Bonding on tns

[m4tty]

Hi,

Can anyone let me know if/when will a 6mm main protective bonding conductor comply on a tns.

Thanks

 

[mark740]

P 134 BRB 544.1.1

main protective bonding conductor csa not less than half the csa of the earthing conductor not less then 6mm2 not more than 25mm2

May not be the complete answer but hope it helps

 

[Andy™]

providing 16mm tails with 10mm main earth

 

[Evans Electric]

As Mark740 says , the text of 544.1.1 says " and not less than 6mm" yet Table 54.8 below says " 10mm with neutrals 35mm or less" .

I did read somewhere that 6mm is OK ,as Andy says, with 16mm tails / 10mm main earth and a 60A supply fuse. This remains a grey area , anyone got an official ruling on it?

 

[Zeespark]

I would always go with the rule of thumb of at least half of the Line/Neutral size.

AndyGuinness

 

[mark740]

i may be wrong duke but i think that table is for PME supplies

i dont have the book in front of me but i think it says the rule of half the csa of the eathing conductor is not for pme and please refer to the table

again dont have the book to hand to confirm

 

[Evans Electric]

You're right Mark740, theres a comma in that middle sentence of the text that changes the whole meaning and threw me TBH. :C

So , lets get it right :-

Main Bonding cable size on a TN-S is not less than half the size of the main earth and not less than 6mm.

( Which is what Andy said, why don't I listen??)

Main bonding on a PME (TN-C-S ) is as Table 54.8

I knew all along really :Blushing

 

[tom1]

could be wrong here but it says bonding conductor shall have not less than half csa required for the earthng conductor and not less than 6mm.

say if you calculate the required earthing csa as 12mm for instance 16mm would be installed as its the closes suitable size however the bonding could still be 6mm as that is half of what is required of the earthing conductor.

does that sound about right?

 

[Nicky Tesla]

good answer.......also on a TNCS on a periodic it has been said it is acceptable if there are no signs of heat damage.

 

[wozz]

Question 12:

Alterations and additions in domestic and similar premises : Electrical Safety Council

HTH

 

[Evans Electric]

good answer.......also on a TNCS on a periodic it has been said it is acceptable if there are no signs of heat damage.

Thats what I had read.

Always gone with the half the main earth conductor size also. I've seen loads of jobs with a 6mm cut off and a new 10mm fitted so I guess a lot of guys are condemning it.