Hi Folks, have just finished replacing an old fuseboard with a new rcbo jobby. To say there have been a few surprises would be putting it mildly. The property is a late 60's bungalow and has had all the usual mods. Loft conversion, new kitchen etc. First surprise was the 3, 32A fuses with 8 conductors, variously paired, turned out not to be 3 rings with a couple of spurs but 1 ring and 6 completely independent radials. Oh well, easy enough to change a couple of rcbos and derate for the individual circuits. However...
Next up the lighting, 3 circuits, apparently to 2 separate 6A fuses, now 3 rcbos, yep you guessed, the dreaded shared neutral and pop, the kitchen light trips the hall light and all manner of dumness. Identify the 2 connected circuits and put them both on the same breaker, all good then? Sadly not. One of the lighting circuits, the one not interconnected by shared neutral, tests through fine, readings at all points, normal. The "twinned circuits", now on the same breaker are a different matter though. No tripping and the rcbo test button working as ought, however I can't get Ze and I can't measure R1+R2 as there is 22V running to earth with a proportionate decline in L to N voltage.
If I try to do a 3 point no trip Zs the meter says I have reverse polarity, swap the leads and I get exactly the same. I've pulled down the ceiling roses on the affected lights and can't see any loose or ballsed up connections but I have spotted the dreaded single wires of doom and that a couple of the lights have no cpc. Those that do I can't check to earth continuity as the voltage is too high. So good people where next? Split the circuits down and IR test? Is there anything less destructive to try first?
Suggestions very welcome!
Next up the lighting, 3 circuits, apparently to 2 separate 6A fuses, now 3 rcbos, yep you guessed, the dreaded shared neutral and pop, the kitchen light trips the hall light and all manner of dumness. Identify the 2 connected circuits and put them both on the same breaker, all good then? Sadly not. One of the lighting circuits, the one not interconnected by shared neutral, tests through fine, readings at all points, normal. The "twinned circuits", now on the same breaker are a different matter though. No tripping and the rcbo test button working as ought, however I can't get Ze and I can't measure R1+R2 as there is 22V running to earth with a proportionate decline in L to N voltage.
If I try to do a 3 point no trip Zs the meter says I have reverse polarity, swap the leads and I get exactly the same. I've pulled down the ceiling roses on the affected lights and can't see any loose or ballsed up connections but I have spotted the dreaded single wires of doom and that a couple of the lights have no cpc. Those that do I can't check to earth continuity as the voltage is too high. So good people where next? Split the circuits down and IR test? Is there anything less destructive to try first?
Suggestions very welcome!