New wall lights don't work

Postby tdrath » Sat Apr 26, 2008 1:47 pm

I am trying to install a pair of replacement light fittings, but cannot get them to work. I removed the old ones and threw them away, but when I came to fit the new ones, they just don't work.

I'm pretty sure that I've wired them in an identical way to the old lights. The only obvious difference is that the new lamps incorporate a switch.

I took the new fittings off the wall and tested them by connecting them to the mains - they worked fine.

Any hints, anyone?
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Simply Build It

Postby ericmark » Sun Apr 27, 2008 1:38 pm

Unlike ceiling mounted lights, there is no convention for fitting wall-mounted lights. These are often feed from ring main, through fused spur units. And as electricians we can often spend quite a bit of time working out how they are wired. But a few pointers.
First there are two connections to every circuit Line and Neutral they are both considered as Live wires as in certain conditions they can both give a nasty belt. We also refer to switch as being the wire controlled by a light switch. I don’t know age of your house I will assume before wiring changed from red and black to brown and blue if not you will need to read new colours for old ones.
1) Often switch wires are black in theory they should have a red sleeve but often this falls off or was never fitted.
2) Lamp feeds are often daisy chained and the fault can be a previous lamp rather than one your working on.
3) Wire finders are very handy for checking without physical contact with the cable but only find the line wire not neutral so a neutral fault is hard to find.
As electricians were are weary of talking about using a meter or neon screw drivers volt sticks and the light as it is so easy to buy inferior products which are not safe. The leads on many meters sold in B&Q etc do not conform with BS38 and are not intended for mains work. Any meter with an Amps range except for clip on types can by selecting the wrong range cause nasty burns due to ionisation of the air and unless you have some formal training I would recommend you recognise your limitations and call in an electrician injured pride is far less painful than electric shocks. We will help and will answer any further questions, but only you can recognise your limitations.

Postby chris_on_tour2002 » Mon Apr 28, 2008 3:54 pm

following ericmark's comments with regard to cheap multimeters i have taken a closer look at mine. its a digital clamp meter, kewtech kt200. tests amps, volts and ohms. bought from a reputable electrical wholesaler for £45. not a dirt cheap one but no megger either. i have checked the gumpf that came with it, nowhere does it say that it is bs38 conforming but it does say that the safety design conforms to iec61010.

present condition of my particular meter aside (assume that its good and recently calibrated) as its only really for occasional use (thats all it gets) is it ok? is this a reputable brand? or should i upgrade?

i've always worked on the principle that i buy the best that i can afford.
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Postby ericmark » Mon Apr 28, 2008 6:10 pm

GS38 not BS38 stands for General Series and it says:-
The test probes and leads used in conjunction with a voltmeter electrician test lamps or voltage indicator should incorporate the features listed below.
(a) The probes should:
(i) have finger barriers or be shaped so as to guard against inadvertent hand contact with the live conductors under test: and
(ii) be insulated so as to leave an exposed metal tip not exceeding 2 mm measured across any surface of the tip. Where practicable it is strongly recommended that this be reduced to 1 mm or less. or that spring loaded retractable screened be used etc etc.
In the Introduction it says:-
2. The Electricity at Work Regulations 1989 (EAW Regulations) make it quite clear that no-one, however well qualified should be put at risk from electricity. If live working is really necessary. suitable precautions must be taken to prevent injury. It is often necessary to test for the presence of voltage or to measure voltage on power circuits. motors, switchboards, cable terminations etc. Electricians need to avoid the dangers of electric shock and burns by their training, technical knowledge and skill, ie their competence to work safely. combined with their use of safe test equipment.
It is referred to again and again when studying for your C&G 2391 but I will admit it took some pushing to get a copy had I realized it was only £2 I would have gone to local book shop.
If you look in RS components for replacement leads it states which comply as working on electronics they are far too heavy and not really required. It is rules like why when working for GEC LST I was not allowed to use any of my own tools or meters as under their Health and Safety policy they realized unless they provided the tools they had no control I got in a lot of trouble for using my own crimp pliers which would do all three sizes instead of theirs which only did one size each as mine were not calibrated. Yes even calibrated crimp pliers.
Domestic Electricians don't ever see this side of industrial electrics it is a different world.

