OP here - What I want to do is DIY electrics on my house extension, this will be some connecting into existing ring circuits, plus a couple of new ones. I am undertaking some basic training in a few weeks time, but I want to try and get ahead with my own project, so I want to map the exiting installation so I can see which circuits I can join into, how and where, whilst maintaining the integrity of the existing circuit. I am undertaking some training shortly, 20 days C&G - will not make me a sparks by any stretch, but will hopefully expand my DIY range and keep me safe.
Chris Gray - thanks for the tip to make it into a radial - again all too obvious once you know - I hope that is where I would have ended up anyway - but it might have taken a while.
DefyG - thanks for the alert - I never took Telectrix post to mean that R1 + R2 should deviate on a ring main, because I was certain myself that it shouldn't, but I rated it highly because it set me onto the thinking which I outline below, even though I then wrote wrongly about R1 going up as R2 went down. What I was thinking is that when step 3 testing at outlets, there are two loops of resistance from live terminal to earth terminal as per the need to divide by 4 rather than by 2. So resistance of one loop would increase as you progress from outlet to outlet whilst the other decreases, as per the increasing / decreasing proportion respectively of the 2 loops that is formed by the earth cables different cross section. So, I was trying to figure out how to disaggregate the resistance contribution of the two loops at each outlet which is overly complex compared to the simple (and no doubt correct) method suggested by Chris Gray.
So, perhaps I was too absorbed with the Stage testing, and needed to take a step back to something more obvious. However I think the Step 2 / Step 3 testing should be useful to me for identifying a spur, if there are any, rather than simply a position on the ring.
Kind regards, and thanks again to all.
Chris Gray - thanks for the tip to make it into a radial - again all too obvious once you know - I hope that is where I would have ended up anyway - but it might have taken a while.
DefyG - thanks for the alert - I never took Telectrix post to mean that R1 + R2 should deviate on a ring main, because I was certain myself that it shouldn't, but I rated it highly because it set me onto the thinking which I outline below, even though I then wrote wrongly about R1 going up as R2 went down. What I was thinking is that when step 3 testing at outlets, there are two loops of resistance from live terminal to earth terminal as per the need to divide by 4 rather than by 2. So resistance of one loop would increase as you progress from outlet to outlet whilst the other decreases, as per the increasing / decreasing proportion respectively of the 2 loops that is formed by the earth cables different cross section. So, I was trying to figure out how to disaggregate the resistance contribution of the two loops at each outlet which is overly complex compared to the simple (and no doubt correct) method suggested by Chris Gray.
So, perhaps I was too absorbed with the Stage testing, and needed to take a step back to something more obvious. However I think the Step 2 / Step 3 testing should be useful to me for identifying a spur, if there are any, rather than simply a position on the ring.
Kind regards, and thanks again to all.
