Earthing existing conduit

[MarkTravis]

I've been replacing some terrible crumbling rubber cable in the upstairs lighting circuit of my new (to me!) house. I didn't mean to, but on replacing a broken light switch found this appalling wiring - odd because all other wiring in the house is more modern pvc (ring main is white pvc and downstairs lighting 1.5mm grey pvc).

Anyway, I notice that the conduit running down the walls to the switches is metal with no obvious earth - well, there wouldn't be, it's old two-core cable.

The thing is if I replace the backing box with the new ones that have an earth connection point and the conduit is in contact with the box, is that sufficient? And I assume I have to make an earth connection between the earth connection point in the switch and the connection point in the box (fiddly)

 

[Alarm]

Someone will be along soon but that sounds like VIR and needs replacing pronto since you have disturbed it.

 

[xr4x4]

Best to run new chases for the cables.

 

[RF Lighting]

There's no need to earth the conduit. It's not an ECP.

If you can earth it then great, but if not, don't worry about it.

 

[securespark]

However, you do need to replace the rubber with PVC that includes a CPC...

 

[MarkTravis]

Excuse ignorance but what is: ECP and VIR? ........ and CPC!

I am in the process of replacing the rubber cable being held up by the fact that the loft is a foot deep in loose-lay insulation of a fiberous nature requiring mee to get a full protective suit, goggles gloves and breathing mask!!! - I only needed to replace a bloody light switch

 

[xr4x4]

Vir is rubber cable, cpc is an earth.

Dunno what ecp is.

 

[EFLImpudence]

Extraneous Conductive Part.

 

[sparkwright]

You need to check everywhere for old rubber/VIR cable. Look in every switch and light fitting.

Then check the whole of the loft in case there is some up there which hasn't been replaced.

Looking at the consumer unit area may also indicate some old rubber cable.

You don't want any of this old cable in service left in your house.

Going off on a tangent, but occasionally find some old rubber cable in houses in excellent condition, probably later from late 40s and early 50s.

Usually it's absolutely shot to b*****y though.

 

[Taylortwocities]

Check out //www.diynot.com/forums/electrics/lovely-is-it-not.297700/ for a good picture of rubber insulated cable in a bad way.

 

[JohnW2]

There's no need to earth the conduit. It's not an ECP.

Exposed-conductive-part = "Conductive part of equipment which can be touched and which is not normally live, but which can become live when basic insulation fails."

With single-insulated singles in metal conduit, I can't see there is any doubt that the conduit is an exposed-conductive part. However, I'd always understood that even insulated-and-sheathed cables (e.g. T&E) also were only regarded as having 'basic insulation' - in which case (per the BS7671 definition) I would think that the conduit would again be an exposed-conductive part. Am I wrong (not unusual!)?

Kind Regards, John.

 

[JohnW2]

Extraneous Conductive Part.

The conduit is certainly not that, I agree, but what about exposed-conductive part (see my reply to RF)?

Kind Regards, John.

 

[Adam_151]

I would consider conduit to be and exposed conductive part even when carrying 6242Y. Its insulated and sheathed, not double insulated.

The same goes for traywork, if its got 6242Y on it I want to see it earthed, if its only carrying SWA or MICC then not too concerned (i've seen too many instances of 6242Y rubbed through when someone has dragged an armoured over the top of it to think that having an unearthed tray would be a good idea.

While the risk of damage in conduit is lower, it still doesn't sit right with me, and if the OP did not install the conduit then he will not know how much care has been taken in removing the burrs etc

I know there is an opinion out there (posibly from the NICEIC) that metallic containment to sheathed cables does not count as an exposed conductive part. I am not sure I agree with their intepretation and think that perhaps its a little bit foolish!

 

[bernardgreen]

Applying common sense and experience.

Pulling twin and earth into old metal conduit can result in unseen damage to the cable where both sheath and insulation have been abraded leaving one or more conductors bare and possibly in contact with the conduit.

While direct contact with conduit buried in plaster is not ( easily ) possibly any dampness in the plaster is in contact with a large live electrode making contact with the damp plaster hazardous.

 

[EFLImpudence]

Extraneous Conductive Part.

The conduit is certainly not that, I agree, but what about exposed-conductive part (see my reply to RF)?

I did deliberate about that when I replied as obviously the 'E' also stands for exposed.
Also, in the context of the original question (if 'E' for extraneous) it would be bonding.

If it is thought that the conduit may become live then it may require earthing and the 'E' would refer to exposed.
However, the fact is it is not exposed, it's buried (dampness apart).

The original conduit would have been attached to the back box (and so earthed) but I presume it has become detached.