Dodgy wiring to light fitting

[Distorted Vision]

I was trying to replace the light fitting in one of the bedrooms today to a MK Shockguard pendant fitting. When aI remove unscrewed the exisiting pendant fitting I discovered that there were three twin and earth cables. The black from two of the cables were connected to the Neutral of the light fitting. However, the black from other T&E was wired to the Live. The red wires from all three cables were wired to a connector block wrapped in electrical insulation tape.

Why has the black been used as Live? Is this cause for concern? Should I just go ahead and fit the new fitting or should I get an electrican to take a look at our wiring?

Many thanks!

[John Rumm]

This is standard practice for what is known as "loop in" wiring. Nothing to worry about.

The three cables are:

1) power in - probably from the previous light on the circuit (or the consumer unit if this is the first light)

2) power out: carries power to the next light - will not be there on the last light in the circuit.

3) Switch cable: carries the live to the switch, and the switched live from the switch.

Hence 1 and 2 need to be connected together to ensure power continuity. The neutral to the bulb can also be permanently connected.

The switch wire is unusual in that *both* its wires are live - one permanent, the other switched. When using red/black (or brown/blue) cable for this, the neutral coloured wire carrying the switched live should be marked with tape or sleeving to indicate it is really another live.

Piccy here (2nd one down)

[Bob Mannix]

No offence but as you have demonstrated you know nothing about conventional lighting circuits, I would probably advise the electrician! Everyone has to learn somwhere though - buy a DIY book that has electrical circuits in and find out why your installation is the expected one (aside from the lack of a red sleeve on the black - should be there but almost never is).

[Dave Plowman (News)]

Get a bit of paper and draw out the circuit diagram for a light fitting and switch, grouping the cables together as in TW&E. Include the feed into the fitting and the one on to the next fitting. It should all then become clear.

If you're not capable of drawing this out you need to do some very basic learning before attempting any electrical work of this nature, I'm afraid.

[Distorted Vision]

Thanks for the replies.

I really don't think I need to pay an electrician just to wire in pendant fittings when its something I can do easily myself. Yes I didn't know the neutral coloured wire was switched live but I really don't think I'd have much of a problem with electricial circuits. I have a 1st Class MEng degree in Electrical & Electronic Engineering....not that you learn anything useful like domestic wiring or lighting circuits of course.

[Pete Verdon]

Which one did you think was switched live then?

This is the only reason I'm making sarky comments when you apparently do have a problem with an electrical circuit :-)

Pete

[dennis]

It takes about ten minutes to find out about 99% of domestic wiring. It is simplified so that semi skilled people can do it. Getting it to work is easy. It takes effort and experience to be neat and quick.

[Dave Plowman (News)]

But you couldn't?

Patently you do. When faced with something like this that you don't understand the normal approach would be to draw out the circuit diagram.

And this didn't involve drawing and following circuit diagrams?

[Distorted Vision]

Yes could and I did this morning. I just wanted to ask why the black was live that's all.

Well I don't want to get into an argument over it but yes after drawing the circuit diagrams its clear how simple it is.

Well yes obviously, right up to advanced circuit analysis and theory.

[Bruce]

Please don't tell us that your day job involves anything that might impinge on public safety. ;-)

[Tim S]

Bruce coughed up some electrons that declared:

Gentlemen please...

The bloke could be a designer of ship engines, but never looked at a car ignition system in his life - which doesn't mean he couldn't fix it. It just means he lacks familiarity with components and practises common in a specified domain.

After all, black as phase is *just wrong*, but home electrics have made a common concession that buying a reel of red-red (or brown-brown) T+E is often not going to happen in the real world, so a common work around is tolerated. But it wouldn't necessarily be obvious to say, a panel designer, who might have umpteem colours available and always use the right one.

It of course might have been more obvious is the red sleeve was present, but they often aren't...

[Bruce]

That's the last time I'll risk my life on a ferry. ;-)

[John Rumm]

Yup, could I join Tim in suggesting some of the willy wavers pop the old boy away for a while.

[Distorted Vision]

LOL...almost but not quite and I'm setting myself up for even more stick by telling you what I do for a living! I originally went to Medical School and was studying to be a doctor but changed my mind switching to EE. Now I'm a Execution Algorithmic Trading Quant for an Investment Bank. No the sub-prime crisis, credit crunch and recession is nothing to do with me!!! Its very common for engineering graduates to end up in The City when they realise that good engineering positions for graduates are hard to come by and generally compared peanuts compared to the Square Mile.

So I've not looked at circuit diagrams for a few years but the po> Bruce coughed up some electrons that declared:

[Bruce]

There are times I wonder why I ever stayed in Engineering. ;-)

Lighting is something I rarely touch because there always seem to be too many wires of the same colour. :-(

[Dave Plowman (News)]

Same applies to any complex installation. Use cable markers if needed. Standard wireman solution.

[dennis]

I bet some of my lighting circuits will confuse some electricians.. I used triple and earth for the drops as I ran short of twin and earth. They will wonder why it has a neutral and two lives.

[Dave Plowman (News)]

Triple and earth has never used the contemporary colour for neutral. Only for line. So 'they' should not assume anything.

[Bruce]

I know, but I am easily confused, so leave all but the simplest lighting wiring to others. I'm OK with ring mains. ;-)

[Alang]

That's what masking tape and marker pens are for