Lighting rings

[Ed Davies]

I've seen a few references on here to lighting rings. Do people really mean “rings”. I thought it was normal for lighting circuits to just be spurs with, maybe, spurs coming off, without completing a ring. Am I wrong?

 

@JSHarris's reference to a break in the ring really surprised me.

Edited September 16, 2018 by Ed Davies

[Onoff]

Lighting is usually referred to as a radial circuit not a spur. That is just fed one end that radiates out from the cu.

[Jeremy Harris]

8 hours ago, Ed Davies said:

I've seen a few references on here to lighting rings. Do people really mean “rings”. I thought it was normal for lighting circuits to just be spurs with, maybe, spurs coming off, without completing a ring. Am I wrong?

 

@JSHarris's reference to a break in the ring really surprised me.

 

That circuit is an oddball.  It is a ring final, for reasons known only to whoever originally wired it up.  I strongly suspect that it's an "accidental ring" in that the kitchen, living/dining room and hall lights were wired as a normal radial, and the outside and garage lights were wired as a separate radial, with a third radial for the bedrooms, WC and bathroom. 

 

The pencilled circuit descriptions in the lid of the fuse box show that the outside and garage lights were originally on a fuse that was changed from a 5A to a 45A when an electric shower was added later.  At that point, someone also fitted a double gang two way switch by the front door, to operate the hall and outside light at the front.  My guess is that the feed for the outside lights was shifted to the least loaded lighting fuse and that circuit was turned into a ring final.  It ended up like this because, unlike all the other lights in the house, the hall lights are wired loop in switch, to the switch by the front door.  What seems to have happened is that the lines from  both former radials were connected together at that switch, but the neutral from the outside light circuit was left dangling.  This meant that the cable from the fuse box to the hall lights was also providing the neutral return for the outside light, whereas both cables were providing the line to it.

 

My guess is that it was just a cock up.  When I tested it, I saw two lines going to one 5A fuse and when I removed them and checked them end to end found they were a ring.  I then located the two neutrals from those cables and the two CPCs, and found that the CPCs were a ring but the neutral was open.  There's evidence that the combined hall and front outside light switch has been changed, probably when the front porch was removed and the front door proper moved to where the porch door had been.  A glazed panel was also added, and my guess is that this is where the front outside light switch used to be, and there may well have been another light in the porch as well.  The wall above the new double gang switch in the hall has a ridge running down it, which is where I think the new cables were chased in.  I've no idea how long this has been like this, but would guess that it was done very shortly after the house was built.  There's evidence of a lot of changes that were made around that time, the drive was turned around 90 deg to come out on another road, the garage was built (and looks identical to the house in terms of brickwork - same chap did both, I'm sure) and the bathroom was moved and a separate WC added.

 

The other lighting circuit, that feeds the bedrooms, bathroom, loft light and WC is a fairly conventional radial, on another 5A fuse, wired loop in ceiling.  The only slightly odd thing about it is that the light nearest the fuse box is actually the one at the end of the radial.  That circuit runs around in a big U shape, so the two lights furthest from the fuse box are actually the two in the middle of the wiring run.

 

Our new build is conventional, with two lighting radials, one upstairs, one downstairs.

[Ed Davies]

9 hours ago, Onoff said:

Lighting is usually referred to as a radial circuit not a spur

Ta. Knew there was a better word but couldn't think of it as I wrote the post. Still, the computer scientist in my just thinks of them all as branches of a tree rooted in a non-directed cyclic graph (the grid). Are there any reasons not to take spurs off a lighting radial?

 

Yep, house wiring doesn't take many changes before it becomes archaeology.

[Onoff]

2 minutes ago, Ed Davies said:

Ta. Knew there was a better word but couldn't think of it as I wrote the post. Still, the computer scientist in my just thinks of them all as branches of a tree rooted in a non-directed cyclic graph (the grid). Are there any reasons not to take spurs off a lighting radial?

 

Yep, house wiring doesn't take many changes before it becomes archaeology.

 

Go back far enough and I think some were wired almost like a spider's web so every light had its own radial. 

 

There's specific regs in what you might term "spurs" off lighting circuit's. You musn't for instance take two outgoing cables from a rose meant to only have one. 

[Ed Davies]

6 minutes ago, Onoff said:

You musn't for instance take two outgoing cables from a rose meant to only have one. 

