ring main wiring


Postby Muzzy » Thu Nov 18, 2010 7:53 pm

Had a new consumer unit fitted at the start of this year and just found out the upstairs 13amp sockets are connected to the same trip as the downstairs 13amp sockets. Only found this out when i wanted to change a upstairs single socket to a double one. My question is:

1 Is this ok as is.

2 How easy is it to change so they are on there own circuit.

Tried contacting the spark who fitted unit, but no response.
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Postby ericmark » Fri Nov 19, 2010 4:01 pm

314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.

That is how it is worded in regulations. Many houses have just one ring main and when the whole supply is 60A having just 32A for ring mains is unlikely to cause a problem. Remember any fixed appliance over 2Kw should have it's own dedicated supply.

The problem is:- 314.1 Every installation shall be divided into circuits, as necessary, to:
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.

So since now we need an RCD on all non dedicated sockets under 20A it is likely that where multi IT appliances are used each with an EMC filter that the total leakage can exceed 15ma the safe limit of a 30ma RCD.

But nothing says you must have two ring mains so unless it is tripping out then very little you can do. Do remember it says "normal operation" so faulty equipment tripping out the RCD does not count so in real terms it must trip out once a month at least before you can really complain and even then it would be hard to prove it's not due to faulty equipment.
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Postby Muzzy » Fri Nov 19, 2010 7:14 pm

Thanks for your reply Ericmark.

You mentioned ring main tripping out, this was happening after the unit was changed over but after about two weeks it settled down, until the other day when I switched the wall light on in the conservatory, it tripped the ring main for the sockets. This light is a single cable fed from the back of a socket through a switched spur.

Can I just add, we had no problem with the electrics when connected to the old wirelex fuse panel, both socket ring mains had there own fuse, up and down. Is it possible the electrician when fitting the new consumer unit has managed to get the cables mixed up for the ring mains and instead of ringing them out, he just pushed them all into the same trip.
Muzzy
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Joined: Thu Nov 18, 2010 7:39 pm


Postby ericmark » Sat Nov 20, 2010 6:03 pm

It is unlikely that if the system was working and is not know it is due to a mistake when the consumer unit was changed.

However mistakes can easy be made and in the past I have found where two 32A MCB's were controlling the same group of sockets and this could of course allow a massive overload should a second fault accrue then there could be burnt out wires.

However much one tries to work out things on a forum one only has a general feel and we can get things wrong.

If I was in same position then I would consider it worth while to get an independent assessment and a PIR completed. I hope nothing wrong of course but if your not sure then you have to consider what piece of mind is worth?

Most DIY people haven't got the equipment to test so it is really down to employing an electrician to inspect and test.
ericmark
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Postby Muzzy » Mon Nov 22, 2010 5:54 pm

Thanks ericmark, will take everything on board. :wink:
Muzzy
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Joined: Thu Nov 18, 2010 7:39 pm


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