Routing ring main, through behind or below row of sockets

[phido2010]

I am currently extending the ring main in my kitchen (having already notified LABC of the work) and have a couple of questions if anyone can advise me?

I plan to install a continuous horizontal row of sockets and appliance isolator grid switches above the kitchen worktop. There are no gaps greater than a few millimeters between the 3 double mounting boxes. The ring main both originates and returns at the original socket which is located at one end of the row.

1. Which is best practice wrt to cable routing?

a.) Route the return leg of the ring under the mounting boxes?

b.) Route the return leg of the ring through the mounting boxes?

c.) Route the return leg of the ring in a horizontal channel cut immediately below the row of sockets. I realise this solution is unusual, though since the row of socket is continuous, surely anywhere directly above or below
the row is still in a safe zone.

d.) Route cable all the way down to the floor and back up again.

My concerns are:
a.) Damaging cable routed through a crowded mounting box
b.) Hiding cable below a socket box - the next chap along may accidentally screw through this cable when working on the mounting box.
c.) As far as I know, this is not standard practise so potentially suprising/dangerous.
d.) Creating unecessary plastering work for myself

2. Can anyone also advise if its ok to group the following sets of cable in each of their own plaster channel.

Channel 1.
6mm Cooker radial (10.2Kw) PLUS 2.5mm Cooker Hood ( 150Watts)
grouped in plaster for about 1.5 metres

Channel 2.
32Amp 2.5mm Ring cables (x2) PLUS 2.5mm Spur off ring to 13Amp Tumble Dryer socket. Grouped in plaster for about 1.5 Metres.

Channel 3.
32Amp 2.5mm Ring cable (x1) PLUS 2.5mm Spur off ring to 13Amp Washing Machine socket PLUS 2.5mm Spur off ring to 13Amp Dishwasher socket. Grouped in plaster for about 1.5 Metres.

Channel 4.
Central Heating Control cable and supply cables ( x 5 cables ) using 1.5mm T&E
(this was an existing circuit and protected by 3Amp FCU). Grouped in plaster for about 2 Metres.

Any thoughts much appreciated - thanks.

 

[holmslaw]

..

 

[LoveRocket]

The best thing to do would be to abandon the anachronism that is a ring final circuit and install a proper radial for these sockets.

Rings are bad, and even badder in high-load scenarios like kitchens!

 

[ban-all-sheds]

I am currently extending the ring main in my kitchen (having already notified LABC of the work) and have a couple of questions if anyone can advise me?

Given the questions, and the lack of knowledge/mistaken ideas they demonstrate, what did you tell LABC would be the way you'd ensure compliance with Part P?

I'm asking that not to make any kind of point, just recognising the reality of your level of competence, and how that might conflict (possibly seriously) with what your particular LABC's stance is on DIY electrics, what their charging structure is, and what you may (possibly unwittingly) have committed yourself to...

 

[JohnD]

is it a wooden floor? do you mind taking it up? where does the cable come from before it joins your row of outlets?

 

[phido2010]

Thanks for your reply JohnD.
Its a concrete floor - the ring cable originates from under the floor joists upstairs and is chased down to an existing socket.
I suppose my question should have been more generalised wrt to routing cable through/below mounting boxes - which I have seen used and also read is acceptable practise - but don't feel too happy about.
Any thoughts on my grouping of cables? Obviously I am trying to avoid extra chases but don't want to risk derating cables by my proposed grouping of cables.

 

[JohnD]

if it was me, I would take up the floor above, and trace the two legs that go down to the first socket. I would pull one of them up. With luck, it would be coming from the direction of the other end of the row so I could chase it down to meet the last socket in the row. It must travel in a straight vertical line to the socket box (no bends or diagonals)

If it did not reach, I would make a permanent crimped joint to extend it, and protect with heat-shrink sleeving. You must not use a non-permanent joint such as a junction box in the ceiling void.

 

[phido2010]

Thanks JohnD,
Wrt breaking into the ring, I do intend using a ratchet crimp and blue+red heat shrinkable butt crimps, then will heatshrink the lot. Unfortunately the part of the ceiling void where I would need to chase down the return leg is obscured by a hot water tank so I have to find a route for the return leg in the kitchen.
I am guessing that since nobody is responding favourably to my suggestion to route through/under mounting boxes - this must be regarded as bad practise?

 

[SparkyNinja]

can't you just stagger them, with the untouched leg through the box each time?

 

[phido2010]

Thanks widdler.
Your idea of staggering sounds good. I suppose I wanted some confirmation that passing the unused section of the ring through the back box was acceptable/standard practise before I went ahead.
Although I have worked as an electrical engineer for 30years I confess I have little experience of common practise in domestic wiring.

Having just had a look at the derating factors in the OnSite guide for electricians I think I should be ok if I apply a derating factor of
0.8 for 2 cables
0.7 for 3 cables
0.6 for 5 cables

Thanks.