Multiple socket's options

[voithkingsley]

Hiya all,

Let me just get straight to the point, my flat/maisonette has a ring final for all the the sockets in house, and another for the kitchen sockets, both are terminated into one 32A (If I remember correctly) MCB with RCD protection all inside the CU.

Due to the shortage of sockets in one of my bedroom's where I have my computer's and audio equipment, I plan on adding about 7 new double sockets too the room all close to each other. But with CURRENTLY no more than an 13A load on all of them at the same time! I know I will be plugging in many electronic devices but they pull just below 13A as they currently are set up.
I am just looking for advice on the best way to do this really and want you opinions.

1) I was going to tap into the flats ring main as it is easily accessed from the loft and just extend the ring main to the new sockets but after hearing "controversial" tales that the new bunch of sockets could end up pulling an uneven load on one leg of the ring, especially as they will be all close together on the wall.

2) I was going to add a 13A fused spur to the ring via an accessible junction box in the loft and then have the fused spur downstairs on the bedroom wall next to the sockets where I can change the fuse easily if I ever needed to. Then just run the sockets from that, if ever my load ran about 13A, the fuse would blow.

However I was thinking what if I ever wanted to pull a few more amps from the sockets in the future? I do plan on upgrading some stuff and this is very likely to happen. Then my fuse would keep blowing and render the Fused spur installation useless.

3) I was going to add another ring from the CU too this bank of sockets in the bedroom, would be the 3rd ring attached to the "Sockets" MCB/ RCBO along with the rest of the house as it is and the Kitchen. And their is no space for another MCB to create a separate circuit (If i remember rightly).

I was just looking for an opinion on this really and your thoughts.

Also one last thing... I will be using 2.5mm cable, I know this limits me from creating a Radial for my new sockets but I have reasons why I would prefer to use 2.5mm instead of going out and buying more cable for a 6 mm Radial. Not too mention all the data cables that are going to be in the same Trunking!

 

[ericmark]

Much depends on your ability and equipment.

Before extending a ring circuit you need to measure either the resistance with a low ohm meter (Has to draw at least 200ma and measure in 0.01 increments i.e. not a simple multimeter) or the loop impedance again an expensive tool to see if by adding extra under fault conditions it will still trip.

With FCU although you should still test the likely hood of it not having the loop impedance required is slim.

If it were me I would plug in earth loop impedance tester and if within limits then extend ring. If not then FCU it is.

Before starting I would test a couple of sockets with loop impedance meter and note reading. While doing work I would check there is a ring on all three wire pairs. On completing again reading with loop impedance meter. That way should a wire become disconnected while putting socket back then the high loop impedance would alert me of what had happened. I have adaptor to measure both Line - Earth and Line - Neutral.

This all takes seconds so likely some one watching would not even see I had done it.

But your not me and likely you don't have the knowledge or equipment. But again you might! So I can't possibly say what is best for you.

 

[JohnW2]

...I plan on adding about 7 new double sockets too the room all close to each other. But with CURRENTLY no more than an 13A load on all of them at the same time! I know I will be plugging in many electronic devices but they pull just below 13A as they currently are set up. ...
1) I was going to tap into the flats ring main as it is easily accessed from the loft and just extend the ring main to the new sockets but after hearing "controversial" tales that the new bunch of sockets could end up pulling an uneven load on one leg of the ring, especially as they will be all close together on the wall.

So long as the total is not appreciably more than 13A, the situation would be no different/worse than having just one fully loaded socket, so I would not worry about the concentrated 'point loading' on the ring. Furthermore, the issue to which you refer (uneven loading of legs of ring) only arises if one is fairly close to one end of the ring. If the group of new sockets was near the mid-point of the ring, there would be no such problem at all, no matter how much current was involved.

2) I was going to add a 13A fused spur to the ring via an accessible junction box in the loft and then have the fused spur downstairs on the bedroom wall next to the sockets where I can change the fuse easily if I ever needed to. Then just run the sockets from that, if ever my load ran about 13A, the fuse would blow.

If the total load is already close to 13A, and may well rise in the future, I don't think that this would be a good approach. Bear in mind that a 13A fuse will allow a fair bit more than 13A before blowing. You could, of course, have two or more fused spurs (say, one serving 3 sockets and the otehr 4 sockets). However, extending the ring is undoubtedly the better solution. Also note that the FCU would need to be fairly close to where the spur joins the ring - certainly no more than 3m.

3) I was going to add another ring from the CU too this bank of sockets in the bedroom, would be the 3rd ring attached to the "Sockets" MCB/ RCBO along with the rest of the house as it is and the Kitchen. And their is no space for another MCB to create a separate circuit (If i remember rightly).

