16mm or 25mm tails

[ac1951]

Just had an Isolator fitted by Eon and I told the guy I would be increasing the tails from the new isolator to the CU from 16mm to

25mm. His response was, I wouldn't bother your mains fuse is only 80A so 16mm is enough and anyway the tails from the meter to the isolator on only 16mm.

I thought the recommendation was to use 25mm minimum when changing a CU. Comments please ?

Andy

[jgharston]

Supplier's requirements are 25mm from supply head to meter [OSG 2.2]. From there onwards regs requires the cables to be the size required for the rated current capacity of the installation [OSG Table 6D1, IEE Table 4D1A]. If the CU is "at a distance", the cables must be the next size up.

So, if the installation is rated at 80A, then 16mm cable complies. There's a bit of hand-waving in the regs that makes it ok that the "undersized" cable is protected at the consumption end instead of at the supply end.

-- JGH