Why would it be? The 2.5 might be for where the cable is passing through thermal insulation or high ambient etc. It could just be for volt drop, have installed 25mm² tails onto a 70mm² cable for VD before.Some of the things are hard to notice-sliced grommet could be difficult to pick up-on the last test they had 1.5mm wire feeding 2.5mm wire but that wasn't a fault?
Depends on what the load is really.also are the mcb's supposed to be type B? cheers
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