plan of work

[the pict]

Hi all I would welcome opninions on the planned changes below, this is my own property,
Last year we built an extension as a self contained self catering holiday let, cooker & hood, shower, kitchen ring, toilet and kitchen lighting,
I have a long tails run and the chaps from hydro fitted an isolator (1) between meter out and CU, I intend fitting a fused isolator (2) upstream from this isolator (1) now there is mention of the 3 metres limit for tails I take it thats where I need the isolator (2) I also need to supply the CU in the extension, now I intend to take that from henly's just before my main house CU in 16mm and via a 60A service fuse or maybe I will omit the henly,s and use the service fuse as there will be enough terminations
thoughts anyone

Pict

 

[UNG]

I think a diagram of what your proposing with some dimensions might help as I'm not sure where you are intending to locate the fused isolator on the long tails

 

[the pict]

Cheers fused isolator will be three metres from DNO cut out in 25mm 16mm E, in a cellar, from there up a void for 2 metre, along the loft for 2 metre and down a wall into a 60A service fuse tailed into the CU on the incoming end , from the service fuse live out terminals in 16mm 10mm E to the sub CU for the annexe, the bit I am unsure of is it it in the regs (I cant see it) about a fused switch at the three metre point, the rest is just to give a over view
Pict

 

[Richard Burns]

The DNO can specify (and should agree) where they want protection for cables, but BS7671 states that OPD's can be installed up to 3m from the change point 433.2.2 if it is protected and 433.3.1 (iii) and 434.3 (iv) allow the omission of protection from origin up to the CU if the DNO agrees.

Therefore the general rule is to provide a fuse to protect tails within 3m of the service head.

Make sure you have adequate discrimination with all these fuses, can't quite visualize the arrangement in my head.

 

[UNG]

I think I would the mount the fused isolator adjacent to the DNO cut out and then take the tails straight into the new CU. I don't see any need for the service fuse adjacent to the new CU also I would check if 16mm T&E will carry the load required and use this instead of tails between the fused isolator and new CU. As said previously with the fusing you suggest there could be issues with discrimination which is why I would omit the service fuse adjacent the new CU as it is not necessary in my opinion

 

[Richard Burns]

omit the service fuse adjacent the new CU as it is not necessary in my opinion

You could put an isolator there just for convenience in isolating the CU.

 

[UNG]

You could put an isolator there just for convenience in isolating the CU.

You could always use the CU's built in isolator to isolate it. Why put in unnecessary equipment it costs money for no useful purpose