Bonding

[ratboymark]

hello
just thinking of doing a job witch would involve 6mm twin and earth running in the loft to a galvanised knock out box and join it to 6mm SWA witch will feed a 2 way board in a shed should i run some 6mm earth to the box so that there isant a reduction in cable size also what reg would this relate to
any advice or thoughts much appreciated

 

[Deleted member 26818]

No, just ensure the box is earthed to the T&E CPC, and that the armour is also connected to the T&E CPC.

 

[somersetsparks]

Well in theory, you have a large enough earth in the twin and earth not to need a 6mm run seperately, you can work this out by doing an adiabtic equation. However it wouldn't hurt to run a 6mm if you feel like it!

 

[ratboymark]

i think i maby will run a extra earth just be sure then, all test redings would be ok using the t & e earth but, i think theres a possibly a reg some where which would mean the armature of the swa would need to have equepotenial bonding

 

[yellowvanman]

Well if you've got TNC-S then the 6mm earth is still not enough for bonding!

The fact that a manufacturer has made a 6mm T&E with a 2.5mm CPC would show you that the 2.5 is big enough. As has been said already use the adiabatic equation to confirm.

If your unsure, post the following info and I'll calculate it for you:

Overcurrent device type and rating

 

[ratboymark]

it is a tnc-s with a type b 32amp i work it out to be 1.5 mm min required but would that be ok to bond the armature of the swa

 

[Deleted member 26818]

Minimum size bonding conductors on TN-C-S is 10mm².

 

[yellowvanman]

You 'earth' the armour because its an exposed conductive part, bonding is a connection to an extraneous conductive part!

 

[ratboymark]

yes that make total sense ive gotten mixed up with the terms thanks 4 the help