Addition to old installation - routing through trunking to supply a sub-board with two 6mm SY cables.
However, I can't find any info on sizing of MCB to maximum Zs for parallel cables - -?
Seems to me the problem could be using calculated Zs for the two in parallel as in the event of a fault occurring at far end in one cable only - you're only dealing with the Zs of that cable to meet the MCBs overcurrent requirements - - (i.e. this would be double the Zs of the two in parallel)
So it's ok doubling current carrying capactiy for the two in parallel, but it seems using parallel Zs to determine suitable MCB could be bad practic here. In which case I'm goosed!
Can anyone shine a light ?
However, I can't find any info on sizing of MCB to maximum Zs for parallel cables - -?
Seems to me the problem could be using calculated Zs for the two in parallel as in the event of a fault occurring at far end in one cable only - you're only dealing with the Zs of that cable to meet the MCBs overcurrent requirements - - (i.e. this would be double the Zs of the two in parallel)
So it's ok doubling current carrying capactiy for the two in parallel, but it seems using parallel Zs to determine suitable MCB could be bad practic here. In which case I'm goosed!
Can anyone shine a light ?
