg light fitting.
regards sparx,
Take care 230V kills!
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Postby Troller » Tue Oct 27, 2009 9:02 pm

Thank you for your response.

The top switch has 1 wire in the common and two each in L1 and L2 as you suggest. There is a three core and a two core cable. From memory the two core is red and black and the three core I think is red, blue and yellow. The problem is in my son's house (hence the uncertainty of the colours) and it will be a couple of days before I can try your suggestion. He has had the problem since he moved into the house about six months ago but said nothing until recently. The glow is very faint so it would be easy not to notice.

I will try your suggestion and let you know how I get on.

many thanks again.
Troller
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Postby ericmark » Thu Oct 29, 2009 2:07 am

I agree with sparx Fascinating.
The 17 – 18 volt I will guess you are measuring from line to earth and it is very likely you could get this in any healthy system as neutral and earth are only the same at the supply transformer in TT system or supply head in a TN-C-S system so not worried about that.
I have seen with CFU lamps the cables running next to other live cables has been enough to induce power into the cables, which act as a capacitor until a threshold is reached and then the lamp flashes.
However to get enough power to make a lamp glow would need more current than could be induced that way. So the next thought is when switched off the line being grounded and the 17 – 18 volt many be enough to give faint glow.
However I can’t see how with a two way system any connection could be made to ground which would not at some point cause a short and blow a fuse.
Next though is neutral and switched line swapped and you are not switching lamp off but switching it from series to parallel. Now this seems more likely but if this was case then likely other lights would be affected.
So expanding on that, what about a lamp seldom or never used? Now thinking on those lines, what about a loft, pantry, or other lamp?
So what I will guess is on the ceiling rose someone has at some time added another lamp but instead of connecting to the line and neutral they have connected to line and switch return. If the second bulb is smaller than the lamp in question (I’ll call it A) then A with switch on and off normally if B is off and on and glow when B is on. Lamp B will go on and off although not to full brightness when A is off and will not work when A is on.
Does that sound likely? Maybe you can get your son to check all cupboards, loft spaces etc. to see if he can find second lamp. Best looking when lamp A is switched off as then it is likely to be on.
As sparx says, you know there is a fault so any wire could become live so be very careful and please do tell us what you find.
The switch wiring sounds like standard two way wiring.
It is possible you have a borrowed neutral in some form some where, so even when the fuse is pulled or MCB switch off, you may get power, so knowing there is some odd fault, I recommend switching off at main incoming switch, which will be twin pole before doing any work. Just in case, it is getting power from some other circuit.
Do let us know what you find.
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Postby Troller » Thu Oct 29, 2009 4:33 pm

Thank you ericmark. What a reply. There are certainly enough suggestions (as well as those made by sparxs) for me to follow. I will be at my sons Friday afternoon so I will investigate and let you know what I find.

Troller
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Postby Troller » Thu Oct 29, 2009 7:45 pm

sparx, ericmark, I have just made a flying visit to my son's house to test out some of ericmarks ideas. There is a loft light that has been added by someone but don't know when.The loft light on or off doesn't have any effect on the glow of the landing light.

Three more bits of information:

1. The ceilng rose of the landing light looks as if it is the last in the wiring line, i.e. apart from the earth, neutral and live (switched) of the light itself there is only 2 wires in the earth, two in the live, 1 in the neutral and 1 in the switched live. From the relative positions of the landing, bedrooms and bathroom You wouldn't imagine the landing to be the last in the line!
Could there be a junction box somewhere?

2. On further questioning my son about when this glowing problem started he now tells me it was not when he moved into the house but shortly afterwards when he replaced the 4 bulbs with special (his words) bulbs that are supposed to last 30 years! He said he was given the bulbs by an electrician at work. Each bulb seems to be made up of several individual LEDs. I notice there are such bulbs available when I searched the net. Could this be the sole cause of the problem? Non of the other lights upstairs exhibit this 'glowing' problem.

3. There is an extractor fan in the bathroom and when the landing light is off but glowing and the fan is then switched off the 4 bulbs glow much brighter for about a second before returning to the normal glow. Nothing else upstairs affects the landing light glow and the fan doesn't affect anything other than the landing light.

