ring or radial


Postby winston » Mon Dec 31, 2007 2:11 pm

How do i tell the difference between a ring main circuit and a radial circuit
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Postby stevenc1603 » Mon Dec 31, 2007 4:47 pm

If you can look at the wiring inside the consumer unit that is connected to the relevant fuse or MCB. Remember to work safely, power off before you take the lid off. If there is only 1 wire connected to the fuse/mcb then its a radial, if theres 2 then its a ring.

Also a ring should be fused to 30a and a radial at 20a (32 and 20 for mcb)
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Postby ericmark » Mon Dec 31, 2007 5:29 pm

This requires a test. An electrician would disconnect the wires in the consumer unit and test continuity between the two cables on the live and return terminals. I am sure this is not want you wanted. The problem is many circuits that should be rings are in fact spurs due to the ring being broken some time in the past.
All sockets on a ring main have at least two sets of wires connected to them.
But spurs may also have two sets of wires.
Rings are normally feed with 30 or 32 amp fuse or MCB.
But if feed in 4mm then spurs could also be feed with 30 or 32 amp fuse or MCB. and if it was originally a ring but due to fault is now a spur then it could be feed with 2.5mm and 32 amp.
So although if connected to two cables or 2.5mm and supplied by a 32 amp fuse or MCB it should be part of a ring there is no guarantee which is why there is a move to doing away with ring mains.
Only UK has ring mains which are only possible because of our fused plug tops. Since we want to harmonise with the rest of EU it makes sense to do away with ring mains.
We have long realised the problems with ring mains and have recommended all houses are tested every 10 years or on change of occupants or use.
I have in the past put two block connectors on the two cables feeding a socket and tested both blocks with both earth loop and PSC to ensure it is part of a ring main before adding a spur. Using a standard multimeter will not check for bad connections but can check for ring main.
But in the main people asking questions on this don't have access to meters or the knowledge or expertise to do these sort of tests.
Since all electrical repairs or alterations should be tested once complete and the reading recorded irrespective of if they come under part P no DIY person should really do any electrical repairs but we know they will so try to help them do it in as safe of a manor as we can.
You must reflect on your skill and decide if you have enough to proceed? We as electricians tend to assume if you don't know what PSC Prospective Short Circuit Current is then you should not be working on electrical circuits. I think that is fair?
When teachers in schools are corrected by pupils because of their lack of knowledge of electrical systems we will always have problems to quote. "People who think they know it all are especially annoying to those of us that do."

All best Eric and a happy new year.
ericmark


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