I am looking at the possible solutions for overcoming high Zs on a single ring covering an entire bungalow.
It's on a TNS with Ze of 0.65 ohms; Z@db L-N 0.24 ohms
r1 0.80, rn 0.81, r2 1.13
(R1+R2) 1.34 as there are some spurs; I was getting about 0.6 for sockets on the ring compared to expected 0.49.
0.6+ 0.65 gives me 1.25 against max measured of 1.1 so the sockets on the ring are close but not complying with regs once I install a modern CU, the spurs will still be a long way out. The property was built in in the 1960's and by the look of it rewired in the 1980's; most of the wiring looks in reasonable condition but the CU is probably the original at the moment with rewirable fuses.
My current plan is to split the ring, with one 32A ring for the kitchen; short cable runs should bring me well inside required limits for a 32A breaker.
Then the ring covering the rest of the house could be on a 16A breaker giving me a limit of 2.2 ohms, which will still cause a failure on some spurs which I will have to address. I didn't have time to check but there is a good chance the offending spurs are feed from a 13A plug top which gives more leeway on Zs but I will probably install properly or remove them.
Just wondering if it would also make sense and what the likely response would be if I ask the DNO or supplier to convert the supply to TNC-S, presumably bringing my Ze down to about 0.24 ohms. I assume they can do this by modifying connections at the supply head, they need to visit anyway to install an isolator and move the meter a bit to make room for a new consumer unit.
Is there a down side to converting from TNS to TNCS?
Does my plan make sense?
Thanks
