The hard and fast rules of coloured wires

But that changed to Brown for + and Blue for - in the uk a long time ago in some cases

Well white is the return (-) side of the LEDs in computers and I suspect other electronic units.

"> But that changed to Brown for + and Blue for - in the uk a long time ago in

No it has not!!!! The change to brown and blue was for MAINS AC wiring, which has no +ve and -ve.

Jeff

Hi Andy,

For DC there are no hard and fast rules. The usual convention is

• positive from ground = red

zero volts (ground) = black or white or green

- negative from ground = blue

But it's entirely up to you. Normally the "warmer" of the two colours will be positive with respect to the "cooler" of the two colours.

For mains AC, the legal convention is brown for line and blue for neutral (AC doesn't have plus and minus). Low voltage AC is usually both white or both black.

For electronic components such as LEDs, etc, the usual convention is that the longer lead is positive. You can remember that by mentally forming a plus and minus symbol out of the leads (+ symbol needs extra length for the cross arm).

regards,

Martin.

On 11/01/2007 15:15, Andy Sollis CVMRD said,

AFAIK there has never been any hard and fast convention. How positive is positive? At work, for instance, we tend to use black for 0V, but red, violet or yellow for various positive voltages. Blue is used for negative voltages, or white, or orange. Then another customer may have a totally different wiring convention - one uses your Henry Ford analogy, but as all wires are idented anyway the colour is actually irrelevant.

I've long since found that what I was taught at school doesn't reflect the real world :-)

Actually, there is a convention I've just thought of. When you're disarming a bomb, you *always* cut the blue wire :-)

I think it used to be red for live and black for neutral in some cables (solid core rather than flex) but I'm pretty sure that's changed to brown and blue now as well. Something to do with harmonising with other countries' colours.

peter

(After just getting my head around 3 phase supplies, the sparky on a site where I was working had to keep looking up the new cable colours as the generators used the new colouring system but the equipment being connected used the old colours!)

On 11/01/2007 21:43, naked_draughtsman said,

Ah, but this is all to make mains wiring much easier and less confusing!

The nice bright colours used for three-phase are now being replaced by dull colours that will be hard to distinguish in dirty, dark and dusty electrical boxes, black was neutral and is now one of the lives, and blue was one of the lives and is now neutral. Still, I guess the EU must know what they're doing, mustn't they? I'm sure there won't be any scope for dangerous errors and confusion, will there?

If you allow people to work in other parts of the EU, confusion will arise unless the colours are standard throughout. Inevitably some countries have to change their traditional colours.

Mark Thornton

I recently replaced a bathroom extractor fan and was introduced to the delights of twin-live four wire connections for the first time. The box which Screwfix sent me included an invitation to join "The Guild of Master Craftsmen" which gives you some idea of the entry standards required by that particular organisation. I've never replaced an extractor fan before in my life.

(kim)

I think the entry standerds are paying the fee

The message from "kim" contains these words:

Did you inform the Local Authority's building regs department that you were intending to do electrical work in the bathroom? When the new mains cable colours came in the regulations were changed: Kitchen, bathroom and outdoor electrical work is for qualified professional electricians only and they must supply a certificate to show the work is up to standard...

I thought it was a joke, but it's all too true. The amount of DIY electrical work officially permitted now is very limited.

I think there may also be something in the choices of colours to help the colourblind.

The IEE have always been the odd men out in the mondial electrical convention. It was showing up 30 years ago when German kitchen equipment and Danish Industrial kit were using Green as a line conductor. Europe decided that such conventions as Line & Neutral plus Earth were pointless and accident prone and so why not make the two line wires interchangable? Earth connections reserved for loads of >

David Jackson said the following on 11/01/2007 22:58:

You're right - it is true. The catch is that unless you're connected to the trade in some way, you won't know about it! The likes of B&Q will still happily sell you an extractor fan, but they will "forget" to tell you that you're no longer allowed to install it yourself. Apparently we're not even allowed to wire in a cooker any more!

Just to give you an idea of how daft the rule can be, at work we produce electrical and electronic widgets. Some of these are 3-phase control boxes. To test them, we plug them in, and poke about with live 3-phase around. We don't need special qualifications to do this. However, we need to move a 3-phase connection box which is part of the building wiring, but because we don't have the right bit of paper we are not allowed to do that and have to call in an electrician to do this job!

It's getting to the point where we won't be allowed to change light bulbs any more!

Not had much experience at defusing bombs but, when I were a lad in the early 50's, the company I worked for sold some Italian vacuum cleaners which had metal cases. The earth connection was red ! I think the live was beige. There was no standard mains plug at the time, the customer had to fit their own, very often a bayonet in the light socket. We managed to cull quite a large proportion of the local population with those things. We also had 3 mains voltages in our immediate vicinity. 110, 210 and

And then only for flex.

Fixed wiring (ie the stuff buried in the walls) has only recently changed to the new European harmonised colours.

MBQ

And even more confusion when the "foreign" sparky comes to the UK and finds there are now two standards, the old and the new, which, as has been pointed out wrt 3-phase, can be dangerously confusing.

MBQ

That is simply not true, anyone can still do the work. It is still perfectly legal to DIY in any situation.

Suitably qualified people can self-certify their own work and issue the paperwork.

If you DIY then you shouold inform your local councils building control officer who will arrange for an inspection. There will be a fee for a building notice but they are not allowed to charge extra for the actual inspection.

MBQ

There has been no change to what is permitted as DIY work. Only the inspection and certification regime has changed.

Yes you are if you first submit a building notice to the local authority. What you will not get away with is doing a shoddy job.

MBQ