Dad has a kiln in a workshop at the bottom of his garden, rated at
11.25kW, so maximum current 49A assuming 230V (perhaps notionally 47A given its age, the rating plate mentions 240V/415V rather than 230V/400V, it can be wired for 1ph or 3ph, he runs it on 1ph).The main part of the run from the house is 35m of 16mm^2 SWA, so expected to give a voltage drop around 5V.
He's keen to reduce the voltage drop (thinks this will reduce the duty cycle, I suppose it will, but I have my doubts if it will be a significant effect).
I know it is normally frowned on to parallel-up conductors to give increased current carrying capacity ...
But given that the SWA that is installed actually is four core, would it still be bad practice to parallel the live and neutral cores *just* to achieve equivalent of 32mm^2 thereby reducing voltage drop? To clarify, the MCB(s) would not be uprated, just done to halve the current in each core, if somehow one core were to go open-ciruit, the current in the remaining core would end up the same as it presently is.
I can envisage that physically getting 32mm^2 of strands securely into the henley blocks at the house end and the terminals of the consumer unit in the workshop might be a challenge.
This would also involve switching the CPC from one of the cores to the steel armour. MCB trip time calculations certainly aren't in my day job, given this is not handheld equipment and is effectively a submain, does a 5s disconnect time apply, rather than 0.4s?
I can see that 35m of 16mm^2 gives R1 as 0.403 ohm for single core (or 0.202 ohm for double cores) R2 as 1.085 ohm PME supply assumed Ze 0.35 ohm
Assume worst case where one core has failed prospective fault current = 230V / (0.35 + 0.403 + 1.085) = 125A
For a 50A type C MCB, a quick glance at the curves, I think this gives a disconnect time of approximately 70 seconds, oh dear, I suppose that alone is enough to rule out the changes he has in mind !!!
Seeing that, I went on to check the existing situation which uses one
16mm^2 core each for live, neutral and CPC fault current = 230V / (0.35 + 0.403 + 0.403) = 198A from the 50A type C curve this still gives a disconnect time of 20s !So even the existing CPC doesn't meet the disconnect time for a 50A type C MCB, even getting an actual measurement of Ze rather than assuming
0.35 ohms, couldn't possibly result in a low enough Zs to allow a type C MCB.But reverting to type B would meet the disconnect time (I think he only recently changed to type C at the house end because of poor fault discrimination).
OK, so I think the disconnect time issue has trumped the original question about using parallel conductors, any thoughts (or mistakes in my calculations)?