conduit bending

[Fred]

Hi,

I see you can buy a conduit bending spring. Does this work with plastic and metal conduit? What a shame the conduit is 20 or 25mm and not 22mm otherwise one spring could be used for plumbing and conduit. I dare say there are proper conduit benders but for one-off use, a spring is probably the only sensible way forward. Do you use them as you would with copper pipe: insert spring, bend over knee, and then bend back slightly to release the spring?

I would have thought that big angles, say 90 degrees, were asking for trouble: presumably you make the bends as gentle as possible to aid cable threading?

Is it a good idea to bend conduit or it it better to buy the joins? The corner pieces usually have a lid that unscrews, which enables you to help push cables round the corner when installing/removing them.

What if the conduit was buried inside a wall. Wouldn't I need something behind a blank plate, not only so that I could access the bend but also to show that the cable changes direction? I thought there had to be an "accessory" wherever the cable changed direction?

TIA

[Harry Bloomfield]

Fred has brought this to us :

Plastic only.

You can make bends in steel conduit using a piece of timber with suitable hole in it. The hole size and shape is critical. It needs to be tight in width, to prevent the conduit crushing, yet with a slot in the height to allow it to bend - plus lots and lots of practice.

Pretty much.

Yes.

That will depend upon quantity. The more bends you need, the cheaper the spring will become.

Elbows - they are very tight, but you can also buy less severe 'bends', with or without inspection covers.

[Dave Plowman (News)]

No. Steel conduit requires a mandrel bender.

[John Rumm]

Isn't he in the house of lords now?

[Fred]

22mm? Once but thereafter I used elbows ;)

I need a 90 degree bend (because the stairs are in the way); I don't know how I could do that with oval conduit.

I did think I would bend the conduit but I don't want to have to rip the wall out if the wire gets stuck, so I'm thinking some sort of access would be a good idea. The problem is that conduit accessories don't look very pretty and I don't want to see them sticking out of the wall. I think the best way would be to use a 1G blank plate. Even that's not pretty but its the lesser of all the other evils. But what to put behind it?

I can't use traditional dry wall boxes because they only seem to allow cable to enter from top or bottom, not the sides. But if I use a traditional galvanized back box, wouldn't I need to earth it, even though the cables are only "passing through"?

I have seen some conduit boxes but they only have knock outs top and bottom; not at the side, and I tried drilling both a proper conduit box and a "normal" pattress box and both were brittle and broke ;(

Help!

[Tim Watts]

Fred wibbled on Friday 30 April 2010 14:46

Only 2 ways I know of: Bending oval is just about possible with the application of a hot air gun - but it is very difficult to stop it collapsing. I've put offsets in it but never a 90 degree bend. With enough fiddling about it may be possible but will take a lot of fiddling.

The other way is to joint it into 20mm round using some rather rare adaptors.

[John Rumm]

Not easily - although you could mitre the ends of two bits to form a corner.

Perhaps I am missing something, but why do you need conduit at all? can you not either set the cable directly into the chase and plaster over, or use capping and plaster over? Is there a particular need to be able to pull new wires later? If there is a potential need for additional wires later, could you not lay in spare cable now?

No. You only usually earth back boxes when you will have live connections contained in them.

[Fred]

It's a stud wall but I was trying to be neat and hide all the cable inside. It has to bend because of the stair case. You are quite right, I could put the cable in and board it up, job done. In many ways that would be so much simpler. I just wanted to future proof it. The problem is that not having a crystal ball, I don't know what I might want to add later and you can guarantee that I will need one more wire than I have added! So I just thought using some sort of conduit would allow me to make changes later without having to change the wall the wall later.

Thanks. That is what I wanted to hear. It makes sense to only earth them when there is a possibility that an exposed conductor might touch them.

[John Rumm]

How about using the flexible conduit instead?

would solve your bending problem, although pulling additional wires would still be difficult.

[Tim Watts]

Fred wibbled on Friday 30 April 2010 16:58

Can you not use round conduit then?

[Harry Bloomfield]

Tim Watts formulated the question :

Filling with water and freezing would help stop it collapsing, or packing with sand.

[Harry Bloomfield]

Dave Plowman (News) expressed precisely :

You can actually bend 20mm conduit around your knee, if you are careful and don't get it too tight.