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.

 

[malcolmsanford]

I use to know a lad that would slip a jubilee clip along the conduit, strip back a piece of 1.5mm Green (then) and as he tightened the clip he slid the bare conductor inside it to "trap" it. Always got a good earth .......................

To be honest surely it's more work earthing the conduit at each point, and then binding them all back at the CU, and chances are that the drops are not continuous back to the CU unless it's a totally installed system utilizing bushes and couplings.

I'm taking it that this is the old VIR system and using the "unthreaded" type conduit. IMO I would wire in T+E just using the drops as mechanical protection and access to back boxes

 

[biggaf]

Hi Malcolm,
Cheers for the quick reply! I'm just unsure about the fact of it needing earthed or not. Can you just use it as mechanical protection and leave it unearthed? This would save alot of time. And energy!

 

[hillbillie]

Whether its through conduit, trunking, the armour of swa or a dedicated cpc, you need to have a continuous earth path from the d/b.

So, after following the respected members advice on connecting new back boxes to old conduit, test at each back box/fly lead to see if you have continuity.

 

[telectrix]

if it's just the drops that are in conduit, and there is no continuity back to CU, then i suggest not bothering to earth it, but ensure all circuits are protected by a 30mA RCD.

 

[malcolmsanford]

The drops in theory will be classed as exposed conductive parts and should be earthed as it metalwork that forms part of the installation that could become live when basic insulation fails.

 

[biggaf]

The installation is just conduit drops, wired in T+E back to an RCD, so I think earthing the back boxes as you've all said will be the best option.
It was just something I was unsure about, but cheers guys for the quick replies.

Thanks again,
biggaf.

p.s. there may be more questions as the installation progresses, who knows!

 

[telectrix]

The drops in theory will be classed as exposed conductive parts and should be earthed as it metalwork that forms part of the installation that could become live when basic insulation fails.

agree, but a lot of installs were done pre 16th with just the drops in black enamel tube.no earthing. likewise, do we class metal capping as exposed conductive part, and earth that? assuming we protect the cables with RCD?

 

[Deleted member 26818]

The drops in theory will be classed as exposed conductive parts and should be earthed as it metalwork that forms part of the installation that could become live when basic insulation fails.

Not too sure about that Malcolm.
I would have thought only accessible exposed conductive-parts require earthing.

 

[malcolmsanford]

I agree spin that the buried part in the wall would in un-accessible but if you had as in the old enamel conduit parts exiting into a void or loft then as said in theory they are accessible.

I agree with Tel in all honesty with RCD protection there is little chance of these becoming live and someone actually in the loft touching them, and getting a shock, but in theory and in those circumstances I guess they are.

 

[telectrix]

having said that, i have come across several cases where the tube has projected into the attic, then mr. diy has boarded the attic, crushing the cable onto the tube. piercing the insulation. in most cases, the tube has shorted out the L & cpc, thus operating the OCPD or , where fitted, RCD. nice bit of fault finding in these cases.

 

[oldtimer]

I asked this on another forum (Voltmum) because i was quoting for a CU change and the property was a downstairs villa flat withe the lights wired in continuous conduit plus the junction boxes were in the upstairs flat but circuit had been rewired from old VIR to 1.5 mm pvc and Select replied to my enquiry stating if you got the correct Zs readings usung the conduit as an earth then this was acceptable I asked this question as I was trained in the 14th edition where you did not run a seperate earth as long as the installation was "Electrically and Mechanically sound"

 

[Engineer54]

I agree spin that the buried part in the wall would in un-accessible but if you had as in the old enamel conduit parts exiting into a void or loft then as said in theory they are accessible.

I agree with Tel in all honesty with RCD protection there is little chance of these becoming live and someone actually in the loft touching them, and getting a shock, but in theory and in those circumstances I guess they are.

Those conduit drops were originally earthed, ...via the T&E CPC, being taken to the back box earthing point. ...Well at least on the socket outlet points anyway. ...No CPC in the old lighting Twin stuff ...lol!!!

 

[malcolmsanford]

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

 

[topquark]

Those bakelite accessories were a little more robust than some of todays plastics as well

 

[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

 

[davie spark]

Yes, I'm only talking about a hole made by a probe similar to the point on a dart.
Here's another thought on the subject of capping, if it was heavy duty i.e. 3mm thick, it would be considered by B.S. 7671 sufficient to prevent nails etc going through it, (in the same way conduit is considered), I think to solve this debate people should either fit heavy duty (if it's thick enough and clients/consultants/designers want it earthed/bonded), or don't fit any.