# Spur off a spur. Check my logic...

#### BonfireMan

It's not what you think! I don't want to do this - I think it's already been done for me.

Peruse the diagram: concentrate....

There are three rooms involved here: the kitchen and two bedrooms (between which I an rebuilding a stud wall). The temporary junction box (circle with JB) is taking the place of an original socket (in that wall I'm rebuilding) and has three cables (the red, green and pink lines) running from it.

In one bedroom (top) I have a socket with two cables which I have been using to test the ring is live using a storm lamp. Then we have two other sockets, one in each bedroom, with a single cable each; obvious spurs then.

Lastly we have a kitchen socket which has two cables, the blue and the green cables - so you would assume this this is on a ring, wouldn't you?

The diagram is loosely based on how the cables are under the floorboards; specifically the sockets they head off towards.

I wanted to work out which of the cables I can see was the one that went off to the spur, so I could add a new socket to the ring in my shiny new wall (which would only involve another 2m of new cable). Thinking the green and blue cables *must* be part of the ring I disconnected the pink cable, but all the sockets continued to work. So, I disconnected the red cable, but all the sockets *still* continued to work. uh...

So I disconnected the green cable and the "southern" spur stopped working! All the other sockets still worked too *except* the kitchen socket. Now, the only way that could happen is if the blue cable (connected via the green cable and the kitchen socket) went to that spur. Now, if the blue cable *were* part of the ring the kitchen socket would still work, yes? But with the green cable disconnected it doesn't.

So, it looks like the original house wiring includes a spur off a spur. Or is my logic floored...

Share your wisdom. Ta.

(FYI: I pulled up a few more floor boards in the "northern" bedroom and the "northern" spur is fed off the red cable via a junction box. The ring continues off toward the other socket in that room. There used to be another wall in the kitchen below, so I'm assuming there was a socket down there which was part of the ring and is now replaced by the Junction box. The only other plug socket upstairs has two cables so I assume is part of the ring; it's in the general direction the pink cable is off to. Yes, a couple of assumptions there, I know.)

#### plugwash

From your tests it does indeed seem to me that the green cable goes to the southern spur.

can you disconnect the blue cable from the kitchen socket and reroute it to somewhere on the ring?

#### Taylortwocities

Before you take any further steps you need to check your assumptions.

Just because a socket has two cables going into it does not make it part of a ring. It may be a spur with another spur off it. Or the circuit may be a radial.

First off: The suspect ring circuit. How many cables going to the CB in the fuseboard? and what is the value of the MCB?

Next: you will need a voltmeter or a mains test device.
turn off the power, take the two live conductors out of the back of the socket. Keep the kids and dogs etc away from the area.
Turn the power back on and test from neutral to each of the live ends of the cable. If you have live on both cables then its likely you have a ring. If not then you have aradial or an illegal spur+spur.

Turn power off and put the cables back.

Then let us know what you find.

#### securespark

How many sockets are there in the property?

How many have three cables?

How many have two cables?

How many have one cable?

Two cables does not necessarily indicate a ring final.

If you feel confident, isolate the power to the house.

Identify the circuit in question. I take it there is only one socket circuit? You mention bedroom sockets on the same circuit as kitchen ones.

Taking care, open the consumer unit & disconnect the wires connected to the fuseway or MCB for this circuit. How many are there?

If there are two or three, separate them. With a multimeter set to resistance, check what readings you get between the wires.
If there are 3, test between wire a and wire b, wire a and wire c and wire b and wire c.

If it is a ring final, then you should get a reading other than open circuit.

However, this does not tell you how many sockets actually form part of the ring final circuit. This can only be ascertained by futher more complex testing.

If you don't get continuity between any of the wires, or if there is only one wire present, then you have a radial circuit. Depending on the thickness of the wire & the size of the fuse or MCB, this may be a dangerous situation.

EDIT: I type too slowly...

#### rebuke

Also, as a general note in case you aren't aware - assuming you're talking about a traditional screw type junction box, you imply that the one for the northern bedroom is under a floor - it shouldn't be, as the regulations state they must be accessible for inspection, testing and maintenance.

Obviously, you didn't put it there, so not your fault, but if you can when dealing with the situation find any way to replace it (e.g. use crimps with a proper ratcheting crimp tool), or create an extra socket instead of the JB or whatever, it would be good...

#### BonfireMan

securespark, taylortwocities: Thanks for that advice. Not sure how keen I am to mess with the consumer unit. Or connect live to neutral with a multimeter! But I may know a man who may help out there.