That's presumably just a matter of how many cables you can fit in a hole and have attach securely? Another little box nearby with three Wagos or the like would presumably be fine?

 

Rather academic interest for my house as I plan to bring all the lighting wiring for switches and lights back to central boxes (one in each of the two lofts). Given the geometry of the house this shouldn't add that much cable.

[joe90]

Well when I had my new build wired it was done in two rings and he did it as left hand side and right hand side, I am used to upstairs and downstairs but my spark said if it’s done left and right and a trip goes you still have some light on each floor.

[Ed Davies]

Splitting into two lighting circuits (whether actually rings or not) so light can be “borrowed” if one trips seems a good idea. I have similar plans with the open-plan living room/study split between the two circuits and the hall (with the consumer unit on the side) on one but with all the rooms which open on to it on the other. Main loft with all the off-grid gubbins will have two lights, one on each circuit.

 

It's probably sensible not to mix the two circuits in a switch gang so that'll likely result in more switch units on the wall than otherwise would be obvious.

[Jeremy Harris]

1 hour ago, Ed Davies said:

It's probably sensible not to mix the two circuits in a switch gang so that'll likely result in more switch units on the wall than otherwise would be obvious.

 

That's pretty much exactly how our old "accidental ring" was created; when the front door was moved and the then owner decided they wanted a double gang switch for the hall light and front outside light, without realising that previously they outside lights had been on a different fuse and radial to the hall lights.  I'm guessing that this was done at the same time that the bathroom was changed (it's right behind what is now the entrance hall) and the electric shower was installed.  The fuse box only had 6 ways plus the cooker, so to install the shower the 5A outdoor lighting circuit was moved to the adjacent fuse and a 45A one put in its place for the shower.  It's pretty clear this was done after the initial wiring, as the shower cable and its additional CPC were just draped across the ceiling joists, whereas all the other wiring is neatly clipped to planks nailed to the roof trusses.

 

Funny how you can tell something about the personality of people who've done work.  The original wiring is really neat, almost as if the chap used a rule to space every cable clip. and inside the fuse box all the wires are in order and run in straight lines, with neat bends down to the fuses.  Makes testing a breeze, as it's dead easy to see which wires are which.  On the other hand, whoever bodged the lights and wired in the shower was clearly someone who didn't care about neatness at all, with cable just draped across the ceiling joists and the leaving off of the neutral in the switch.

[Nickfromwales]

Not a fan of the left / right split option tbh. 

The 2-way switching up / down hall > landing should be set up so if the downstairs goes you still get the landing light, and if the upstairs goes you still have the hallway light. Could be done the left / right method too, just my assumption is always upstairs lights off, use a plug in table lamp. Same downstairs with standard or table lamps. It’s a lot easier to spot an entire fooor has ‘gone dark’ imo.

in a larger house with small kids / elderly you can retro fit a 3-hour battery backup to pretty much any light fitting for a few £10’s and they can be in key ( communal ) areas to suit. I often put an ‘emergency’ light next to the fuse board in domestic rewires, and routine if the CU is in a garage or outbuilding  

[Jeremy Harris]

I have to say I prefer the "up/down" option if there's two storeys.  We have landing lights that are upstairs and downstairs in one large open hall, and they are two way switched from the downstairs lighting circuit.  That was really just the way it worked out, rather than a grand master plan - the ground floor was wired first and there are two lights in the ground floor hall and only one on the landing.

 

You can get some really weird configurations though.  Apart from the oddball lighting ring in the old house, one of the outlet ring finals had an odd split.  The house was a bungalow, with two ring finals, and ended up with half the outlets in the living room on one ring and the other half on the other ring with the bedrooms.  The really oddball one is that there were two double gang sockets about 3ft apart, one behind the TV, and one by the box where the satellite cables come in.  One's on one ring, the other's on the other ring.  I reckon it was done deliberately to catch out anyone tempted to just pull a fuse to do some work without testing that the circuit really was dead.  Glad it never caught me out in the 18 years we lived there, I found it by accident when we had the satellite box plugged into one and the TV into another.  I'd pulled the fuse to fix a problem with a kitchen outlet and the TV went off, but the satellite box stayed on...

 

(Yes, I know I should have turned the supply off, but SWMBO was watching TV and it was a question of "which is the greatest risk?")