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Metal comduit as cpc

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ryan24

Hi all.

whats people's thoughts on having class 1 switches and fittings on an installation that is wired in old imperial conduit acting as the sole cpc? If there's a fly-lead from switch to back box surely this will be fine? Getting a lot of mixed anwsers on this some saying no good others saying perfectly fine? I personally think it's not a problem as conduit can be the best cpc you get. Any one else dealt with this? Thanks
 
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It is perfectly fine.

It is frowned upon in certain circles, and by certain organisations, and with good reason.
The reason however is very sad.
It is frowned upon as the designers who have often little or no control over how the installation is constructed, are unable to rely on the competence of the installer to get the conduit correctly installed to provide an adequate cpc. Nothing more than that. Hence they add a secondary cpc within the containment in an attempt to ensure that there is at least one functional cpc.
Same reason that using the SWA has fallen from favour as a cpc.
It is simply that the designers cannot rely on the installer to do the job correctly so they design in some redundant safety, by insisting on additional cpc, either within the SWA or additional to.

Simply another reflection on the poor state of the competence in the installation operatives in the industry.

Note terms...
 
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Noob2013 said:
It doesn't help that the new AM2 doesn't cover conduit. It's going down the domestic route so less and less electricians are competent with conduit!!
Click to expand...

Too true!!

[ElectriciansForums.net] Metal comduit as cpc
 
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Just thinking back to my old foreman, he would have beaten me around the head with a large and heavy blunt instrument for wasting time and money with an earth in conduit.

PS.We didn’t have CPC’s back then!
 
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I worked for a company and we worked for John Lewis, the spec was no earth wires.
No this was not in the 1960s but in 2000 in London near brands hatch.

The electrician who I worked with and was my 'mentor' said that it would have to be 'pressure tested'.
So even 'now' you do not need earth wires.
 
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Jay, you never have and hopefully you never will require the additional “earth” in metallic containment.

But as Paul pointed out it comes down to twitchy designers.

The continuity testing your mentor mentioned would be using a Ductor. Pressure testing is totally different.
 
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Metal conduit and swa armouring has to be mechanically and electrically sound (or words to those effect), adding a cpc 'just in case' is wasted material (assuming the job is done properly, which it must be or you wouldn't be adding a cpc would you?)

If pyro was not so expensive I wonder if there would be threads asking if they need an internal core in that in case the sheath is not up to the job....
 
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The metal conduit or metal containment Zs value is not just fine it will generally knock a separate CPC value in to a cock's hat!! There is not a single CPC conductor in any of our conduit installations and this project is a good 85+% conduit install for final circuits!!
 
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