Extending Ring Main


Postby flandros » Sat Oct 04, 2008 11:37 am

I am looking to extend the ring main powering the sockets in my kitchen.
Everything I have read indicates that 2.5mm cable should be used.
However it looks as though when the house was built 1.5mm cable was used.

My first question, is there anything wrong with extending using 1.5mm to match the original installation?

My second question relates to direction of cables. At the moment the ring drops from the ceiling to a socket half way up the wall with a spur to another socket below it closer to the floor.
As a cupboard is going on the wall where the upper socket is I am planning to move it sideways so it is not behind the cupboard, change it to a fused switch to control the lower socket on the spur (which ideally is to remain where it is), extend the ring to the side of the upper socket to add a double socket and a fused switch from which I can run a spur to an external socket. The additional socket /switch are less than 50cm from the original upper socket position / drop from the ceiling.

My second question is this. Is it ok to extend the ring running cable horizontally for the short distance between the original upper socket position and the new switch for the spur and additional socket and switch? Or should I be dropping vertically from the ring in the ceiling for each individual item and move the lower socket so the spur runs directly below the fused switch?
flandros
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Postby ericmark » Sat Oct 04, 2008 3:00 pm

A 13 amp socket can be fed with 1.5mm cable but at origin, it must be suitable protected against overload. i.e. fuse or MCB. This is where the problem lies.
You would need to protect a 1.5mm ring main at 20 amp rather than the 32 amp normally used for a 2.5mm ring main.
As a radial then 1.5mm will need a 16 amp MCB rather than the 20 amp used with 2.5mm.
I would question if 1.5mm cable was ever used for a ring main? In my house in the kitchen there is a double socket which was originally the remote switch for the emersion heater and there is another one upstairs where the emersion heater was, both may be in 1.5mm (Not checked) and are protected with a 16 amp MCB and if the house did not have an electrical plan I could see how a future occupant may think this is a 1.5mm ring main! When instant gas hot water was installed and cylinder removed rather than rip out the cable the use was changed. With combi-boilers there must be many other houses with the same?

Your second question concerns zones where cable is allowed. A cable concealed in a wall or partition at a depth of less than 50 mm from a surface of the wall or partition shall be installed in a zone within 150 mm from the top of the wall or partition or within 150 mm of an angle formed by two adjoining walls or partitions. Where the cable is connected to a point, accessory or switchgear on any surface of the wall or partition, the cable may be installed in a zone either horizontally or vertically, to the point, accessory or switchgear. See regulation 522.6.6 and the main word is “or” not “and” so either up/down or side to side not both. Also the same regulation refer to protection either with special cable or an RCD so if the supply is not already RCD protected there could be a problem.

Since a Kitchen is a special location, and any work needs either to be registered with local council building control or be completed by a registered electrician under Part P. It will therefore of course need to be right.
Eric
ericmark

Postby flandros » Sun Oct 05, 2008 1:28 pm

Thanks Eric, l
looks like I'll be getting someone in then as kitchen is a special location.
cheers.
flandros
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