Metal conduit and plastic dry lining boxes

[rebuke]

Hello,

I help out a local amateur theatre and they've been doing some electrical work over the last few days.

One of the things they've done is installed a few new sockets, and the way they've done this is installed inside a partition wall some metal (20mm) conduit which connects at one end to a metal besa box, which has some T&E entering it via a gland (the lid of the box is accessible for inspection and maintenance etc and the T&E runs vertically down so is in a safe zone), and at the other end connects to a plastic dry lining box with a 13A double socket mounted in. The conduit also has a T which goes off and emerges on the surface across a perpendicular wall, and goes to a surface mount 13A double socket.

My concern is whether the conduit where it meets the dry lining box needs to be connected to the CPC in some way - with a metal back box it would obviously pick up the CPC from that, but in this case it won't. The conduit as a whole should pick up the CPC from the surface mount socket, but my understanding is this doesn't comply alone - to comply with regs do they need to put e.g. a suitable ring between the conduit bush and the conduit and attach a CPC to it?

 

[sparkticus]

From your description it sounds like the conduit is being used for mechanical protection only. It is not providing the CPC function since that is provided for (I hope) in the T&E.

The conduit should be securely connected to earth potential at one end since it appears to be a candidate for "extraneous conductive parts" but other than that I don't see a problem.


If the conduit was carrying singles without a CPC then that would be another matter and would obviously be a big problem.

 

[ricicle]

Theatres require licences to operate. Are the people doing the electrical work competant to do so ?

 

[Adam_151]

The conduit as a whole should pick up the CPC from the surface mount socket, but my understanding is this doesn't comply alone - to comply with regs do they need to put e.g. a suitable ring between the conduit bush and the conduit and attach a CPC to it?

If the conduit is mechanically sound at joints etc and the paint has been removed around the joint to this surface m/clad outlet then it should be solidly earthed through this... A single earth lugged to the back of the BESA box and dropped into the socket below would be belt and braces though.

Bit rough making metallic conduit off into a dryline box, and can't understand why it was done, concealed conduit systems are installed at first fix when the stud is up but the plasterboards arn't on, metal k/o boxes are also installed at this stage and mounted on noggins, to acheive a dryline box on the end of the conduit would surely involve more messing about to acheieve a poorer result

 

[holmslaw]

..

 

[sparkwright]

The besa boxes have an earth terminal, so I would like to think an earth wire is connected here, preferably at each besa box.

 

[sparkticus]

The jobs got dangerous bodge written all over it, due to the incorrect use of incompatible materials.

Yes, I would tend to question why they did not install the conduit comprehensively. If professional you are either going to to the job in conduit or choose another method but not half & half. It would be good to see a picture.

 

[sparkwright]

I can only assume the plasterboard was already fitted, most of the installation is meant to be in metal conduit, and this was the easiest way to conceal the wiring where the sockets are. Not ideal, but if done properly it might be quite acceptable.

 

[Risteard]

The conduit should be securely connected to earth potential at one end since it appears to be a candidate for "extraneous conductive parts" but other than that I don't see a problem.

Metallic conduit is an exposed (not extraneous) conductive part, and hence must be earthed.