Loft conversion sockets wiring...

[ChristofG]

I have somewhat of a problem with the wiring in my loft conversion which I need some advice on...

I've remodelled the room slightly which involved taking out some of the walls. During this I've found what look like 2 spurs. They come up through the 1st floor level ceiling at the exact same point and then take opposite paths around the loft room. One simply ends in a double socket and the other has a double socket that then leads on to a really ancient fused switch box (the type that looks like it would then have the flex from an appliance go into it).

I have no idea where the spurs originate from except that they are on the same Consumer Unit breaker as the 1st floor sockets. The cables are fairly securing seated in the loft floor/1st floor ceiling void aswell - so there is no way of jiggling the cable and having someone watch the ends at another socket.

My problem is that I need more than the way sockets on one of these spurs and the other socket is in completely the wrong location of the room. This is going to be a home office so really needs to have about 8 or so sockets for computer, portable and mobile phone charging, Monitor, printer, Broadband router, etc.

I beleive that the regulations for spurs is that they mustn't provide any more than 1 double socket - so this fused switch box presumably needs to come off ideally and I shouldn't really add anymore sockets to the spur where my desk will be ?!?!?

Or... is there simply a limit to the load which is permitted from a spur? If so, since most of my items will be smallish load (phone chargers... 350mA, Laptop charger... 300W Max, etc.) would I be able to get away without having to rip down ceilings and stuff to put in a new ring circuit.

ANy advice much appreciated.

 

[kevnurse]

The max load on a spur is dictated by the size of the fuse in the fcu. The fuse should be rated such that it will rupture before the spur cable overloads or overheats.

Therefore, you can have quite a few double sockets on the same spur, provided that you use a 13A fuse in the fcu and use 2.5mm cable in a ventilated area.

 

[ChristofG]

I assume an FCU is a fused (or possibly even circuit-breakered) box that I would put in the spur line as the very first item... so that if however many sockets I had coming after it exceeded the rated value the fuse/breaker would blow ... do I have that correct?

At the moment one spur has just a socket and the other has a socket followed by a fused switch but only the switch is fused... not the spur circuit.

I am pretty sur ethat the cable use is at least 2.5mm2 and so in theory that spur cable could take up to 24A Max.... is the 13A you recommend to allow a good safety margin?

Is it also practicable/safe/acceptable to joint the two spur end together to form a mini-ring? Although this would seems to spread the load in that loft ring it would effectively create a sort of figure 8 ring main (where the spur loop actually came of two points in an existing ring. Also, If I stick with just the one double socket on each spur do I have to put an FCU on each?

 

[kevnurse]

A FCU is a fused connection unit. It can be switched (often double pole), it might have a LED, but it must have a fuse. There's no reason why you couldn't create a ring, from one FCU, but there is no point. The max fuse you will be able to fit in the FCU will be 13A, so a single 2.5mm cable radial is more than enough for that rating.

If both of your cables appear in the loft through the same hole, it is quite possible that they are both connected to the same point on the ring circuit below (upstairs sockets?). You need to establish the source of power to each of those 2 cables. It is acceptable to run one cable spur, un-fused, from a socket on a ring to one other socket, only. It is not acceptable to run 2 cable spurs, in parallel, from one socket, otherwise the socket could be overloaded without sufficient protection. If both cables are joined to the same socket you should disconnect one of them and label it as a dead cable.

If both cables are independantly powered, and you want more than one socket on each spur, you should fit a 13A FCU on each and then connect your sockets (2 on each?) and run the spurs in opposite directions around the room (do not be tempted to join them into a ring). Or, if you have only one cable to play with, you can split the spur, on the outlet of the FCU, into 2 radials, each going in the opposite direction around the room.

Hope this helps.

 

[plugwash]

Finding out where the spurs come from is probablly a good idea, if they come from the same point or two points close together then it may be quite easy to modify the circuit so they become part of the ring. This would be my preffered soloution.

is there a socket below where they come up? if so have you tried taking that socket off and looking how many wires there are?

