Light Switch Wiring (Not a DIY Question).

[Maroochydore]

Something that has puzzled me for years.

Light switches are wired with a red and a black cable (and sometimes the earth for where a metal facia is used) but both are actually live, so technically red. It seems obvious to me that this is an easy option, sparky has a coil of cable putting a ring down so why not just use what's to hand to connect the switch into the live circuit.

However, given the number of light switches being installed, why has no one produced a red/red (and earth) cable?

Also, why is it thought regs are not required for something that could confuse ?

I realise if you don't know what you're doing you shouldn't touch electricity but swapping out a light switch is one of the simplest of tasks and everyone has to learn somewhere.

[Itsallaguess]

Also, why is it thought regs are not required for something that could confuse ?

It's because of the potential for confusion that regulations are required in this area...

Where 'Switch wires' are used like this, and a neutral is going to used as a 'switched live' for light-switching circuits, then each exposed end of the neutral wires inside the switch back-boxes should be sleeved with brown (old red) sleeving, so as to indicate, for this particular wiring use-case, that it's a live wire and not a neutral...

Cheers,

Itsallaguess

[jfgw]

The current colours are brown and blue — the same as flex. Twin brown is available for wiring switches: https://www.tlc-direct.co.uk/Products/CA1BR.html. One problem with this, however, is that it is easy for an electrician to grab the wrong reel and run twin brown instead of brown/blue. Putting a piece of brown sleeve over a blue wire is no big deal and I would consider this to be far better than using blue sleeve on one of the brown wires of twin brown. (It would also be necessary to determine which brown wire was which.)

Using blue/brown for a switch is normal. The only significant downside that I can think of is that the little piece of blue sleeve can fall off so a meter may be required to determine which cable goes to the switch.


Julian F. G. W.

[pochisoldi]

50m of 1.5mm2 twin brown+earth costs £32.19 at Screwfix, won't replace standard twin and earth, and sits in the van unused most of the time (tying up working capital).

50m of 1 5mm2 normal twin+earth costs £31.09 and can be used for a switch drop.

(Yes I know a sparky would buy 100m reels, but Screwfix didn't have identical but different coloured products available in 100m lengths)

[Mike4]

50m of 1.5mm2 twin brown+earth costs £32.19 at Screwfix, won't replace standard twin and earth, and sits in the van unused most of the time (tying up working capital).

And more importantly for the mobile tradesman, tying up precious van space. Also represents extra weight to pay to lug around, and more bait in the van encouraging scrotes to break in and steal the contents with all the consequential inconvenience.

The 'working capital tied up' aspect is less significant nowadays as electricians are reputed to be totally minting it....

[csearle]

And just to add my voice to it all (as a practising electrician)...

Light switches are wired with a red and a black cable (and sometimes the earth for where a metal facia is used) but both are actually live, so technically red. It seems obvious to me that this is an easy option, sparky has a coil of cable putting a ring down so why not just use what's to hand to connect the switch into the live circuit.

I agree entirely with what others have said. It's bad enough carrying around the large assortment of cables one needs as it is without having yet another one just for switch-drops.

However, given the number of light switches being installed, why has no one produced a red/red (and earth) cable?

The cable you describe is installed all over the place, especially in housing estates. Almost always red/red rather than brown/brown.

Also, why is it thought regs are not required for something that could confuse ?

As has also been said the matter of identification of the conductors within a cable is indeed included in the wiring regulations (used to be in Table 51).

Where 'Switch wires' are used like this, and a neutral is going to used as a 'switched live' for light-switching circuits, then each exposed end of the neutral wires inside the switch back-boxes should be sleeved with brown (old red) sleeving, so as to indicate, for this particular wiring use-case, that it's a live wire and not a neutral...

Just as a point of terminology it's the blue-insulated conductor that is being used as the switched-live rather than the neutral. Also both the line (brown-insulated) and the neutral (blue insulated) conductors are considered (and called) "live" wires because they both carry the load current.


Just as a general point, perhaps of interest, excluding wireless switches (powered or energy-harvesting) and smart systems (which often use twisted-pair data cables for their connections, there are three common ways of wiring up lighting circuits using twin & Earth cable. All three are found in domestic installations:

1. The feed from the consumer unit/fuseboard is taken (usually in a daisy-chain arrangement) to each ceiling rose with a switch-drop to the associated light switch (the connection arrangement within the rose is called three-plating),

2. The feed from the consumer unit/fuseboard is taken (usually in a daisy-chain arrangement) to each switch with a switched sub-circuit to each light fitting, and

3. The feed from the consumer unit/fuseboard is taken to an RB4 (type of junction box) from which cables are taken to each switch and each light fitting.

I personally almost always use method two for new-builds/refurbs because all the connections can be made at a convenient working height and it keeps the connections at the light fittings as simple as possible, which can be important if there is very little space in the fitting.

Chris

[csearle]

The 'working capital tied up' aspect is less significant nowadays as electricians are reputed to be totally minting it....

Not all of them. C.

[richlist]

Elvis Presley, George Harrison & Rowan Atkinson didn't do to badly.

[stewamax]

The change in wiring colours in 2004 to conform to European standard was bonkers from a purely UK point to view (OK, we had to import electrical appliances but we didn’t import out house wiring). Perhaps it was to protect any wirer with red-green colour blindness, although anyone with blue-yellow colour blindness might be a bit confused by a green-yellow earth
At least we kept our mechanically-shielded 3-pin plugs; anyone remember the prevalence of the lethal two-pin jobbies that were wired either way?

Anyone who has undertaken wiring in an awkward dark space will know of the possible confusion between brown Line and blue Neutral, especially if the blue is not a glaring blue.

Single phase Line before 2004 was red – danger – stop – watch out – fire – hurt you etc
Neutral was black.
At least earth stayed Green + Yellow; before 1977 earth was Green and even earlier was bare (unsheathed) wire.

Rant over!

[88V8]

At least earth stayed Green + Yellow; before 1977 earth was Green and even earlier was bare (unsheathed) wire.

And not only bare but in the old days if a junction box was rather full, quite often the earth wires used to be run around the outside of the box and just twisted together.

If I'm adding to an old-colour circuit, I still use old-colour cable, of which I have a decent supply.

V8

[chas49]

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(chas49)