That's probably the best solution of all - particularly given that the 13A (currently) to which you refer probably isn't the only load on the present ring, so I wonder how heavily loaded it is in total. However, if you do not have space in the CU for an additional MCB, that's obviously a problem, and the only way you could do it (without having the CU replaced with a larger one) would be to have an additional 'mini-CU' added.

Also one last thing... I will be using 2.5mm cable, I know this limits me from creating a Radial for my new sockets but I have reasons why I would prefer to use 2.5mm instead of going out and buying more cable for a 6 mm Radial. Not too mention all the data cables that are going to be in the same Trunking!

Extension of the ring or a fused spur would only require 2.5mm². Electrically speaking, a 'radial' unfused spur in 4mm² whould be OK, but there is discussion about whether this is actually 'allowed' by the regulations. One reason for this uncertainty is your first point - the need for a 4mm² unfused spur implies a consdierable 'point loading' on the ring.

Kind Regards, John

 

[sparkybird]

I would certainly not try to do option 3 - shoving 3 ring circuits (6 cables) into 1 circuit breaker is not good practice - in fact doubling up as you have already got isn't either, but I guess someone's added a circuit to a board with no spare ways so shifted the one of the rings to share

Also you're not allowed to run data cabling in same trunking as mains voltage cables, unless it's compartmentalised trunking

 

[JohnW2]

I would certainly not try to do option 3 - shoving 3 ring circuits (6 cables) into 1 circuit breaker is not good practice - in fact doubling up as you have already got isn't either, but I guess someone's added a circuit to a board with no spare ways so shifted the one of the rings to share

Indeed. Looking at what I wrote previously, I see that it might not have been clear. When I talked of 'option 3' being the best, I was thinking of a new ring with its own MCB, acknowledging the problem mentioned by the OP about there being no spare capacity in the CU (and offering a possible solution) - i.e. I was essentially talking about the last sentence of what he had written.

I must confess that I hadn't noticed that he said that he thought the existing ring and the kitchen ring shared the same MCB. That's clearly not a very good idea to start with, and to add a third ring to that MCB would be pretty crazy, both from the point of view of loading and, as you say, the issue of trying to terminate 6 conductors in one MCB. I wonder if he's right about the shared MCB - if it is, it could well be that he could do with a new, bigger, CU, which would solve the other problem. Voithkingsley, are there really 4 wires already going into that one 32A MCB?

Kind Regards, John

 

[voithkingsley]

Thank you all for your fast response!

I have taken all your advice into careful consideration and will continue to do so.

I was able too get over the the flat and get a ladder up into the loft and have a long more detailed look about. Also I was able too move all the junk from CU cupboard! ('') and have a look inside. And it turns out my memory is wrong!

The CU has only one ring on the "sockets" MCB, so my previous comment about 2 ring's are indeed incorrect - thankfully! Only one pair of 2.5mm² wires are terminated and trace back too form the whole ring.

It also turns out that the ring also serves 2 unused sockets in the kitchen. The fridge / freezer and boiler via two separate switched fused spur's.
Their is actually an additional MCB serving a radial that feeds a double socket and switched fused spur after that, which supply's the washing machine.

It also turns out that their is room for one more MCB on the non-RCD protected side inside the consumer unit.

I have closely examined the entire ring load and can confirm currently it is serving 2 single sockets for fridge and freezer, and 8 double sockets around the building.
Which only 4 of are only ever used at one time. Have had a round estimate and done the maths a reckon the approximate continuous load when everything is on and blazing away for the ring final is about 14A, with most of the load being in the centre. Obversely less usually and during the day, and in fact most nights, the only load will be the boiler and 2 small computers. Quite a bit more when I temporarily plug the Cloths Iron in. But that's rare!!

But overall the sockets are quite "un-loaded" and the rings 2.5mm² cable is completely in free air and not in or under any any insulation throughout all of it's run's in the loft.

Also I would like too take the opportunity too kindly ask, if it's stated that I need too run any additional main voltage cables in separate trunking, does this mean that I need to do the same inside the loft? Obviously I don't plan on placing them directly on top of each other. (I was thinking about making the extra effort and doing this anyway, as I don't want too end up with a mass of crosstalk on my data cables)

Plus are Coaxial cable's considered data cables? I know they practically are, (all mine are just for TV distribution) but I am yet too hear about and experience any severe problems resulting from Coaxial cables being run too close too Mains voltage cables. Although I'll probably just go ahead and screw up another piece of 25mm trunking just for currently data wires anyway!