ring main extention

[david parnell]

I want to extend my downstairs ring main into my new conservetory.
I am a qualified electrician with City & Guilds Certs but I have been in a different trade for many years now and i am not up to speed with the latest regs. I now the basic principles of connecting to the back of existing sockets but I can not find wether there is a limit to how long a ring main can extend to. I will also need to bury the cables in the concrete floor I intend to use plastic conduit between connections is there a depth recomendation?

 

[Adam_151]

The length of a cable in a ring final circuit (as is the cable in any other circuit) is limited by the constrainsts of volt drop and earth fault loop impedance, the on-site guide to BS7671:2001:2004 has the max length down as 88mm if memory serves, the maximum area allowed to be served is 100m² (this is based on diversity considerations based on the number of portable heaters likely to be used), kitchens and other high loading areas may need more assement of the likely loading, also care should be taken to ensure that high loads are not grouped towards one end of the ring final circuit (as might be the case if you used a single rfc for a ground floor, and the kitchen was on one end of it)

Cables buried in the ground should be surrounded by earthed metal suitable for use as a circuit protective conductor and at sufficent depth to be clear of any reasonably forseeable disturbance of the ground

(so plastic conduit is out... but you may bury galv in the screed, as you wouldn't be digging in the conservatory floor as you would in a flower border... )

Some types of electrical work are notifiable to your local BCO, but adding points to an existing circuit in a location thats not a kitchen, special location/installation (includes bathrooms, pools, etc... rest of chapter 6), or outdoor installation is non-notifiable. However if you were to install a new circuit then that would be notifiable

 

[lizbug]

The only thing that is regulated about ring mains, are the cables sizes, that is 2.5mmsquared cable for your standard ring mains, protected by a 30 or 32 amp breaker. You are allowed an unlimited amount of sockets on a ring, so long as the total floor area for your ring main does not exceed 100 square metres.

YOu will not have to inform building control, but it will have to be inspected and tested under the new building regs, and an electrical installation certificate completed for it.