Leaving aside Part P requirements;
1)Yes,from table 4D4a/b:
cable current capacity over 63Amps so assuming massive load of 60A;
volt drop = 2.8mV/Amp/Metre, ie 2.8 X 60 X 25 =
4200mV or, div/1000 = 4.2Volts dropped, well within 4% limit ie 230 X 4% = 9.2V.
2/3) use a switch fuse (metal) such as wylex 106M, with a 60 A. fuse fitted which gives isolation & over-current protection to cable.
4)Using the above gives point to connect dble. ins. 'tails' & earth wire all at 16mm2 , these then connect with existing tails between meter & con.unit. using 'dble 'Henley Block' + earth block, which if not already fitted can be introduced into main earth wire from incoming cable. N.B. This work can only be done by qualified/registered electrician, it's the law, & supply co. will want to see test sheets to prove it!,
I have paid building control to inspect and test the whole electrical instalation. In this case would it be OK for me to do the work (and get them to check, inspect and test) or does it still have to be done by a part P electrician?
you are ok, one of the options is to pay inspection fee first then you can DIY, only thing is they won't do test readings , only look at routes, methods etc. so if you need test sheets (which are reqd. under IEE regs) say to sell property, or for insurance purposes then you would need to get that done seperately, it would have to be a 'periodic Inspection' not a 'completion Cert.' as only the person carrying out the work can issue those. Regards SPARX