Upstairs ring main has 2 loops

[efj]

Hi,

My question is trying to understand why I have two loops upstairs for one ring main....

In process of changing single for doubles and adding a couple of spurs on the upstairs ring main. I've done the following tests:
1) Fuse off on MCB (marked upstairs sockets) and every socket upstairs is without power.
2) With the fuse still off, voltage test (no power) and continuity test on 2 disconntected lives at one of the sockets (all other sockets off and nothing plugged in). Ring main.
3) With the whole main board off, continuity test on 2 live feeding the fuse - Ring main. Also tested the 2 neutrals from the corresponding 4mm cable - Ring main.

So it all looks like a ring main, but I have 4 cables running into the cavity wall upstairs which I then assume lead down to the MCB - I can't trace the cables any further. In effect giving 2 loops upstairs. The only reason for this I can think of is that the ring main was actually looped all the way back down to the MCB without actually being cut and connected to the board to allow a quick and easy way to create a 2nd ring upstairs should the need arise? Is that common practice? Or could the the two loops be joined before the MCB - there are only 2 lives on the fuse for the ring main in question? Or would this frazzle?

Thanks for any suggestions on what might be happening!

Elliott

 

[FredFlintstone]

I'm struggling to understand where you've found the four cables - it sounds like they're in the cavity wall in a room upstairs - is that correct? Or are there four cables in the cavity downstairs, all going up?

Could two of them be the cables for the downstairs ring, fed from the ceiling void down to all downstairs sockets?

Are the cables the same? Could it be that the house has been rewired and they've just left the old cables in the wall so in effect they lead to nowhere?

I know lighting circuits usually use smaller cable but could it be that they're for a lighting circuit somewhere?

You really need to find out where the go to and where they come from in order to determine what they're for.

Regards

Fred

 

[efj]

Fred,

Thanks for getting back so soon. To add some more detail...
1) The four cables are coming out of the cavity wall in an upstairs room beneath the floorboards. So they are only visible beneath the floor in the upstairs room. I can't see down the cavity or behind the mcb on the ground floor to know how far down they run.
2) The four cables are all the same 4mm twin and earth and I can also see thinner lighting cable and redundant original wiring aswell. So there has been a re wire in the past but the new stuff seems to have been done properly...
3) Probably the most important point!! Three of the four cables actually feed sockets in use and thus, from the continuity tests, I assume are on the same ring main.
4) I'll double check if the downstairs/upstairs sockets are on/off when the relevant ring main fuse is off.
5) I've assumed the 4th cable is part of the ring main - is it was easier to explain 2 pairs of cables (and the loop back as per original post) rather than 3 cables....
6) I've sketched the connections discovered to date, but left it at home! I'll add it to this post tomorrow.

Appreciate your help as I'm starting to wonder if there is something very dodgy going on.

Cheers

Elliott

 

[davy_owen_88]

Your getting ring continuity with 4mm² cable? 4mm is usually used for radials. Are you sure it is 4mm² not 2.5mm²?

If they are 4mm² then my bet is someone ran them as radials and then later on someone came along and thought... 'oh, i'll just add a bit of wire here and then I have a ring circuit, oh and a bit from here to here too. Go me.' Or something like that

What size fuse/MCB are these cables connected to? Could one of them be a radial for fridge/freezer in the kitchen? Could you post some pictures of the consumer unit and associated wiring?

Davy

 

[efj]

Hi davy,

Thanks for the help, to answer your questions:
1) I'm not 100% sure it is 4mm, it looks bigger than the 2.5mm with I bought to do the spurs. I'll take a closer look tonight.
2) Is connecting up radials to make a ring safe?
3) The ring main is on a 30 (amp or ma?) fuse at the main box.
4) All the cables I'm looking at are upstairs well away from the kitchen - which has easy access from the cellar for wiring. We don't have an electric shower. There used to be an immersion heater...ahh that could have something to do with it. Though I've not seen an immersion fuse. Would that normally be on it's own radial, on shared raidal or on a ring?
5) I'll add the photos of the box, the wiring etc tonight.

