Thanks for the many helpful responses. I really appreciate it.
I’ve had to halve a ring previously to locate a break in continuity. I am famously with the concept.
I also have a plan for my testing and would welcome your constructive feedback please.
After purchasing an appropriate tester, I am ready to commence the testing. Properly! The MFT is my likely choice from what I’ve been reading above. Again, happy to pay a bit more if it provides some future proofing. Please let me know if you have any further recommendations.
1. Continuity / end-to-end tests
Whilst I thought that my earlier Fluke 2 pole tests were conclusive,
@IzzyS post shows that it’s far from it!
This will be a dead test and I am familiar with the safe isolation process.
I will locate the 6 wires for my ring. I will initially do this with the ‘good’ ring and then the ‘bad’ one. I will also ensure that everything is unplugged and the FCU is bypassed.
Here I plan to do the r1, rn and r2 tests. On the “good” ring I expect the r1 and r2 to be the same (Within 0.05) and the r2 will be 1.7 times higher due to the higher resistance of the smaller CSA. The readings for r1 and rn should be less than 1 ohm and determined by the length of cable in the ring. I don’t anticipate any issues with the “good” ring but when I do this with the “bad” ring, I think I will get a different reading for r1 and rn/r2. Even after taking into account the expected uplift for r2. The problematic reading shouldn’t be an open circuit/infinity as the fluke tester detected a closed circuit but it’s probably going to be a high reading. I think this indicates a short circuit or a loose connection?
I should now be in fault finding mode…
My plan is to split the ring into 2 radials by breaking the ring (cables disconnected and hanging mid air for the mid socket in ring) and on the CU end will have the first leg of the (now) radial in terminal block. I can then test at the break point of the ring and see if I get a high/low reading. If this leg is fine, I move on to the other and repeat the process. This should have a fault (unless I am unlucky to have multiple faults!). This is where I will need to continue halving until I’ve narrowed down where the problem is. I can then inspect the back of the socket or even try bypassing this section to see what the overall r readings look like.
I would appreciate your comments on the above as I’ve got my head wrapped around this approach if it’s the most suitable way to proceed.
2. Once the above is fixed, I am ready for the cross connection tests: R1+Rn and R1+R2
The expected results can be calculated from the above r readings.
This is where we create the figure of 8 across different wires of each leg. L from one side connected to N of the other side and the same for the other legs of the ring. This creates an infinite loop. I can then measure resistance at all and any point and it should be the same. Unless it’s a spur.
3. Repeat the above for L and CPC
I am not anticipating issues with 2 and 3 as I’ve checked the route of the ring using a wonder lead and my fluke continuity function.
My main issue is likely to be the first tests. I think…
Thanks in advance.