Three cables to/from a socket - does it always mean a spur?

[smp50]

Hi. I've got some floorboards up in the front bedroom of my two-bedroom house and have mapped out all of the wires. The vast majority are, I'm fairly sure, for the lighting (downstairs ceilings and switches, plus landing light and switch), and these are all to one corner of the room.

I identified ONE cable originating alone from another corner of the room directly above a socket downstairs, and this runs across the room and heads directly for the only socket in that room. I lose sight of it a few floorboards from the wall, so there's uncertainty - but there isn't really anywhere else for it to go. Behind the socket facing, I find THREE cables - all wired in as you'd expect (L+L+L, N+N+N, E+E+E). Two of them enter the mounting box through one hole, and one through another.

So my first thought was that there's a spur taken from this socket to somewhere else, right? Now, there is only one other socket in the whole of the upstairs, and that's in the back bedroom, only a few feet away from the socket in the front bedroom, through some walls of course.

Behind that socket, in the back bedroom, I was expecting to find ONE cable - if it was on the spur from the front bedroom. But in fact there were three again!


So to summarise, upstairs has only TWO plug sockets in total; one in each bedroom. Both of these are wired with THREE t&e cables each.

Can you please suggest what this could mean? Must there be a spur coming from both of these sockets? If so, I can't think where they go to! I haven't mapped out the downstairs electrics yet so it's possible that these two upstairs sockets each send spurs to downstairs sockets. But that seems pretty strange to do.

Or is there alternative explanation?

Thanks,

 

[PrenticeBoyofDerry]

It could be that the bedroom sockets are spurs for sockets downstairs.
A few alternatives are power to loft, boiler, wall lighting, outside lighting, alarm system.

 

[bernardgreen]

If you have a solid ground floor the person who wired it probably took the easy option to run a ring around the first floor sockets and drop spurs down to the sockets for the ground floor. Easy as it avoids having to chase out channels in the solid floor, walls are easier to chase.

 

[smp50]

It could be that the bedroom sockets are spurs for sockets downstairs.
A few alternatives are power to loft, boiler, wall lighting, outside lighting, alarm system.

Good ideas - none apply here, though, I'm fairly sure. Must be spurs, I guess.

If you have a solid ground floor the person who wired it probably took the easy option to run a ring around the first floor sockets and drop spurs down to the sockets for the ground floor. Easy as it avoids having to chase out channels in the solid floor, walls are easier to chase.

Yes, perhaps. I'll have to check that downstairs socket below the point of origin of the single cable I mentioned - perhaps that's the end of the spur, or maybe part of the ring. I'll examine all downstairs sockets to find out whether they're on a spur or not, and hopefully that will match up with what I've found upstairs.

Thanks

 

[ericmark]

Question one is does the house have rings? It could use radials. The 32A MCB in the consumer unit would show either a ring or a radial using thicker cable like 4mm.

Second is where split some houses are up/down others are side to side the latter reduces cable run so improves the loop impedance.

Testing is quite easy even with a simple bell and battery you can work out if two wires form a ring or not. Guessing is just not good enough.

Power off of course.

 

[JohnW2]

Second is where split some houses are up/down others are side to side the latter reduces cable run so improves the loop impedance.

It sounds as if there may be no split in the OP's house - just a single (probably ring final) sockets circuit, supplying the two upstairs sockets and (via spurs on drops) the ground floor sockets.

Kind Regards, John

 

[smp50]

Ok, guys - here's some more info.

Downstairs, in the original part of the house (there's an extension, I'll get to that) there are two sockets. I've identified that both of these are on spurs, so I reckon that accounts for the two sockets upstairs being triply wired. The physical location of those two downstairs sockets also matches up fairly well with the upstairs ones, and it makes sense that cables could be going between them.

As a side note here, currently one of those downstairs sockets - on a spur from upstairs - has a plug left in it which goes out to the shed with lighting and six sockets! There's some kind of large switch box out there, two in fact, and I haven't investigated that circuit fully yet. But that seems a bit dodgy, perhaps. I might send power to the shed from a different source at some point.

Back in the house - the extension contains the kitchen, bathroom and a hallway. Aside from lighting, there's a shower with switch in the bathroom, and three sockets in the kitchen. Based on the old CU, right now I'm guessing that the ring main includes three kitchen sockets (they're double-wired, so not on or sending spurs) and two upstairs sockets (each of which sends one spur back downstairs).

I will investigate further to establish the order or sockets in the ring.

 

[phatboy]

That's a serious lack of sockets! Sounds like quite an old house, so therefore I would guess it needs a rewire? Not that there is much to replace!

But I bet you want a lot more sockets than that!

Does the lighting circuit have a CPC in it? (This is all assumptions of age based on the lack of sockets)

 

[smp50]

That's a serious lack of sockets! Sounds like quite an old house, so therefore I would guess it needs a rewire? Not that there is much to replace!

But I bet you want a lot more sockets than that!

Does the lighting circuit have a CPC in it? (This is all assumptions of age based on the lack of sockets)

It's only a 1930's ex-LA place, not "old" as such. The cabling seems in good condition from what I can tell, but what do I know? The copper is all still shiny and bright, anyway, and the sleeving is intact.

The previous owners were elderly and it had been decades since they had their family living there, and I suppose then wasn't a time of numerous electronic devices anyway.

I plan to put two more sockets in each bedroom by extending the ring. The current route of cables in the pre-drilled joists lends itself very well to this and I should be able to do it quite simply. I'll need to look into how I can join cable end-to-end safely and "legally", though.