Earthing old coduit.

[biggaf]

Doing a rewire at the moment on a house that has old conduit down the walls to each socket/light switch, and need to replace the back boxes. Are there any clamps you can use to earth the conduit? If not,it could turn into a bit of a nightmare? Anybody got any tips? I don't want to rip the conduit out as it will wreck all the deco.

 

[davie spark]

If the conduit is continuous use 'slip' couplings which come with an earth terminal and run a single CPC into the switch/socket box or use threaeded coulpings that come with an earth terminal for that very purpose and again connect the CPC into the box. If it's only conduit drops, you could if you're worried still do what I've suggested. Note that any protective capping over pvc/pvc needs to be earthed/bonded into the accessory box so conduit drops probably need earthing/bonding also. :yes:

 

[davie spark]

Sorry, also meant to add that if the conduit is continuous but old you should probably install a CPC inside it anyway, for all circuits.

 

[telectrix]

This will take you back Colin ....................:teeth_smile: as you say mate Earth wot Earth

i prefer the brass ones myself. a squirt of WD40 evey couple of years, they'll last us lot out.

 

[DPG]

'Note that any protective capping over pvc/pvc needs to be earthed/bonded into the accessory box '

Surely metal protective capping does not need to be earthed? What if it is joined - do we link the lengths together? Daz

 

[davie spark]

Yep, you have to bond it to the accessory box, the capping works not by stopping nails going through it because they DO go through it, you can 'nail' it to the wall. When it's bonded and someone puts a nail through it into a phase cable only the fault current will hit the capping and due to the fact the capping is bonded the fault current will then flow to earth enabling the MCB/RCBO to trip or fuse to blow.

 

[DPG]

What bonding clamps do I use to bond it? Daz

 

[benji]

never bonded capping in my life ,if you had to everybody would use plastic capping

 

[Deleted member 26818]

Yep, you have to bond it to the accessory box, the capping works not by stopping nails going through it because they DO go through it, you can 'nail' it to the wall. When it's bonded and someone puts a nail through it into a phase cable only the fault current will hit the capping and due to the fact the capping is bonded the fault current will then flow to earth enabling the MCB/RCBO to trip or fuse to blow.

This is not an acceptable method of providing additional protection.

 

[davie spark]

Without taking the time to look into the regs, if capping is not an acceptable method of additional protection why is the stuff produced specifically for that purpose?

 

[davie spark]

Plastic capping would not let you incorporate ADS installation if a nail was put through it, you've missed the pont of my post.
Any housing work I've done in the past that is paid for with government money involved capping where there was no conduit installed and it had to be metal and it had to be bonded to afford ADS in the installation. Because it can nailed through. It can be cut to size with tin snips as you will know, so nails will go through and die to that fact it required bonding, it had to drilled and a bonding conductor crimped and fixed using either a self tapping screw or small brass nut and bolt.
Remember compliance with B.S.7671 is 'minimal' compliance, you can if you wish and lots of consultants/designers will have their specification 'above' minimal complaince. So, in summary, to install metal capping without bonding it is pointless.

 

[Deleted member 26818]

It's not.
It's designed to protect cables from other trades during construction.

 

[malcolmsanford]

Where Spin is coming from I think is that even if you do earth the metal capping you will still have to afford additional protection to the cables if it is buried less than 50mm, or the cable itself has an earthed covering.

Only earthed conduit to BS 61386 or earthed trunking/ducting to BS 50085 will comply to allow the omission of additional protection by RCD.

 

[Deleted member 26818]

The thing is, sheathed cables, conduit and trunking all have British Standards which they must meet.
One of the conditions of those Standards is that they provide sufficient continuity for ADS.
Obviously the continuity of conduit and trunking is dependant upon the Manufacturer's instructions being adhered to.
In the case of metal capping, it may well have a British Standard, but I doubt very much that there is a condition in that Standard for it to provide sufficient continuity for ADS. Especially as to provide that continuity relies on the selection and connection of earthing conductors which are outside of the manufacturers control.
It is a requirement when using a method, or equipment that does not meet the requirements of BS7671, for the designer to note the departure on any certification, and to confirm that the departure will offer the same degree of safety as would be achieved by compliance with the Regulations.

 

[davie spark]

I don't think I'm making my point here in previous posts by the looks of things. The original question asked was about earthing metal conduit and the replies came thick and fast re conduit drops and continuous conduit installations. Then someone (before me) mentioned 'metal capping'. Now my point is/was (even though I know it's not a recognised means of CPC) BUT! if it's going to be used, what is the point of NOT earthing it, it will conduct fault current and that will assist in the function of ADS whereas if it is not bonded/earthed there is the scenario where a nail or screw which has penetrated the capping and is touching only a live conductor will remail live and if that nail or screw is supporting a conductive item, then that will also be live and exposed to touch as will the nail or screw. Earthed/bonded capping has to be safer than non earthed/bonded capping. Personally however if I had a choice, I would use non conductive capping if I had to install capping at all. On a 'side note' I have in the past been involved in installations where metal capping has been asked for and in 'all' specifications it was to be bonded. I also know inspectors who probe finished plastered walls to continuity test the capping to confirm it has been bonded and earthed. BTW B.S.7671 does not mention capping, even in 522.

 

[DPG]

Do some inspectors really probe through newly plastered walls to test for capping bonding? Daz