 

[dannyboi2003]

Where the cables appear in the attic from the wall below can you work out roughly what wall they go into, go downstairs and look if theres a socket on the wall below. If there is then open it up and see if your two cables are spurred of this socket, post back and let me/us know what you find.

 

[ColJack]

the load you are adding is best suited being run from a 6 or 8 way surge protected extension lead.... no need to add sockets to the spurs..

why do people do it the hard way..

I have my desktop, printer, monitor, zip drive, router, cable modem all running of one extension lead..

 

[ChristofG]

I take your point ColJack and if I hadn't uncovered what I suspect is a bit of an abomination in the wiring for my first floor sockets then I would probably take your advice and go with the simple answer. However, Whilst I was trying to do plan a thorough job of it today I've uncovered a bit of a mess.

What I believe is the ring has 2 junction boxes in the circuit. At one of the Junction boxes there are 2 additional circuits coming off it... one of those two goes up into the loft as one of my existing double sockets. The other serves a socket in a small box room on the 1st floor before going up into the loft to serve the second on the 2 double sockets up there.

That means that from one point in the ring (at one of the Junction boxes) there are 2 spurs coming off and one of those spurs has both a single and a double coming off it.

Now I beleive that I could adapt the circuit at the Junction box in question and with the addition of a cable between the two loft sockets I would then turn the whole thing back into a true ring (except for the single socket spur coming of the other J/Box but that should be fine to leave).

I was going to try and draw up a diagram of how the circuit is now and what I intend to change in the hope that one of you fine fellows might double check my logic is sound... but the first question I have is... in a ring main does it matter if some of the cables are multicore (I suspect 4mm sq.) whilst others are solid core 2.5mm sq. ??? Whoever put this in has done so with a number of the cables being the lower grade solid core.
The 2 cables from the main consumer unit are both the thicker multicore but the two cables to the loft and 2 other cables elsewhere are the 2.5mm sq.

Since ring mains are designed in 2.5mm sq I'm guessing I don't need to worry about the mix but a confirm on that would be great...

As for the diagram... I have a PDF of the layout here:
http://boldvisions.co.uk/2 Gordon Road Electrics.pdf

so... you can see the messy bit coming off JB1 and my intention would be to remove cable C1 from JB1 (aswell as the short stub of cable going from JB1 to S1) and either put C1 directly into S1 or use another junction box if the cable isn't long enough. Finally complete the ring by joining the two sockets in the loft together (as per the dotted black line.

Any colouring of cable is purely to differentiate where there are crossovers. Also I know I need to limit the total cable run... what is the limit for a ring main? Does my question about mixed cable gauges make a difference? In a ring circuit does that 'total length' I've seen quoted elsewhere mean from where one cable leaves the CU to where the other returns to CU or does it mean length to the centre point of the loop?

Any advice, answers and logic checks would be greatly appreciated.

 

[ChristofG]

Anyone got any advice or a confirmation that my logic is sound?

 

[Adam_151]

As to the stranded cables, theres two explanations, these days T&E of size 2.5mm² or smaller is solid, whereas anything bigger is stranded

The other one, is it could be imperial cable of size 7/0.029 which was the imperial equiv. of 2.5mm² (if the strands are silvery then this will be the case; tinned copper)

What you say seems ok, from what I can visualise, if you could scribble it out in paintbrush; that would make it easier, from the way I read it, you have two JBs, and two spurs from the first, and nothing spured from the second? is that right?

 

[ChristofG]

I put a link in to a PDF file with the diagram... in my last major post above... Is PDF OK?

I have 1 spur of one of the JBs and 2 spurs of the other JB. However, that second JB with the 2 spurs has one of the spurs feeding a single socket and then onto another double.

My diagram shows where I reckon I could split the spurs and with a third JB create a full ring main again... albeit with a couple of spurs of different sockets/JBs in the ring.