Postby chris_on_tour2002 » Mon Apr 28, 2008 6:23 pm

how on earth do you go about calibrating a pair of pliers??!? there's health and safety and diminished common sense. and jobs for the boys of course.
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Joined: Thu Aug 30, 2007 9:14 pm

Postby ericmark » Tue Apr 29, 2008 1:02 am

We are talking about the type that have to crimp to set point to release not cheap DIY types and the jaws print a letter or number in the plastic to identify which set were used and it is this attention to detail that allows power stations to run programmed shut down to programmed shut down with minimum of maintainance. One wire coming lose could cause whole power station to have to come off line and with 7 days run down time just think what one lose terminal will cost! As I said different world to domestic.

Postby chris_on_tour2002 » Tue Apr 29, 2008 9:48 am

just removed the ceiling rose in my bathroom to replace the light and have noticed that there are 4 reds and 4 blacks (5 including the pendant). on the red side, two are obvoiusly the loop, one goes off to the switch. so what's the other one?

could it be feeding another light or some kind of spur?

i was hoping to run a spur from one of the loop wires for the shower processor but may have to run if from elsewhere if its already spurred.
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Postby chris_on_tour2002 » Tue Apr 29, 2008 4:33 pm

just removed the ceiling rose in my bathroom to replace the light and have noticed that there are 4 reds and 4 blacks (5 including the pendant). on the red side, two are obvoiusly the loop, one goes off to the switch.

i have managed to access all the wires in the attic and have discovered that the mystery additional wire is in fact a spur feeding the light in the toilet. i confirmed this by looking at the rose in the toilet and as expected there are two red and two blacks.

two questions:

i) is this a safe way of doing things? i assume it's fine. of course it would be better for me to incorporate the toilet light back into the loop and take out the spur but am i worrying unnecessarily? whilst the wires are just about accessible space is tight and i'd rather not do any work if it's not strictly necessary.

ii)i was hoping to run a spur from one of the loop wires going into the light for the 3A processor unit for the shower, by teeing into the loop leading up to the offending bathroom light. as that light is already running a spur is this ok? i can't see why not.

any advice?
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Postby ericmark » Tue Apr 29, 2008 8:18 pm

(i) Quite normal
(ii) I would look at coming from toilet. Anything for easy life.
Jobs like this where your not quite following the norm are very much decided on a on site gut feeling and really not the sort of thing you can do remote. Too easy to miss somthing.

Postby tdrath » Mon May 12, 2008 11:23 am

Back to my wall lights...

Well, I had an electrician in who spent an hour trying to work it out and concluded that the wall lights were on a 12v circuit. I thought this was an interesting conclusion, since we've been using normal lamps (with 240v bulbs) for the last ten years, so bought myself a multimeter and measured the voltage. I get 125v, or 160v at the switch.

I've worked out that the cable to the wall lights goes via one of the two ceiling roses, which I fitted just before trying to do the wall lights. Would a poor connection on the terminal block in the rose lead to a loss of voltage? Or a break in one of the conductors?
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Postby ericmark » Mon May 12, 2008 1:23 pm

Sorry your post did get hijacked.
1) Voltage is measured between two points and switches don’t have two points as there is normally no neutral sometimes we measure to earth which on a high impedance meter is normally good enough, but if you measured between line in and line out then size of bulbs and impedance of the meter will affect the reading and no guarantee that earths are connected which explains readings not around the 230 volt mark. Quite obvious mains voltage, although even with a 12 volt system the switch would still be at mains voltage as the transformer would come after the switch. In all the reading tell us very little.
2) If it was 230volt then very likely it still is. I don’t like neon screwdrivers but sometimes they are handy if neon lights it’s not 12 volt. Also neon will light even if the neutral is missing which brings me on to 3.
3) It is very easy to lose neutrals with ceiling roses. Both the neutral and switch return are both the same colour (black or blue) the switch return should have a sleeve (red or brown) but it often falls off. Most lights are wired as a radial so then can be affected by light before.
4) If the meter has high ohms per volt connecting it to a dead wire that runs next to a live wire can give a reading in the same way in which florescent tubes will light up under pylons be warily of odd reading like the 125 and 160 volt it could be induced from cables near to it.
You seemed to think you had wired correctly in first place I would tend to assume you had and that the fault is more likely to be in ceiling rose. I would also expect a neutral rather than line fault.
I am sorry the electrician did not sort it. Not all electricians are as good as they should be. Especially at fault finding. I would look for another, those working in industry on maintenance are normally good, they would soon get the sack if they weren’t but installation electricians are more concerned with what it looks like and if it complies with regulations how high the sockets are etc. There is a big difference between maintenance and installation although some electricians can do both.
Do take care. You have already read posts on meter leads.

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