16mm sub main on a new build?

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Texdangerfield

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By a stroke of luck I've purchased what I think is an amazing new build house, complete with brand new air source heating, an independent garage with a supply and a lovely fitted kitchen complete with appliances and a shiny new induction hob. On my first walk through I'm already planning on adding an outside barrel sauna!

When checking the meter board outside I came across something that made me pause though, from the 100a isolator switch (TNS supply) which is fed from the meter (all 25mm) the sub mains into the house, which is roughly 10 metres to the consumer unit, is fed by a 16mm twin and earth.

I'll do a calculation later but surely in a newly built(2020) house this is a big no no?

 
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Does the switch incorporate circuit protection such as a fuse.

 
Why a no no?

My own house has a 16mm feed from the meter box to the CU fed from a switch fuse with an 80A fuse in it.  The max demand is only a small fraction of that.

Irrespective of size, it there is more than 3M from meter to CU there should be some form of over current protection, not just the DNO's fuse.

 
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