Jobsworth

[JohnW2]

I would be interested to know what the scheme/body would do with this information.

Nothing, I imagine (apart, hopefully, from keeping it), unless perhaps they felt that its contents revealed unacceptable practices (in which case it might shoot the electrician concerned in the foot!!). I was just thinking that the super-cautious/'paranoid' amongst us might want to have a copy of the documentation (with the caveats) 'lodged' somewhere - just in case the customer conveniently 'lost' theirs. I suppose you could send a copy to your solicitor 'for safe keeping'!

Kind Regards, John

 

[mfarrow]

Well, you can't actually have ADS without a CPC. However, that aside, it doesn't seem to stop many electricians doing 'appropriate' work (e.g. replacing plastic switches/roses/light fittings with plastic) on a lighting circuit which has no CPCs - indeed, there is even 'official' guidance about doing such work.

The intention is to have ADS. Regards 'appropriate' work, the guidance is there to allow the installation to have a level of fault protection applied which is equivalent to double or reinforced insulation. OK we still retain the metal back boxes but I don't agree with that practice.

What you say is probably ('literally') true. However, we were talking about buried, inaccessible, cables (buried in plaster I think). In terms of common sense, do you really believe that having a PVC sheath on such cables would result in the installation being appreciably 'safer' ('less dangerous')?

The plaster is not part of the electrical installation. If someone starts chipping at the plaster and puts the bolster through the insulation then it becomes a problem, and the law stops applying common sense at that point.

That is why one would annotate the documentation appropriately (and keep copies, and, if you wanted, send copies at the time to any relevant people/bodies!)

By which time it's gone round the pub through the family tree and back down to your future job list.

 

[JohnW2]

... it doesn't seem to stop many electricians doing 'appropriate' work (e.g. replacing plastic switches/roses/light fittings with plastic) on a lighting circuit which has no CPCs - indeed, there is even 'official' guidance about doing such work.

... Regards 'appropriate' work, the guidance is there to allow the installation to have a level of fault protection applied which is equivalent to double or reinforced insulation. OK we still retain the metal back boxes but I don't agree with that practice.

None of that guidance does anything to give the buried cable 'adequate fault protection' (i.e. a CPC, hence ADS) - and I would remind you that it is the lack of sheathing on the buried cables which is apparently the only reason why the electrician cited in the OP said that he was 'not allowed' to change the light switches.

I continue to feel that an issue pervading most of this discussion is a paucity of 'common sense'.

Kind Regards, John

 

[mfarrow]

None of that guidance does anything to give the buried cable 'adequate fault protection' (i.e. a CPC, hence ADS)

I think the guidance makes the (possibly wrong) assumption that the cable doesn't utilise ADS as it's fault protection, because you are unlikely to find a cable which is protected against fault by ADS. Circuits run in singles in metal conduit are something different of course but are more likely to be earthed from the outset.

 

[JohnW2]

I think the guidance makes the (possibly wrong) assumption that the cable doesn't utilise ADS as it's fault protection, because you are unlikely to find a cable which is protected against fault by ADS.

What are you suggesting does provide cable with fault protection, then?

Kind Regards, John

 

[mfarrow]

What are you suggesting does provide cable with fault protection, then?

Double or Reinforced insulation by means of the sheath, as per 412.2.4.1 (ii) (a).

The presence of a CPC is purely circumstantial to the protective measure of the cable (wiring system). The cable acts as a conduit for the CPC to be utilised at accessories.

 

[JohnW2]

What are you suggesting does provide cable with fault protection, then?

Double or Reinforced insulation by means of the sheath, as per 412.2.4.1 (ii) (a).

I think there is some 'talking at cross purposes' afoot here - you appear to be talking about 'basic protection', not 'fault protection'. The latter is essentially just ADS, as per requirements defined in 411.8.3.

Kind Regards, John

 

[mfarrow]

I think there is some 'talking at cross purposes' afoot here - you appear to be talking about 'basic protection', not 'fault protection'. The latter is essentially just ADS, as per requirements defined in 411.8.3.

411 is the section on ADS. T&E etc apply Double or Reinforced Insulation as per 412, where 411.8.3 does not apply.

 

[JohnW2]

411 is the section on ADS. T&E etc apply Double or Reinforced Insulation as per 412, where 411.8.3 does not apply.

That's all essentially true, but it doesn't alter the fact that you appear to have been using the phrase 'fault protection' to mean something different from what BS7671 means by it. .... and it certainly doesn't alter the things I've said about actual topic of this thread.

Kind Regards, John

 

[mfarrow]

you appear to have been using the phrase 'fault protection' to mean something different from what BS7671 means by it

How so? Fault protection as defined within BS 7671 as:

Protection against electric shock under single-fault conditions

Fault protection of the wiring system is provided by supplementary insulation of the cable when using T&E, per the protective measure of Double or Reinforced Insulation and 412.1.1 (i).

