N
NickD
Wouldn't mind the views on some wiser heads than mine on the following - my experience with TT is limited. It's some testing I did for a friend that I doubt I would have taken on for actual income.
1. Leakage breaker: Installation is TT (but see below). It has an old-school Bakelite-looking Crabtree earth leakage breaker between the meter and the CU, black with yellow test button at bottom (can't remember how exactly it was labelled but there were no identifying details, model number, trip current, delay time etc., nothing - I am aware it probably only trips on actual earth conductor leakage current rather than on residual L-N imbalance). CU is old-school BS3036 job. I could not persuade the breaker to trip with any actual RCD test (S range or G range) up to and including 1000mA, though at the higher currents you could hear the breaker thrumming away as if on the point of tripping out. However, when I subsequently did a Zs test at a socket, not on the RCD-safe setting, the breaker tripped anyway. Test button works. What do you make of this?
2. Earthing: I cannot confirm the presence of an acceptable 'by-design' means of earthing. I cannot find any earth rod. There is no MET outside the CU; at the CU earth bar there were two possible candidates (solid green, 6mm) for the earth conductor. The first however appears to be the MPBC for the oil supply (Zs measurement on it is 400ohm, and it shows <0.1ohm continuity between conductor and oil pipe on R2 test). The other shows Zs of about 40ohm, and goes into the earth terminal on the leakage breaker then disappears into the wall, so *could* be the earth conductor, however I cannot find where it goes and it could perhaps instead be bonded (inaccessibly) to the water supply somewhere (though having said that, R2 continuity between it and the pipes at the stop cock, where there is no visible earth bond, is about 300ohm). Water is from public supply network. Near the meter there are the remnants through the wall of older tails plus what was probably once a nasty old multistrand earthing conductor. Outside and below it is empty metal conduit and in the ground what could conceivably have been an earth rod, it seems to have no other obvious reason to be there...although (even when cleaned back to bare metal - looks to be steel, it's pretty old) it gives a Zs of 350 ohm. Again, what do you make of this? I'm aware the 40ohm Zs is potentially a perfectly acceptable value but I am troubled, possibly needlessly, that I can't point to it being provided by a trustworthy means of earthing. I know it could be to structural steel or similar and this would be OK, but I would feel happier about it if I'd seen a rod and could rule out the 40ohm being provided by a diguppable water pipe or similar.
Cheers for your help.
1. Leakage breaker: Installation is TT (but see below). It has an old-school Bakelite-looking Crabtree earth leakage breaker between the meter and the CU, black with yellow test button at bottom (can't remember how exactly it was labelled but there were no identifying details, model number, trip current, delay time etc., nothing - I am aware it probably only trips on actual earth conductor leakage current rather than on residual L-N imbalance). CU is old-school BS3036 job. I could not persuade the breaker to trip with any actual RCD test (S range or G range) up to and including 1000mA, though at the higher currents you could hear the breaker thrumming away as if on the point of tripping out. However, when I subsequently did a Zs test at a socket, not on the RCD-safe setting, the breaker tripped anyway. Test button works. What do you make of this?
2. Earthing: I cannot confirm the presence of an acceptable 'by-design' means of earthing. I cannot find any earth rod. There is no MET outside the CU; at the CU earth bar there were two possible candidates (solid green, 6mm) for the earth conductor. The first however appears to be the MPBC for the oil supply (Zs measurement on it is 400ohm, and it shows <0.1ohm continuity between conductor and oil pipe on R2 test). The other shows Zs of about 40ohm, and goes into the earth terminal on the leakage breaker then disappears into the wall, so *could* be the earth conductor, however I cannot find where it goes and it could perhaps instead be bonded (inaccessibly) to the water supply somewhere (though having said that, R2 continuity between it and the pipes at the stop cock, where there is no visible earth bond, is about 300ohm). Water is from public supply network. Near the meter there are the remnants through the wall of older tails plus what was probably once a nasty old multistrand earthing conductor. Outside and below it is empty metal conduit and in the ground what could conceivably have been an earth rod, it seems to have no other obvious reason to be there...although (even when cleaned back to bare metal - looks to be steel, it's pretty old) it gives a Zs of 350 ohm. Again, what do you make of this? I'm aware the 40ohm Zs is potentially a perfectly acceptable value but I am troubled, possibly needlessly, that I can't point to it being provided by a trustworthy means of earthing. I know it could be to structural steel or similar and this would be OK, but I would feel happier about it if I'd seen a rod and could rule out the 40ohm being provided by a diguppable water pipe or similar.
Cheers for your help.
