cant find what im looking for!

[Danny Gray]

Ihave a job to move a cu. The plan/easiest option is to extend the tails already in henly blocks up into the attic (its a bungalow) across and back down. Works out to be 7m run. can anyone point me in the right direction in the big yellow book where i can find the relevant information on max length and methods of protection.
thanks in advance.
Danny

 

[SparkyChick]

Recommended max length is 3m. It's not in BS 7671 as it's specified by the DNO. I think that's the generally accepted limit, but you could always have a conversation with the DNO for the area and get their view on it.

A suitably rated switch fuse at the origin should suffice (100A switch fuse with an appropriate fuse), and of course suitably rated tails.

 

[Octopus]

FWIW I don't recall it being in the byb.... But network service providers have a distinct view....

 

[SparkyChick]

Although a better solution instead of tails might be a run of appropriately sized SWA from the switch fuse, depending of course on the installation methods.

 

[LankyWill]

Just put a kmf upfront or use swa for your mains, id opt for the kmf as it's a quicker job.

 

[Ian1981]

Ihave a job to move a cu. The plan/easiest option is to extend the tails already in henly blocks up into the attic (its a bungalow) across and back down. Works out to be 7m run. can anyone point me in the right direction in the big yellow book where i can find the relevant information on max length and methods of protection.
thanks in advance.
Danny

If you do use tails I would make sure that they are in some kind of containment including in the loft.

 

[Danny Gray]

I was trying to stay away from 25mm swa but yes all in box trunking. I'll probably kick myself when u tell me but what a kmf?

 

[Ian1981]

I was trying to stay away from 25mm swa but yes all in box trunking. I'll probably kick myself when u tell me but what a kmf?

This is a wylex switch fuse for protecting tails over 3 meters

 

[Danny Gray]

I was under the impresion (what i was trying to find in the book) it would need to be rcd protected if ran in tales rather then swa?

 

[Ian1981]

I was under the impresion (what i was trying to find in the book) it would need to be rcd protected if ran in tales rather then swa?

You don't want to rcd the tails as if the rcd trips you'll lose all the power to the house.
As long as you don't chisel them into the wall your fine.
TT is a different story tho

 

[davesparks]

I was trying to stay away from 25mm swa but yes all in box trunking. I'll probably kick myself when u tell me but what a kmf?

So stay away from 25mm SWA then, use a different size. It must be one hell of a big bungalow to need a submain that big!

 

[Ian1981]

Agree with Dave 16mm swa on a 80 amp switch fuse should be ample depending on your maximum demand .
Swa should have the armour bonded to earth and if possible can be buried in the wall.

 

[Danny Gray]

You don't want to rcd the tails as if the rcd trips you'll lose all the power to the house.
As long as you don't chisel them into the wall your fine.
TT is a different story tho

no its tncs

So stay away from 25mm SWA then, use a different size. It must be one hell of a big bungalow to need a submain that big!

Who mentioned sub main? Its the main board woth a total load of 70 amps

 

[Ian1981]

no its tncs

Who mentioned sub main? Its the main board woth a total load of 70 amps

If your extending the tails and going into a switch fuse ( don't know if you are or not) then the extended tails/swa via the switch fuse would now become a sub main to your consumer unit

 

[Danny Gray]

If your extending the tails and going into a switch fuse ( don't know if you are or not) then the extended tails/swa via the switch fuse would now become a sub main to your consumer unit

Point taken. I'll just crawl back into my hole!

 

[Ian1981]

Point taken. I'll just crawl back into my hole!

Haha don't worry about it, that's what's good about the forums you pick stuff up.

 

[Danny Gray]

I was just thinking the same. I do love this site. Any questions or advice there's always someone who knows or can point you in the right direction. Cheers guys