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Hi everyone,
I want to repurpose an old cable that was previously used to power a 3-phase machine. The cable is 4L1.5 micc, and I don't want to replace it unless I really have to, as the cable run is convoluted/inaccessible to say the least. It was obviously installed before many other things (such as floor joists, walls etc) were built - maybe that's why they used MICC as it's all but indestructible - the builders knew it would be next to impossible to repair should it ever fail.
In any case, I want to use this cable as a feed to a small consumer unit that will power 2 immersion heaters and provide power to some control valves, via 2x16a and 1x6a B-curve RCBO. The cable is fed by a 3-pole 20amp C-curve MCB, with neutral being taken straight from the neutral bar in the DB unswitched. I'm aware this might not provide much selectivity, but if the main MCB trips, it won't be the end of the world. They're only backup heaters anyway.
After reading some other posts it would appear that I can't do this due to the fact that the neutral would be shared by all 3 final circuits.
Given that the main DB for the property only has 1 neutral that is shared by all 29 circuits (mostly single phase but some 3-phase), I'm just curious as to why my 'sub main' would be considered a borrowed neutral and the rest of the circuits in the house aren't?
I want to repurpose an old cable that was previously used to power a 3-phase machine. The cable is 4L1.5 micc, and I don't want to replace it unless I really have to, as the cable run is convoluted/inaccessible to say the least. It was obviously installed before many other things (such as floor joists, walls etc) were built - maybe that's why they used MICC as it's all but indestructible - the builders knew it would be next to impossible to repair should it ever fail.
In any case, I want to use this cable as a feed to a small consumer unit that will power 2 immersion heaters and provide power to some control valves, via 2x16a and 1x6a B-curve RCBO. The cable is fed by a 3-pole 20amp C-curve MCB, with neutral being taken straight from the neutral bar in the DB unswitched. I'm aware this might not provide much selectivity, but if the main MCB trips, it won't be the end of the world. They're only backup heaters anyway.
After reading some other posts it would appear that I can't do this due to the fact that the neutral would be shared by all 3 final circuits.
Given that the main DB for the property only has 1 neutral that is shared by all 29 circuits (mostly single phase but some 3-phase), I'm just curious as to why my 'sub main' would be considered a borrowed neutral and the rest of the circuits in the house aren't?