As far as sockets are concerned what’s the best method to use?
Although permitted by regulation 433.1.204 BS7671 the usual 2.5mm ring has become somewhat of a tradition, but maybe it has outlasted it’s use. Being involved in domestic periodic Inspection and Testing over the years I have noticed an alarmingly large number of so called rings that are just not. Giving rise to the possibility of overload and potentially fires from a 2.5mm cable being protected by 30 or 32 Amp device.
From a testing point of view it’s much easier to test a radial socket circuit; continuity of cpc (R1+R2), insulation resistance and polarity etc than it is to test a ring socket circuit; continuity of ring final circuit conductors (r1, rn and r2) to confirm polarity by cross connecting ‘there’s a good explanation of this in the On-Site Guide’, insulation resistance etc.
Also, in my opinion much easier to wire a radial circuit, either 20 Amp 2.5mm or a 30 / 32 Amp 4.0mm just start at you disboard and finish at the last point. No going back round, up, down or through like you do with a ring.
Similar restriction apply to both the ring and radial with regard to unfused and fused spurs. Have a look at Appendix 15 BS7671:2008+A3:2015 there are even pictures.
So after years of installation and inspection and testing I think I’ll have to come down on the side of the radial circuit for sockets, and I’m guessing that in the years to come (18th Edition) we will see the dropping of the 32 Amp 2.5mm ring main.
One more thing, don’t forget regulation 411.3.3 Additional protection and slap a 30mA RCD on as well.
Cheers
Paul Moseley (Electrician/Tutor)