Round vs oval conduit

DJ12345 · Apr 26, 2025

Hello guys! Just quick question, whats better to be buried inside the wall? Round or oval conduit for easy cable management and replacement? I have seen people using round conduit inside the wall but i am not sure if they are right as i have heard from other people that are oval conduit. Whats your thoughts?

Thank you!

brianmoooore · Apr 26, 2025

20mm oval conduit 99% of the time.

littlespark · Apr 27, 2025

I would think oval conduit was invented just for being buried in the wall. You wouldn’t run it surface as you would 20mm round.

Also, you don’t need to chase the wall so deep which could be structurally weakened if you go too far.

HappyHippyDad · Apr 27, 2025

DJ12345 said:
Hello guys! Just quick question, whats better to be buried inside the wall? Round or oval conduit for easy cable management and replacement? I have seen people using round conduit inside the wall but i am not sure if they are right as i have heard from other people that are oval conduit. Whats your thoughts?

Thank you!

Oval conduit is easier as you don't have to chase out such a deep hole. Having said that, I have never tried round conduit in chases, perhaps it has some advantages that I am unaware of.
I 'think' the oval conduit may have an ever so slightly bigger cross sectional area as well.
CSA of 20mm round conduit is 31.4 sq mm
The CSA of an ellipse (a perfect oval) which has 25mm long side and 16mm short would also be 31.4 sq mm, but oval conduit has sharper corners than an ellipse, meaning slightly more area (I think, just by looking).

Also... The triple blade metabo wall chaser takes out a perfect 25mm to squeeze 25mm oval conduit into

7029 dave · Apr 27, 2025

IMO oval tube is used in domestic situations I always use it. If a client wanted the potential to be able to rewire with minimum disruption and mess I would use 20mm round full conduit system in singles. Only disadvantage with this is its much harder for any alterations not that its impossible. More expensive too

Simon47 · Apr 27, 2025

Oval is a lot thinner wall as well. As said, designed to minimise the depth to bury it.
It's fairly easy to flex the oval, for example when you get to the box and need to bend it into the wall a bit to match the holes in the box - I NEVER stop the conduit short and dogleg the cables. Doing that with round would need somewhat more effort to set it.

brianmoooore · Apr 27, 2025

In most cases, I bring the oval conduit a few mm into the box, securing it with a dab of building adhesive if I think there's a chance it might get dislodged by 'other trades'.

Simon47 · Apr 28, 2025

Nice to see I'm not alone

7029 dave · Apr 28, 2025

I will fess up when I bring the oval into a box a few mm in don't bother with a cromet

Simon47 · Apr 28, 2025

If the conduit enters the box, a grommet isn't required as the conduit will provide protection from the (usually sharp) metal edge.

brianmoooore · Apr 28, 2025

More importantly, if there's no grommet there, it can't be dislodged.

littlespark · Apr 29, 2025

The old 12mm deep switch back boxes had a rolled edge to their oval hole on the top.
Didn’t need a gromet there.

UNG · Apr 29, 2025

littlespark said:
The old 12mm deep switch back boxes had a rolled edge to their oval hole on the top.
Didn’t need a gromet there.

Not all of them did have the rolled edge it I remember it was only 1 or 2 manufacturers that did it

littlespark · Apr 29, 2025

You might be right. Some were rolled, some were an ovel knockout... which then needed a grommet....
Am i right in thinking there was oval grommets.... or just squashed round ones?

UNG · Apr 29, 2025

littlespark said:
You might be right. Some were rolled, some were an ovel knockout... which then needed a grommet....
Am i right in thinking there was oval grommets.... or just squashed round ones?

Again I recall some did have a grommet already fitted when you purchased them if they were round grommets that had been squashed I don't know / can't remember

brianmoooore · Apr 29, 2025

Some had rolled edges, but the rest, to the best of my knowledge, came ready fitted with an oval rubber grommet.

