Conduit Drops

[OxiaUK]

Hi,

in my new garage I have some 50x50 plastic trunking all around the perimeter inside at roof level and I plan to drop 20mm conduit down to each switch / socket...

silly question but what is the best way to make sure a drilled hole in the trunking will line up with the conduit once it's mounted with saddles on the wall?

Thanks

 

[crystal ball]

Use a bit of conduit glanded into your accessory with saddle fitted, offer it up to trunking, draw round it, or dab some chalk on the end

 

[333rocky333]

You fail to say Metal or Plastic, with metal. there are numerous types of saddle, Spacer bar, Distance and Hospital, all with varying distances, whereas plastic are usually spacer bar type or there are the plumbing type where the pipe pushes in.

If you have an offcut of the trunking, try it first on that, then use that as a template, to be honest I tend to just quess it by holding the end adaptor Bush up against whatever and marking, you need to leave a gap behind, it though at least, I guess about 7mm for spacer bar.
6 inch pipe with 2 of the saddles on it can also be used
Mark trunking with pencil, then can buff it off after

Bear in mind your limited how near to the back you can drill as the Bush will need to fit INSIDE the trunking, I assume you are fitting end adapters.

Plastic is a bit more forgiving anyway, also the gap for the accessory hole is not always the same as for a saddle, so unless you want to start, double setting the pipe, it may not fit perfectly parallel anyway, but likely not enough to show.

 

[SimonH2]

Of course, once you've worked it out once, you can then either just measure it (i.e xx mm from the wall) or cut a bit of cardboard as a template for marking.

 

[sparkymarka]

Did anyone mention that 25mm is better if your trying to get 2 x 2.5 t&e down the drop ….

 

[crystal ball]

Sockets & switches have 20mm knockouts so they will need opening up if using 25mm

 

[SimonH2]

Did anyone mention that 25mm is better if your trying to get 2 x 2.5 t&e down the drop ….

Or you put the cable in first and assemble the conduit round it.
I.e. put the male bushing throught the hole in the trunking, put the cable in leaving the rwo ends dangling, slide the coupler up and screw it to the bush, slide the conduit over the cables and into the coupler, slide on the bottom coupler, skide on the back box, and finally fit the bush. Bit harder with threaded metal conduit.
The main thing is that you have to remove any twists and keep the two cables flat against each other and then they fit easily down a 20mm conduit - just not round bends etc.
An alternative is to make sure the trunking is IP4x or IPxxD and use singles.
EDIT: for that last bit, the whole containment all the way into the CU needs to be IP4x or IPxxD.
EDIT2: for plastic trunking you shoukd get IPxxD just by using the moulded cover sections for all joints/bends. Unless extraordinariky skilled, you won't get it with hand made joints - and if you do, that will go the first time someone takes the lid off and "chucks it back on".

 

[crystal ball]

A squirt of lube will help things along

 

[333rocky333]

Or you put the cable in first and assemble the conduit round it.

I believe that would contravene the regs though

 

[SimonH2]

What regs does that contravene ?

 

[333rocky333]

What regs does that contravene ?

Well i always thought it was 522.8.2, that said a conduit system should be complete before cables are drawn in, however rereading it, it only applies to systems buried in the structure, so i apologise.

 

[SimonH2]

Ah, that explains the confusion. Quite reasonable for something that's going to be, for example, buried in concrete - if the duct fills with concrete after you've put the cables in then a) you wouldn't know, and b) it could affect the cable that's in there.
But for the sort of conduit runs we're talking about here, the end result is the same. And if you think about it, if that rule did apply to all containments, it would scupper pretty well all the standard first-fix working practices - though some of them deserve to be banned !