Tommygunn Posted November 10, 2015 Report Share Posted November 10, 2015 I've just replaced my staircase and bedroom G9 halogens with LED bulbs. However, I have noticed that the stairwell and two bedrooms have the LEDs ever so slightly lit even though all switches are off. There are two LED bulbs per room/area, on different walls, and each room/area has a 'two way' switch setup. One of these bedrooms did have a 'three way' switches but I removed one of those many moons ago. What is causing this? I presume there is some kind of wiring fault as this does not happen in the third bedroom (two way switch) or the bathroom (single switch), same bulb count and arrangement. Thanks, Tom. Link to post Share on other sites
xdave Posted November 10, 2015 Report Share Posted November 10, 2015 As LED bulbs require a lot less current to illuminate it is not uncommon to find this happens. Usually it is induced currents leaking between parallel conductors which were too small to exceed the resistance of the halogen lamps but provide enough current for the LEDs to illuminate. I don't know about Italy, but in the UK we tend to use twin solid conductors for live and neutral with a third solid conductor in between them connected to earth/ground. The earth conductor will provide a path for any stray current produced via induction and/or capacitance effects to be taken to ground. It was not uncommon in the past to have the lighting switch drops wired in just two core or two core and earth with the earth disconnected, resulting in the non-live conductor of the switch cable receiving a small current. Sometimes a one-way lighting circuit has been updated to be a two-way lighting circuit and the original earth conductor has been borrowed for a common strapper, removing the earth and causing the same result. Ideally you want to address the cause of the induction and/or capacitance effects (particularly if it is due to the lack of an earth conductor), but if you can't then installing a simple RC snubber circuit across the lamp fitting will do the job. They are simply a series-connected resistor and capacitor which have the effect of suppressing the interference. You can buy them ready-made for this purpose with insulated tails - Kemet part no. PMZ2081 for example. (Others are available for less, but you usually need to insulate the tails yourself.) Care must be taken not to inadvertantly remove the double insulated rating from any fitting, and an earth must be present because if the capacitor fails there is a risk of electric shock. They are installed across the fitting as close as you can get them. Link to post Share on other sites
hitmanNo2 Posted November 10, 2015 Report Share Posted November 10, 2015 I take it you have already ruled out gremlins? Link to post Share on other sites
Tommygunn Posted November 10, 2015 Author Report Share Posted November 10, 2015 Hitman, I'll see how things go before I get to that conclusion. xdave, I am actually English and UK solid core housing wire is my most hated wire type. Here in Italy they cement in that corrugated, plastic tube stuff through which they thread, in US terms, approx 14awg, for power, and 16awg, for lighting. All these wires are individual, flexible multicore and a much better system, if you ask me, for a number of reason, than our own method. All my lights have, obviously, a live and neutral but also an earth for the fitting itself, in the same way as the UK. I know that the house is fully earthed and all branches of the earth wire continually reduce to fewer and larger earth cables until they get to the main big, fatty earth cable at the main junction panel. I was browsing about and one thing showed up, which I sort of scan read. Is it possible, or does it make a difference, that the electrician might have puit the switches on the neutral as opposed to the live line? Just did a close inspection of the bathroom bulbs they too are on but very dim. The bedroom that I previously said were off might be on but they are too dim to say. There is definately an order of brightness when off; bottom of stairs is the brightest, top of stairs, bed 2 & 3, bathroom (slightly) and bed 3 (maybe?) Tom. Link to post Share on other sites
xdave Posted November 10, 2015 Report Share Posted November 10, 2015 Whilst it is often not a problem in terms of operation, on an AC circuit switching the neutral creates very dangerous scenarios. Remember that the neutral is connected to earth/ground at the supply point or nearby, and almost any conductive surface like a metal light fitting or switch will be connected to ground if it is not double insulated. Also remember that the neutral conductors are not normally interrupted in circuits unless the corresponding live side is also interrupted (if they are then the potential difference can rise to mains levels). With that in mind if the live side of the circuit is switched then the fitting will be at ground potential when the switch is disconnected, which is what people would expect to happen. If you come into contact with it during a simple everyday fault like replacing a blown lamp there is a very good chance that anything you touch (like the base of a lamp while unscrewing it) will be at roughly the same potential as you are, and safe. If the neutral side is switched then the fitting will always be at mains potential to ground. Unscrewing a blown lamp could expose you to death, or at best some very nasty life-changing burns. I would not recommend anyone test this, but if you were to touch an uniterrupted neutral conductor it would be unlikely to harm you fatally because the potential is very close to ground as you would be. If you did the same with a live conductor the potential difference would be pretty close to mains and as you are likely to be a very good low resistance path to ground you would pull as much current as your tissues would carry before either they melted or a protective fuse does. On the subject of protective fuses - I have seen a house wired in the 1960's where the live and netral were swapped in the distribution box/consumer unit. The rewirable fuses were all on the netral sides of the final circuits, so the only fuse protecting the installation (and anyone that came into contact with a fault) was the 100amp supply fuse (which will allow a lot more than 100amps through before blowing). The owner had complained of a tingling sensation from light switches after fitting new metal capacitive dimmer faceplates. Link to post Share on other sites
xdave Posted November 10, 2015 Report Share Posted November 10, 2015 I meant to add - if you want to test if it is capacitive coupling inducing a small current in the switched wire then you can just swap out one of the lamps in the circuit to one of the higher resistance halogens and see if the dim glow ceases. If it does an RC snubber will almost certainly stop the issue. If you believe that part of your installation might be wired with switched neutrals then please be very careful working on it and consider total isolation of the supply if in any doubt. If you have one, glowing screwdrivers are not safe indicators of live circuits. Use a device deisgned for proving dead circuits, or at least a multimeter to a known clean ground. Link to post Share on other sites
Tommygunn Posted November 10, 2015 Author Report Share Posted November 10, 2015 xdave, I'm sure everything is fine but I'll test the wires and see what is going where just to be sure. As you say, I always knock off the trip switches and probe with a multimeter. Tom. Link to post Share on other sites
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