Steel Conduit - How to Install ?

It is generally installed on a case by case basis working your way along the conduit.

In some instances, where the access is tight, it is installed as you say, with the conduit cut to size, bent, threaded and accessories screwed in place. The saddles for the conduit are installed on the wall and then the 'preformed section' screwed in place. Yes some times it takes a couple of people to install a larger section. We would frequently make the conduit in sections, mount up the first section and then make the next section, taking all the measurements from the end of the first section. We would then loosen off or remove the first section to allow the section section to be coupled onto it, then re-secure the first section along with the second. A lot of going backwards and forwards, securing, removing and refitting to get the job done.

However, longer runs of conduit have a certain level of flexibility, so you can fix the box at one end, with one conduit saddle and there will be enough movement in the other end to allow the box to still be screwed onto the conduit at the other end. the box can then be fixed in place and you go back along the conduit securing the remaining saddles.

When using conduit in industry, we will also bend the conduit instead of using boxes to change direction. It looks nicer and the cables are easier to pull through.

Instead of using the threaded conduit boxes, you can also utilise adaptable steel boxes with a clearance hole to put the conduit through with a lock ring either side to secure it to the box. This isn't as water tight as the threaded boxes. We also use brass bushings over the end of the thread on the inside of the conduit box to protect the cables.

As a last resort, you can use the combination of a coupler, nipple and a lock ring. You can screw the nipple into the coupler on the end of the conduit as far as it will go in, put the lock ring onto the nipple, then offer up the conduit box and unscrew the nipple from the coupler into the conduit box, once in far enough it is locked in place with the lock ring. Looks awful after it is done mind you. You can make longer nipples up than standard by threading offcuts of conduit.

It is a real art form on big installations and quite time consuming unless you are constantly using it. Probably why flexible conduit was developed to ease some of the installation into tight areas and ultimately why plastic conduit was developed, that tends to be easier with the glue together concept.

Kind regards

Hi Donald,

A great explanation, thank you, with plenty of tips to try out.

A lot of going backwards and forwards, securing, removing and refitting to get the job done.

It's really helpful to know that rather than push onwards regardless, thinking I must keep adding and not taking a step or two back. Maybe I should opt for the PVC, its much cheaper, but I liked the idea of trying my hand at this....definitely an art form though, just like plumbing copper pipework together

The PVC is cheaper and does not require the same amount of tooling as steel conduit but it isn't as robust mechanically. It is generally easier to assemble as it has quite a bit more flexibility, and is all push fit instead of threading everything together.

It is important to glue joints together that could be pulled apart. i.e. if you have a straight section of PVC conduit between two boxes that are screwed to the wall, then the joints cannot separate. If the conduit has a right angle in it, then the joints can be pulled apart, even when secured with the saddles. In this case it must be glued, which isn't a problem, it is just that if it ever needed alterations, then it gets cut off and discarded, whereas the steel conduit can be unscrewed and reused.

One thing to be aware of with PVC conduit, it that if installed outside in sunlight, it will expand and contract and if extra saddles aren't used, it can end up twisting or warping between the saddles, horizontal sections can sag under these conditions.

If you have a lot to do, then working with steel conduit is well worth learning and there is a lot of satisfaction in the end result, even if there is a bit of frustration in getting there. If it is a one off job, then PVC would be more cost effective.

The only other deciding factor is the mechanical robustness required. If the installation is in areas where there is risk of mechanical damage, then steel is the way to go. Do remember though that steel conduit is extraneous metal work and therefore must be earthed.

Kind regards

Great tips and words of wisdom, thank you three-phase  ....I haven't actually picked up the sections of conduit yet, but I really like the solid approach of steel.

Do you have any advice on how to feed a cable that comes out of the wall into such a setup. I've a Twin and Earth (T+E) cable exiting the brickwork for my external lights but I cannot see if any of the circular boxes available allow cable entry in the back, I don't think they have knock-outs. I could use a gland in the box but it would look messy and a very small bit of that T+E would be vulnerable.

Hi Rod H,

There are no knock-outs on those boxes. If you want or need 'rear-entry' then you need to make a hole and fit a male bush into a female coupling - much like any other conduit termination you would do onto an enclosure for example. The bush goes inside the terminal (circular) box with the male thread protruding out the back, you then screw on your female coupling, and add your piece of conduit as normal.

If you can't get conduit to go through the wall for whatever reason, then you can omit this, and instead install a female bush over the top of your male bush and then run your cable through. You may need a lockring to go over the male bush in order to secure it before adding the female bush.

The female bush has a smooth inner edge and hence won't chaff your cable.

Hope this helps. Sometimes the image in my head doesn't translate to words on a screen!

Hi chunkasmaximus

Thank you for explaining this. Sounds like for a proper install, with the circular box flush to the wall, I'd have to drill a 20mm/25mm diameter into the brick to accommodate that coupling which would (1) leave a unsightly hole should I decide to change the setup and (2) the cable already comes out a small hole between the bricks so increasing that would damage the feed.

In your opinion, would a hole in the back of the round box fitted with a rubber grommet be a reasonable approach where the round box was flush to the wall (e.g. it would remain protected) ? Those boxes also look quite tough when it comes to making a hole in the back !

I know what you mean about the hole in the wall..

You would struggle to get a grommet on there, the metal is usually a bit too thick for the grommet to sit properly. You could try something like grommet strip (https://www.cablecraft.co.uk/halogen-free-black-grommet-strip-12742 ) which tends to be more flexible, but again I think the metal thickness may not allow it to sit properly.

Making the hole in the box shouldn't be too difficult, the material tends to be soft enough to use with step drill bits or hole saws. Cutting fluid will certainly help. If you struggle to do it, it may help to fix it to some secure scrap wood, then drill through it. You should end up with a nice clean hole.

You can then use a short male bush with a female bush to keep the rear protrusion minimal. You would probably only need to chip away a very small amount of brick/mortar to allow flush mounting of the box.

Thank you again for the walk through - I feel like I've accomplished it already !

You're welcome

If the hole in the box is oversized and centred on the cable entry when fitted, then the cable won't be able to touch the 'sharp edge' (which you have already carefully deburred of course...)

If there is enough gap between the cable and wall you could perhaps consider using a rubber sleeve bushing instead of a normal grommet to allow a flush mount. Something of the style: Product LinkProduct Link

You could also perhaps cut a grommet in half or use a nylon bush and bond it inside the box to keep it in place, or press in a soft brass grommet which would dress the edge of the hole with minimal protrusion to the rear.

Not sure wat the reg's have to say though.

If the hole in the box is oversized and centred on the cable entry when fitted, then the cable won't be able to touch the 'sharp edge' (which you have already carefully deburred of course...)

If there is enough gap between the cable and wall you could perhaps consider using a rubber sleeve bushing instead of a normal grommet to allow a flush mount. Something of the style: Product LinkProduct Link

You could also perhaps cut a grommet in half or use a nylon bush and bond it inside the box to keep it in place, or press in a soft brass grommet which would dress the edge of the hole with minimal protrusion to the rear.

Not sure wat the reg's have to say though.