Lighting circuit

[Scott]

Simplistically, am I right in understanding that a lighting circuit is linear (not a ring main)? All the action takes place on the red (*) wire. In each room there are two drop cables: one to the switch and one to the light fitting. The electricity goes from the ceiling to the switch then back to the light fitting (via the black) then through the light bulb to the main black wire. The same is repeated in each room.

This means only one cable is connected to the consumer unit. I believe a red sheath should be fitted to the black wire at the switch.

(*) Although I refer to red and black, I appreciate these may be brown and blue. I have ignored the earth but I assume every earth should be connected to every other earth at every opportunity.

[The Natural Philosopher]

Yes

Yes

Yes ot no depending

No.

In genereal the cable goes from te curcuit to the stich, and then on again to the next swich and cables are run from te switch to te light fitting. So the switch has THREE cables entering it.

Even if te light fiffing istelf carries the nain circuit it is coinventional to run TWO cable to the switch so as NOT to have s bcak wire being swtiched live.

Yes

I

I believe its not done like that in best practice, I never have.

In the limit you need to carry live, switched-live and earth to the switch as you have surmised, but I do not think that normal T & E colors are used in that case.

[Robin]

"Loop in" wiring is AFAIK (a) dead common, (b) still perfectly acceptable and (c) what the OP seems to have.

[FMurtz]

In Australia generally, because all lighting for quite a while has to have an earth present they mainly run a twin +E through every light point (A N E )and then drop a twin down to the switch from each point for standard lighting points.

2 way requires a wire between switches. Rarely do you need a neutral at the switch point

[The Natural Philosopher]

I am amazed.

[ARW]

There are various ways to do lighting

it is though just usually a radial from the CU.

[newshound]

I think you mean NO

[Brian Gaff]

Ahem, there are always live and neutral in all my ceiling roses even if the switch is off, and to me this disproves your hypothesis completely

[Brian Gaff]

You obviously have a keyboard like mine with a couple of sicky eys Brian

[tabbypurr]

Pretty much. The other way to do it is run the T&E from the CU to each switch, then T&E carrying E, N, switched L to the light fitting.

NT

[Scott]

Depends on your interpretation of my hypothesis. When I said the action takes place on the red, I did not mean no return path was needed. I do have some clue about electricity. I meant the 'diversion' and switching takes place on the red.

[John Rumm]

Erm, yes! That's the way most loop-in systems are wired. Ideally with some coloured sleeving over the neutral wires where they are being re-purposed as switched lives.

That is another method ("switch loop in"), but its far less common.

That's even less common (to the point I have never seen it done)

Its is a regs requirement, since you are using a wire for a purpose its colour would not indicate otherwise. I will agree its frequently missing however, but it should be there.

You can get a T&E with two red/brown conductors, but its rarely used since normal colours and over marking is acceptable.

[bert]

Would you believe I have both in my house. The old original part is L and N to the ceiling rose. The extension was wired to the switch. Done by a fully certified electrician of course - well actually done by his apprentice, about the same standard as Adams. I had to go round a tighten up at least 3 connections within the week.

[ARW]

Becoming more common all the time.

[Scott]

Why are there several ways to wire a lighting circuit when there is only one way to wire a ring main?

[tabbypurr]

There are at least 2 ways to wire sockets

NT

[Scott]

Are there two ways to wire a ring main? Do you mean with or without spurs, perhaps?

[Mike Humphrey]

Because usually things on a ring circuit don't have remote switches. If all your lights have built in switches, there's only one way to wire a lighting circuit. If all the sockets on your ring have separate switches, they can be wired the same two (or three really) ways. But lights normally have separate switches, and sockets normally don't.

A simpler version is that there's four ways to wire a switch to a switched load:

1) The switch is built in to the end accessory. 2) "Junction box" wiring - the "main line" of the power circuit connects to a junction box. Live goes to the switch, switched live comes back, switched live and neutral go to the load. 3) "loop in" wiring" - the main line of the power circuit goes to the load (light) which has an extra terminal - effectively a built-in junction box. Live goes to the switch and switched live comes back. 4) I don't think this one has an official name - the main line of the power circuit goes to the switch. Switched live and neutral go to the load.

Note that two or more of these - even all four - can be mixed on a single circuit. None are more correct than the others but some are more common. Lighting circuits usually use 2 or 3, sometimes 4. Power circuits use 1, though 4 is used in kitchens (where there's a switch above the worktop and a socket below).

Mike

[John Rumm]

Perhaps a better comparison with socket circuits in general rather than a ring specifically. Then there are several ways of doing the sockets. However socket circuits are inherently similar in that they don't usually involve remote switching (save for a few under counter sockets in the kitchen), or a remote load from the main termination (although you could argue a spur is such a thing).

[John Rumm]

Probably the influence of lots of imported fancy light fittings with inadequate terminal space for traditional loop in style wiring, and demise of the common ceiling rose.

I find switch loop through quite handy for surface wiring applications, and exterior lights, where a single cable connection is neater.