What is the proper way to run cables in conservatory?

[pike]

Before I start pouring concrete/laying bricks can anybody give me advice as to how best to run the cables to sockets in a brick dwarf wall conservatory.
It is intended to extend the ring main from the house , the dwarf wall will be insulated so is it best to run plastic conduit in the cavity?
What is the normal practices when the cable needs to cross the door aperture?

Thanks

 

[ban-all-sheds]

the dwarf wall will be insulated so is it best to run plastic conduit in the cavity?

Yes.

What is the normal practices when the cable needs to cross the door aperture?

Put it at waist height so that there is no danger of anyone either tripping over it or strangling themselves. Except small children, I guess.

Or if you really must, bury it in earthed metal conduit.

 

[mapj1]

More seriously if cables cross not using lines of least surprise, then the use of SWA might be easier - you can bury it in the wall/floor with impunity, and once you have mastered the glanding, and remember to link the earth to the socket back boxes, it can be much less hassle.

 

[Lectrician]

I assume by brick, you mean unplastered facing brick??

If you do flush boxes into the wall as you build, when you come to second fix you need to be sure there is no gap left around the socket at the mortar joints.

I have seen it done so many ways, but If you can build the inner skin before the outer, you could run conduit around the inner skin in the cavity. Use 20mm round tube, fixed with galv saddles (loose the spacer bar part of the saddle). Use terminal boxes directly behind the socket to ensure the cables are well protected. Put your T+E in the tube, no need to tube through the wall.

Doors....umm.

Another way often seen with brick faced walls is SWA under the screed, through the wall into the cavity, cleated up the inner skin to a galv U box (in and out). 20mm conduit bushed into the galv box and into the socket box through the wall. Strib the SWA long enough to pass right through from the gland into the socket. Use 3 core, and dont worry about earthing the galv box's, just earth the armour at the origin.

Not an ideal way, as the glands are lost for good. Seen it done a few times though.

Better option - plaster the wall

 

[Lectrician]

RE earthed galv conduit.

Yes, done properly, you can then run cables pretty much where you wish. A DIY approach to steel conduit is often to simply cut the conduit, and earth one length to the next with bonding clamps - ABSOLUTE CRAP! I have seen conduit used to protect a cable, only to infact damage it due to chaffing.

Not really a diy thing, steel conduit.

 

[elfreddo]

The easiest method is to run the cables inside the dwarf wall and rest it on top of the insulation, doing away with running it in conduit.
Each back box can then be fed through the knock-out at the rear of each box to the next etc.. clearing insulation behind each socket.
This method is well used as long as the insulation is standard fibre glass.
Door openings are a simple case of feeding the cables through 25mm plastic conduit and sinking them below floor level at the openings, doing away with time consuming SWA termination.

 

[Lectrician]

Bodge

 

[Big_Spark]

Bodge

Got to agree with Lec there, most cables are damages by Insulation. Fibre glass and Polystyrene cause the plasticisers to leech out of the insulation causing the material to break down in about a five year period.

Plastic Conduit will be the best method for a DIYer as embedding SWA directly in concrete is also a bodge as the lime in the concrete will also damage the PVC or XLPE insulation of the SWA.

 

[ban-all-sheds]

I thought fibreglass was just thin glass fibres - how could they leach plasticisers?

 

[Big_Spark]

I thought fibreglass was just thin glass fibres - how could they leach plasticisers?

It is more than the simply glass as we normally think of it, but as I am not a chemistry major I am not sure of the chemical reaction, I think it is catalyst in action though. I have seen cables that appear "burnt" after being left in contact with fibreglass.

I suppose it is possible a chemical used to treat the glass fibre material as oppose to the glass fibres themselves though.

 

[elfreddo]

Chaps
Why then, are there calculations/installation methods, for cables enclosed/touching insulation on one side in the holy Regs??
I agree with polystyrene insulation having adverse affects with pvc t&e
but as said earlier if standard fibre glass is being used "the cables can rest on top of the insulation".

 

[Lectrician]

I have no probs with the contact issue with F/G, celotex and the like, yes. But cables left 'floating' in a cavity (or 'resting') is still a bodge in my view.

 

[ban-all-sheds]

I thought fibreglass was just thin glass fibres - how could they leach plasticisers?

It is more than the simply glass as we normally think of it, but as I am not a chemistry major I am not sure of the chemical reaction, I think it is catalyst in action though. I have seen cables that appear "burnt" after being left in contact with fibreglass.

I suppose it is possible a chemical used to treat the glass fibre material as oppose to the glass fibres themselves though.

Actually, I did wonder, after posting, if the term "fibreglass" in the context of insulation was being misused in the same way that it is when people talk about fibreglass cars, boats etc....