by ericmark »
Tue Aug 11, 2015 11:20 am
The main point when working on a ring final is the testing mainly to ensure it stays being a ring. Unless you can test then it's really a non starter.
Assuming you can test the ring has two cables rated around 22 amp feeding every socket, but any spur off the ring has only one cable so with a 32 amp MCB it could be overloaded unless we put something to stop it.
So once we spur we need to go to a 13A fuse be it in the socket or in a fused connection unit (FCU) it does not matter so the unfused cable must feed only one device and in theroy the cable should not be longer than 3 meters. I don't know why but a double socket is allowed even though it could have 26A load but that's only exception everything else needs to be limited to 13A by a fuse.
To extend the ring I will normally fit a device each end of the extension be it a FCU or a socket. You can get grid sockets where you have two individual sockets in the size of a normal double socket very handy to extend with.
Before I extend a ring I use a loop impedance meter to see the value and work out if adding more sockets will exceed the permitted volt drop or ELI although now since all sockets must be protected by a RCD the ELI is not really an issue.
One problem in older systems is although old cable and sockets do not need up-grading any new socket or buried cable less than 50 mm must be RCD protected and older fuse boxes and consumer units will not take RCD's. So often it's either a consumer unit change or the use of RCD FCU to spurs.
The regulation changes some times means even just moving a cable means a consumer unit change because of need for RCD protection.
Not enough info to give a full answer but I hope it gives you some pointers.
