SL, N and L any good UK Electrical theory book?

Hi, this is my first post and I admit, I have not read the rules yet, so please go easy on me.

I am not a qualified electrician but come from a science background so I know the basics quite well. Recently, I replaced an old PIR Bulk Head with a new PIR Bulk Head. While replacing the light, I found out that the old one had 3 terminals SL, N, and L where as the new one has only got N, Earth and L.

Moving on, I noticed that yellow wire being used for SL in the old light. Traced it back to the wall switch and figured there were 3 Red wires connected to the L in the wall switch and Yellow wire (it had a red sleeve over it) connected to L1. After carefully examining and using a line tester, I figured I cant hook up Yellow wire to the earth terminal on the new light as turning the switch on will supply the current to the internal metal cover.

To me it seems like the stupidest thing ever to use Yellow wires for switching. The house was built between 1999-2001 and have the original wiring. Anyhow, I figured out the correct connections through the wall switch and placed the 2 Red Wires to L and the one (Red) going to the light to L1. Now, the light works well with PIR functioning as expected with ability to override it etc.

I then checked hallway and landing area switches (the ones with double switching) and they are also using Yellow wires for switching. Checked a few other wall switches without double switch and they have the usual Black/Blue and Red/Brown combination.

a.) Is this standard practice to use Yellow wires for double switches?

b.) What is SL? It's easy to understand N (Neutral), L (Live, Line or Hot Line) and Earth being Earth. Does SL stands for Secondary Live?

c.) Are there any good electrical books which covers the fundamentals, historical standards and current regulations?

Thanks

 

SL = Switched Live

Any colour can be used for any purpose, the one exception is that bicolour Green/Yellow should be used only for Earth.

Part of the skill of an electrician is to be able to work out how the circuit has been configured and then which colours are being used for which purpose. That skill comes mostly from experience.

 

DS

 

The yellow wire (correctly sleeved with red) is - or was until you disconnected it - being used as the over-ride for the PIR.

So you could (have) used the switch as a way for the light to be on permanently when you operate the switch.

All of the wiring you describe is (was) perfectly normal. What is defective is your understanding of it!

 

@bernardgreen: Surely, Colours don't matter and electricity wouldn't care either, as long as it has the conductive material and circuit completed correctly. My point is: Electricity is not art but science. Why anyone would not follow the industry standards and start using arbitrary colours?

@Taylortwocities: you are missing an important detail: the old light had SL,N, L and no Earth where as the new one does'nt have SL at all, it has L,N and Earth. The new light has different internal circuit. Essentially, at the light end, I had a un-switched Live (RED), a Switched Live Yellow (mind you the red sleeve on yellow was only at wall switch end) and then a Neutral. If I had just gone by the colours then there would have been no switched Live to the light. I could have supplied Siwtched Live to the internal metal plate. Although it would not be a disaster but not ideal. The Switch simply wont function and I would have no way of overriding PIR.

 

There are no industry standards, only that live (or likely to become live) wires should be brown or red (or sleeved brown or red) and the neutral should be or sleeved blue (black in the old days).
There are many more colours that can appear in a cable. In LV applications the cable should only be a live or a neutral and the installer should make this clear by the appropriate sleeving.

So, more information, thank you. Older lights did not have an internal override facility.
Many of the newer ones have waht is known as a "pulse" override function, where you turn the supply to the light off then on again quickly to enable the light to be on permanently.
If your PIR/light has this facility, then you should be using the yellow (sleeved) red wire to the live connection on the bulkhead. Then you could control the bulkhead as on, off or PIR by using the switch that has (had) the yellow wire on it. The permanent line (red) wire would not then be used, at all.

 

Thank you for you reply so far. I did mention about the terminals available in the old and new bulk head.

If I were to use Yellow (with Red sleeve) for Switched Live, then the Red Live (un-swithced ) would be left not used at the bulk head end. Would you recommend using an electrical tape to insulate the Live Red or a terminal connector to ensure it is safe? Bear in mind, this way the bulk head will have no earth. Where as now I do have Red Switched Live going to Bulk Head and a spare Yellow to provide earth.

 

They did.

They didn't.

That's the same as saying "If I had just connected it up without bothering to find out which conductor was which then there would have been no switched live to the light."

That's the same as saying "I could have totally ignored the industry standards and connected a cable with an arbitrary colour which was not that of an earth conductor to the earth terminal of the light."

I do not think that you will find many takers for the suggestion that connecting live to the exposed conductive parts of an outside light is "not a disaster but not ideal".

 

Then make it unused at the source end as well. Or better, make it the switched live.

The latter. Plus disconnecting it from any supply.

For what reason are you not using the cpc in the cable for its intended purpose?

 

Bas, Iam impressed by you show of diplomacy here !

DS

 

• [wiki]Electrics%3Abooks[/wiki]

NOTE: - it's been a while since that list was last updated - if you find any broken links please let us know and someone will fix them.

Also, there is a lot of stuff on the internet.

• http://www.google.co.uk/search?q=uk+house+wiring+(basics+OR+101)
  
  
• http://kevinboone.net/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html

 

Thanks for the links BAS. I will take a look once I finish work.

I have used Red, converted it to Switched instead of using Yellow. Yellow spare is now used for Earth and the red sleeve removed.

CPC? As said I am not an electrician, not sure what it is.

Note: I did bother to check everything and not ended up dead or calling fire department. Thanks to line tester and strong science background


I am not trying to stress that it was done right or wrong, perhaps 18 years ago it may have been a standard practice. I am here to find what are the recent standards and regulations. I would still insist using Yellow/Green, even with the Red/Blue sleeves, for Live or Neutral is not best practice. I would rather spend a bit extra time and money and use 4 core cable for such requirements and leave the Yellow/Green alone for what it is meant for i.e. Earth.
These basics are taught in the schools and me being nearly 40 years old, clearly remember it, I was. It is globally accepted that yellow/green means earth. Not that I am saying one should not check. If in doubt call a qualified professional. It is not worth saving any money which puts lives at risks.

 

Pay attention to the wiring. The cable will have been 3C+E. It was NOT yellow/green, it was plain yellow which was indicative of a phase conductor.

 

And what colour sleeve put on?

But why are you not using the earth conductor in the cable? That's what it is for.

Sorry.

Circuit Protective Conductor.

Good.

But that means that "I could have supplied Siwtched Live to the internal metal plate" wasn't really true. You checked, and therefore you couldn't have done that.

It's more than just "not best practice".

But it's not what you had - it was yellow which was used, not yellow/green, and yellow is (well, was at the time it was installed) a standard line conductor colour.

 

@aptsys You are spot on. It is indeed plain yellow not yellow/green. I am pretty sure I could'nt see the Earth wire though at the bulk head end. This should be uninsulated wire under the external sheath, isn't it? I guess it must have been cut short as the old bulk head didn't have earth terminal?

I will double check later today if it is cut short, if not I will swap the connections around.

It all makes much more sense now as to why it was done the way it was done.


Many thanks everyone. You have been very helpful and it has been very informative.