It's a bit too late to check tonight (I'm surprised to get a reply so soon!) but I believe there's two cables running to the consumer unit. Quite sure it's a ring: one, I was told by a sparky one time; two, when I disconnect all these cables all the sockets stay working (don't worry, I place boxes on the ends - no floating live cables here).

There are two rings: the original ring for the whole house and a new one for the kitchen. There's one socket left from the original ring still in the kitchen though, which is the one we're talking about.

There are nine sockets on this ring (including (this kitchen one and my temporary junction box). Only this one has three cables. Only the two spurs on my diagram have one cable. The rest have two cables.

All the cable (that I can see) is 2.5mm. The MCB is 32A.

plugwash: no I don't think pulling the blue cable from the kitchen socket is an option.

===

Hm, what to do? I'm supposed to have the plasterboard on tomorrow and the floorboards with all this underneath need replacing first as they're to pass under the wall. Argh! I see two choices: lose one or the other of the kitchen socket or "southern" spur, or leave yet another junction box under the floorboards that spurs properly.

(I'm off to bed now. Wot no sleepy face?)

#### BonfireMan

rebuke: thanks for that. The floor will be bare in that room for a while so I'll look into changing that. It might also help my current problem too.

night night.

#### plugwash

how about removing the pink cable from the "temporary jb" and connecting it to the "south spur" socket?

#### BonfireMan

That makes sense but the pink cable will not reach that socket so a JB would still be needed (and I'd have to lift even more floorboards and run the cable through the joists to get there too).

I was thinking this:

Cut the blue cable and link with the pink to make a circuit and a proper spur. Does that make sense? But I need to be *sure* I'll get the circuit I want - there's still a tiny doubt in my mind I can't ignore - and it'll need to be crimped rather than be done with a junction box as it won't be available for inspection.

#### BonfireMan

Is this what I need to crimp the wires together rather Junction Box them? http://tinyurl.com/ae3yez

What about the actual crimps? I can't find them! The colours and sizes don't make sense. For example I was expecting to see brown, blue and green in 2.5mm and 4mm etc. http://tinyurl.com/dfcv3z

And after a bit of reading it seems they need to be double "heat shrunk" too (to provide double insulation like the original cable)? I think a JB might be better - I'll know I've done that right! How complicated is crimping? Are the tools expensive?

Is it even possible to crimp three wires together to create a spur?

#### BonfireMan

OK. I need http://tinyurl.com/byw4vd butt connectors in red and blue; red for the earth and blue for the live and neutral. Like this:

It seems I don't have to heat shrink as long as it's in trunking but it won't be as it's under floorboards! I can't see a way to do a three way crimp to provide a spur so it would mean losing the spur in the bedroom.

Is leaving a JB under the floorboards OK as long as the floorboard is easily lifted for inspection?

#### BonfireMan

OK, here's what I'm thinking the solution is:

The red and the green cables don't get touched. I cut into the blue cable and junction two new cables in (temporary - they will be crimped later on but it'll get me moving on finishing the wall) up to a new socket next to the original one (currently in a temporary junction box). The pink cable will then run from this new socket instead of the old one.

So the ring will now run through red, green, blue and pink. The spur will be OK and the kitchen socket on the ring main for the first time in it's 38 year history.

Anybody see any issues with this? Am I right in thinking that the crimps won't need heat shrink as long as they stay in the junction boxes? (You are still there...?)

#### Taylortwocities

Crimps are only good for through connections. You cannot get a good reliable connection for a spur - eg two in and one out.

Much better to do that sort of thing in a deep box behind a socket, or have a box in theh wall with a blank plate over it. Then its accessible and you can use terminal strip.

You are still there...?)
Its Sunday morning - most of us should be listening to Sunday Lovesongs with Mrs Sparks......

Not me though, Mrs TwoCities has flapped off to New York for a week - at half term too.
I hope she's back soon - the washing up is really getting in the way of the motorbike rebuild in the living room....

#### RF Lighting

most of us should be listening to Sunday Lovesongs with Mrs Sparks......

I'm not sure how Secure would feel about that if he found out

#### BonfireMan

Sorry, "you are still there" was supposed to be a funny though it doesn't look like it now I look back. I was thankful to get replies last night never mind this morning.

I've abandoned the job till next weekend while I gen up and practice crimping. I'll just have to live with the mess till then!

I can also get someone to check that it definitely *is* a ring main I'm working on here. I don't expect otherwise but then I didn't expect a spur off a spur either, did I?

I might also be able to get that kitchen socket integrated into the kitchen ring main too, if I can crimp. Which would be nice.

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