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