Cheers

Elliott.

 

[davy_owen_88]

Here are the sizes of twin and earth so you can confirm it is 4mm²:

1.5mm² - 8.2mm x 5mm
2.5mm² - 10.3mm x 6mm
4mm² - 11.9mm x 6.25mm

It's not unsafe to turn a radial into a ring but it's also not necessary. 4mm² will carry 30A on it's own so there is no need to create a ring circuit.

A 30A fuse will coincide with a 4mm² radial or a 2.5mm² ring circuit.

An immersion heater should be connected to it's own fuse but 4mm² is overkill for the 15A fuse it should be connected to.

Davy

 

[FredFlintstone]

I'd hazard a guess you've got two spurs off the upstairs ring.

Have you opened every socket on the upstairs ring?

Have you checked all the downstairs sockets when the fuse to the upstairs ring has been pulled?

Failing that, as someone else has suggested, two radials have been joined to form a ring.

 

[securespark]

Your getting ring continuity with 4mm² cable? 4mm is usually used for radials.

It is sometimes used for rings where cables are run in close proximity to insulation.

 

[RF Lighting]

and on long runs.

It is not unusual to see RFCs wired in 4.0mm² in commercial premises, but granted it is unusual for a domestic.




@ OP, what colour was the metal in the cable, and how old is the installation?



Just wondering if if the cable is 7/.029, with tinned copper conductors.

 

[efj]

Gents,
Thanks for all the suggestions and advice. I did some more checking last night. With the upstairs ring main fuse at the mcb off upstairs sockets off. Upstairs & downstairs lights and sockets on....and vice versa. So the 4 mcb fuses are correctly labelled up/s or down/s lights or sockets.

I measured the cable dimension as 12.5 x 6.1 - but looking at the chart even that seems a little off. The cable is grey, with red and black instulated 'innards' and the a silvery earth. The insulated cables contain 3 silver strands each - I've not noticed if it's actually silver coated copper - will check tonight. I'm not sure when the rewire was done. I've been told the main board is an old version of the first type to have switched fuses. So I think it's at least 10 years ago

I've mailed the admin people here to try and add some images to this post - if that fails I'll try and get them on the web some how.

Image1 - shows the trace of known cables so far. One of the ring main loops goes up into the attic and I assume comes back down. I think the cables A - D feed 2 sockets in the room they enter (but I'm still to follow this up) - thus completing 2 loops for one ring main upstairs

Image2 - shows the 4 cables coming up out of the cavity wall

Image3 - shows the pairs of cables running in different directions.

In hunting down cables last night I found:
1) A very dodgy looking light junction box thing (image 4)
2) A screw through a lighting cable - amazingly the live was undamaged
3) a screw compressing a plastic water pipe....

Nice.

Elliott

 

[efj]

Photos galore at:

http://picasaweb.google.com/elliottfjones

 

[Adam_151]

3 Strands? Definatly not 7?

3/.036 carries about 15A so is undersized for a ringmain (and 3/0.29 would be even worse!)

Ring mains should've been in 7/0.29


(and its more than 10 years old by quite a long shot, 1970s would be more like it!)

 

[efj]

Adam,

There were only 3 wires in the main cable - the live, neutral and a bare earth - each one (live, neutral and earth) was a collection of individual wires. It looked like 3 for each (does that make 9?) but I'll double check....

Elliott

 

[scousespark]

3 Strands? Definatly not 7?

3/.036 carries about 15A so is undersized for a ringmain (and 3/0.29 would be even worse!)

Ring mains should've been in 7/0.29


(and its more than 10 years old by quite a long shot, 1970s would be more like it!)

ring main Adam

 

[Adam_151]

RFC then, Paul (sometimes I lapse into non tech slang )