If the sheath has been removed before it enters the earthed accessory ( which uses the ADS-protective measure) then the wiring system's fault protection has been lost.

 

[EFLImpudence]

Fault protection of the wiring system is provided by supplementary insulation of the cable when using T&E, per the protective measure of Double or Reinforced Insulation and 412.1.1 (i).

I think that is where you are going wrong.
Cables aren't classed as 'double insulated' like appliances, they are 'insulated and sheathed'.
The sheath is to physically protect the wires not to prevent shocks.

If the sheath has been removed before it enters the earthed accessory ( which uses the ADS-protective measure) then the wiring system's fault protection has been lost.

Does the wiring system have fault protection in the sense that it stops people receiving a shock when an exposed-conductive-part becomes live?
Does it have exposed-conductive-parts?

 

[JohnW2]

How so? Fault protection as defined within BS 7671 as:

Protection against electric shock under single-fault conditions

Fault protection of the wiring system is provided by supplementary insulation of the cable when using T&E, per the protective measure of Double or Reinforced Insulation and 412.1.1 (i).

Indeed so, but ....

Note: For LV installations, systems and equipment, fault protection generally corresponds to protection against indirect contact ... Indirect contact is "contact of persons or livestock with exposed-conductive-parts which have become live under fault conditions"

In the context we are discussing (cables), I'm struggling a bit to understand which exposed-c-ps "which have become live under fault conditions" you have in mind.

Kind Regards, John

 

[mfarrow]

Cables aren't classed as 'double insulated' like appliances, they are 'insulated and sheathed'.
The sheath is to physically protect the wires not to prevent shocks.

They do not and cannot carry the DI symbol and are termed insulated and sheathed by their own standards, but there is nothing in the BGB which indicates that "Double or Reinforced Insulation" cannot be applied as the protective measure. The sheath is there to provide protection in the event of failure of the basic insulation as required. They have set standards to meet and must be of a certain thickness to comply.

You're quite right that in a cable where double or reinforced insulation is present, there are not generally any exposed conductive parts which aren't themselves protected by ADS, but you could of course count the uninsulated CPC as one if you chose to chop it off either end, as you may find in a lighting circuit without adequate earthing.

There are also situations in a wiring system where exposed conductive parts are present outside the actual cable, and hence where the sheath is required as the protection against fault on those parts (I'm thinking cable capping).

BS 7671 seems to mix and match its terms a bit when reading 412 in isolation, and I might have been wrong to suggest that taking off the sheath voids the cable's fault protection if the exposed conductive parts inside don't actually need protecting, however there may be a requirement in this installation still if a metallic cap has been applied over the unprotected cores.

 

[JohnW2]

You're quite right that in a cable where double or reinforced insulation is present, there are not generally any exposed conductive parts which aren't themselves protected by ADS, but you could of course count the uninsulated CPC as one if you chose to chop it off either end, as you may find in a lighting circuit without adequate earthing.

That's stretching things (and definitions) a bit - but surely the point here is that even if (as per this thread) both the live conductors were only single-insulated one would not expect the CPC to be a (separate) bare conductor, would one?

There are also situations in a wiring system where exposed conductive parts are present outside the actual cable, and hence where the sheath is required as the protection against fault on those parts (I'm thinking cable capping).

If the capping were exposed and had only single-insulated conductors beneath it then, yes, it would be an exposed-c-p which would need to be earthed.

BS 7671 seems to mix and match its terms a bit when reading 412 in isolation, and I might have been wrong to suggest that taking off the sheath voids the cable's fault protection if the exposed conductive parts inside don't actually need protecting,...

That was my point.

... however there may be a requirement in this installation still if a metallic cap has been applied over the unprotected cores.

As above, I total agreed that if there are single-insulated conductors beneath an exposed metal capping, then that capping must be earthed - but that's just 'standard' for any 'Class I' situation.

Kind Regards, John

 

[sparkwright]

You're quite right that in a cable where double or reinforced insulation is present, there are not generally any exposed conductive parts which aren't themselves protected by ADS, but you could of course count the uninsulated CPC as one if you chose to chop it off either end, as you may find in a lighting circuit without adequate earthing.

That's stretching things (and definitions) a bit - but surely the point here is that even if (as per this thread) both the live conductors were only single-insulated one would not expect the CPC to be a (separate) bare conductor, would one?


Kind Regards, John

I gather at the start of this thread, there was a mixture of single insulated singles, and twin+e cable where the sheath does not enter the box, both buried in the wall without conduit. So one may expect the CPC to be a bare conductor.