Mini Ring Main off a Radial

[BBM8]

I would like a bit of advice please, I have a 6mm which comes direct from the fuse box which leads in to the kitchen, as far as I am aware there are no sockets on the radial part of the cable, can i run 2.5mm cabling to create a mini ring main for the plugs in the kitchen?

Below is a diagram of the circuit:

Untitled

• BBM8
• 11 Nov 2010
• 2

Many thanks

 

[JohnD]

this is the cable that supplies your cooker outlet, right?

 

[BBM8]

this is the cable that supplies your cooker outlet, right?

No this use to be connected to the socket in the kitchen which had radial connection to 2 other sockets in the kitchen. When I refitted my kitchen a few years back I removed all of the old sockets connected the 6mm to a juction box and connected the new sockets to 2.5mm cable. I was meant to connect the 2.5mm back to the fuse box but at the time there was a lot of work involved in digging up the floor boards etc so at the moment the socket are in a radial layout.

I was hoping that I can connect the end of the radial socket back to the juction box creating a mini ring main. I hope this makes sense?

 

[ajrobb]

As a novice, I can see some potential problems with this:
1. 13A sockets should not be connected if the circuit protection is greater than 32A
2. for a current carrying capacity of 20A, sockets should be limited to roughly the centre 1/3 of the ring to ensure that one leg cannot be overloaded. If the cable is installed with a current carrying capacity of 27A, sockets could start 5/32 of the way around the ring.

Please don't flame me for being too conservative, I am just trying to indicate the complexity of a properly designed ring final circuit.

 

[BBM8]

As a novice, I can see some potential problems with this:
1. 13A sockets should not be connected if the circuit protection is greater than 32A
2. for a current carrying capacity of 20A, sockets should be limited to roughly the centre 1/3 of the ring to ensure that one leg cannot be overloaded. If the cable is installed with a current carrying capacity of 27A, sockets could start 5/32 of the way around the ring.

Please don't flame me for being too conservative, I am just trying to indicate the complexity of a properly designed ring final circuit.

The connection at the fuse box is 32A, I think the wire is 6mm, though it could be 4mm. I will need to dig up the floor boards to have a look at the cable size that runs from the fuse box to the juction box.

 

[ajrobb]

Electrical work in the kitchen needs to be notified to building control (Part P).

 

[holmslaw]

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[holmslaw]

..

 

[ajrobb]

You been on the wacki bacci.

Consider MK dual gang sockets rated at 26A and first socket has 2 x 13A loads and second socket has remaining 6A, the first leg should be long enough in relation to the total ring length to limit current to its current carrying capacity. For 20A current carrying capacity (paired cables running in a single conduit in plaster), the design won't overload a cable if the first and last legs are (32-20)/32 of the total ring length (i.e. 3/8 ).

However, 2.5 sqmm T+E can be installed with a current carrying capacity of 27A. In this case, the first and last legs won't be overloaded if they are each (32-27)/32 (i.e. 5/32) of the total ring length.

 

[holmslaw]

..

 

[ban-all-sheds]

I would like a bit of advice please, I have a 6mm which comes direct from the fuse box which leads in to the kitchen, as far as I am aware there are no sockets on the radial part of the cable, can i run 2.5mm cabling to create a mini ring main for the plugs in the kitchen?

I'm struggling to understand why you don't just keep it as a 6mm² radial and avoid all the uncertainties of questionable circuit topologies and possible cable load imbalances.....

 

[ajrobb]

The OP seemed to be asking if he could just add a return leg from the last socket back to the junction box. He wasn't talking about rewiring existing sockets. I'm with BAS, if he wanted to re-wire the sockets, continuing the radial circuit in 4 sqmm or 6 sqmm might be best.

My answers are just trying to show that designing a ring is not as simple as adding a return leg from the furthest socket. As mentioned, a competent sparks could sort it out, just maybe not in the way suggested. The other advantage is that they could certify their own work and notify BC.

 

[ban-all-sheds]

He wants to add a whole bunch of sockets to the end of an unused 6mm² radial.

He wonders if he can do that by making the circuit a lollipop.

I suggest he carries on with 6mm² and keeps it as a radial.

 

[ajrobb]

I'm sorry, I missed that the old sockets have gone. Continuing the radial avoids design issues.

 

[LiamPope]

I suggest he carries on with 6mm² and keeps it as a radial.

As long as he gets accessories that can accommodate 2x 6mm² cables.