One other problem which may impact resolution is that the loft flow is boarded over making access to upstairs lighting wiring difficult.

I will be back there Friday afternoon to continue investigations and will keep you updated.

Once again many thanks to both of you for your help.

Troller
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Postby Troller » Fri Oct 30, 2009 5:05 pm

Hi there. I have now investigated the fault further and done as you suggested. disconnecting red and black from the top switch stops the glow but I can find no fault with the two way switch wiring. I have checked the wiring to the light unit in question and all is in order.

I then took out one of the 4 LED type lights (GU10 12 watt 240v) and the glow persisted in the other 3, however when I replaced one of the four LED lights with a standard GU10 50watt bulb the glow immediately disapeared in all the lights! There are 2 more light units in the house that use GU10 50 w bulbs, one upstairs in a bedroom and 1 in the kitchen downstairs. When I replaced a standard bulb with an LED bulb in the bedroom light fitting there was no glow on any of the bulbs when the switch was off. However when I took out all the standard bulbs and just put in 1 LED bulb this glowed when the switch was off. I repeated this in kitchen dowstairs and got exactly the same results as in the bedroom. I have not previously mentioned that the upstairs and downstairs lighting circuits are fed by separate fuses.

I am not sure what all this means but it doesn't look correct to me. Surely it is not normal for these LEDs to glow like that.

Could there be something more sinister?

Any further suggestions would be very much appreciated.

Troller
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Postby sparx » Fri Oct 30, 2009 5:24 pm

Hi again, could well be the LED lamps; easy solution - change em!
well just to see if 'old fashioned' ones still glow! doubt it.
Many modern low energy lamps can give similar problems.
My Dad's new flat had perspex glowing switch locator plates which had a neon across switch contacts.
when he fitted low energy fluorescent lamps he found they glowed and flickered when off, just right for 'All Hallow's e'n'
Disconnected neons, problem solved, they were allowing just enough current through to cause glow but not enough on normal lamps.
happy hunting,
Sparx
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Postby advance diyer » Mon May 07, 2012 9:59 am

I have the same problem but in the kitchen, I replaced 6 x GU 50w down lights with 6 x GU 4.4w led cool white. Operated by a two way switch at either end of the kitchen. It did not matter what end they were switched off, they glowed, I re-wired, thinking the cct was at fault, placed them on a separate fuse way protected by a MCB via a RCD on the consumer unit, intercepted the 4 wire in the loft for the switch wire thinking induction could be the problem no change. (GLOW)
I have other LED in the bungalow no problem, the only difference is the kitchen is on a two way switch and the others are on a one way. L1 L2 COM are correct, I even resorted to taking the switch apart to measure the clearance of the contacts, different permutations on the L1 L2 COM.
I have changed the LEDs with a lower wattage but still the same glow problem.
One thing I have noticed depending which end is on / off you get a brighter glow.
Under cupboards are LEDs operated by the same double switch no problem.
My conclusion is either back to the old GU 50w or make it a one way cct. My wife will not be pleased.
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Postby ericmark » Tue May 08, 2012 8:39 pm

You could try bigger LED lamps. The problem is the wires act as a transformer and the induced voltage or may be even a capacitive coupling is enough to make lights glow. It normally does no harm likely if you use one tungsten lamp then rest as LED will work OK.
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Postby advance diyer » Thu May 10, 2012 6:54 pm

I Have almost sorted the problem. I have been back to the supplier of the LEDs and told the tec dept of the problem, they advise of a solution. Rather than go through all the jargon. I quote. THE OTHER WAY ROUND THE PROBLEM IS TO FIT A 62KOHM 1 WATT RESISTOR, MIGHT HAVE TO OPT FOR THE PREFERRED VALUE 68KOHM 1WATT IN THE UK. JUST CONNECT IT ACROSS ANY OF THE LIGHT FITTING FEED CIRCUIT.
I got mine from amarzon and will fit this weekend, Ill let you know if it works. (fingures crossed)
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