7029 dave · Apr 29, 2025

UNG said:
Again I recall some did have a grommet already fitted when you purchased them if they were round grommets that had been squashed I don't know / can't remember

Yes some did have cromets already fitted

Marvo · May 2, 2025

I've never even seen oval conduit but I'm not a domestic sparky. How would you bend oval conduit, I'm assuming there's no such thing as an oval spring bender....?? Do you get oval male adaptors and other such fittings? I could see it reducing the depth needed for chasing but I'd imagine at a large trade-off.

littlespark · May 2, 2025

You don’t/ can’t bend oval conduit… and I think it was developed just for cable drops in chases as an alternative to capping over the top…. With the benefit of being able to rewire through it (if not too packed with cable)

Marvo · May 2, 2025

Ah..okay. When we wire a domestic house in conduit it's continuous PVC tubing between the back boxes so you can pull new wires between two sockets or switches or luminaires at any time in the future. Sounds like you don't use conduit that way. Are you guys using steel oval conduit drops as protection? I though that's what your cable zone rules were there for..??

7029 dave · May 2, 2025

Marvo said:
Ah..okay. When we wire a domestic house in conduit it's continuous PVC tubing between the back boxes so you can pull new wires between two sockets or switches or luminaires at any time in the future. Sounds like you don't use conduit that way. Are you guys using steel oval conduit drops as protection? I though that's what your cable zone rules were there for..??

In singles no doubt

Marvo · May 2, 2025

7029 dave said:
In singles no doubt

In singles or flat twin+e cable

littlespark · May 2, 2025

Oval is really just for drops…. So it’s our twin and earth cables as standard, and then run vertically through the oval conduit to the boxes.

Older houses could still have steel conduit and wired in singles… old imperial sized conduit.

Simon47 · May 5, 2025

littlespark said:
You don’t/ can’t bend oval conduit…

You can, but it's a p.i.t.a. to do.
Tape over one end, fill with sand, apply hot air from gun, and ease it round. The sand stops it just completely flattening, but it still needs patience. I find just heating the outside of the bend, and not doing it in one go (bend, straighten a little, bend, straiten a little, ...) helps as it allows the sand to settle a bit each time - if you are stretching the outside, it means the volume is increasing so need to allow the sand to settle and fill it.
Works bending either way - on the wide or the thin face.
We bother ? In our lounge I had to bend the conduits out of the wall and notch the wall plate - otherwise they'd just but onto the top face of the wall plate. In the hallway I needed a 90° bend from coming out the top of the switch backbox to going outside higher up for the outside light.
I hate not being able to alter the wiring, the amount I had to hack out of the plaster in the lounge was ... annoying.

7029 dave · May 5, 2025

Simon47 said:
You can, but it's a p.i.t.a. to do.
Tape over one end, fill with sand, apply hot air from gun, and ease it round. The sand stops it just completely flattening, but it still needs patience. I find just heating the outside of the bend, and not doing it in one go (bend, straighten a little, bend, straiten a little, ...) helps as it allows the sand to settle a bit each time - if you are stretching the outside, it means the volume is increasing so need to allow the sand to settle and fill it.
Works bending either way - on the wide or the thin face.
We bother ? In our lounge I had to bend the conduits out of the wall and notch the wall plate - otherwise they'd just but onto the top face of the wall plate. In the hallway I needed a 90° bend from coming out the top of the switch backbox to going outside higher up for the outside light.
I hate not being able to alter the wiring, the amount I had to hack out of the plaster in the lounge was ... annoying.

Surely it would have been easier to use 20mm round conduit (pvc) and use a spring

brianmoooore · May 5, 2025

I regularly work on houses where 600mm thick internal walls are the norm and 1000mm thick walls not unusual. Door frames tend to be set flush with one side or the other, which leaves the light switches on the non flush side effectively in a short tunnel.
For these situations I use corrugated 20mm round flexible conduit, following the 'safe' zone up from the switch, but from there on , to the ceiling in the room, chased in so far as to be out of the zone.

Simon47 · May 8, 2025

7029 dave said:
Surely it would have been easier to use 20mm round conduit (pvc) and use a spring

Not when you are slotting it in between the brick courses to minimise the amount of hard red brick you need to drill.
Or when 20mm conduit would mean chasing the hard brick while oval will fit in the bonding depth.
Or you're using two 32mm ovals to allow for needed capacity. In that case, I ran them side by side up the wall, and carefully shaped them to be one over the other to minimise to hole I had to drill at around 45° through both skins of a brick wall.
Or ...

That's just the most recent ones that come to mind. In general, you are right, just use round conduit and a bending spring. But there are many situations where oval, and being able to bend it, is going to be a whole lot better.