Conduit diameter for socket in brick wall

19 Feb 2015
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United Kingdom
If a 25mm metal pattress, with standard 20mm knockouts, is set into a brick wall, to allow the installation of a standard domestic electrical socket, does the conduit need to be 20mm round conduit? That is, conduit running from floor inside wall up to socket.

Was wondering if conduit of a lesser diameter, (or perhaps a square/rectangular shape) could be used to allow less tracking into wall?

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smaller oval conduit is ok but it depends on the type of cable and how many you want to go to the socket
It would just be one standard double socket, so just the one cable.
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This would be one double socket, and not a single socket.
You can get 2x2.5mm2 in this (screwfix 93233). You can squeeze it so it fits in the 20mm knockout too.

You don't have to use any conduit if its easier...
You can get 2x2.5mm2 in this (screwfix 93233). You can squeeze it so it fits in the 20mm knockout too.

You don't have to use any conduit if its easier...
You can but it is quite difficult to change later. I now use 25mm and file out the back box hole to suit. Saves having a grommet as well.
Why does it need to go in conduit?
It doesn't have to be in conduit, but it makes it a lot easier later on if you want to alter anything (makes it possible to pull cable out and push a different one in). Also, it really helps for the latter if you make sure the conduit actually reaches the box (see Winston's comment above - I have some nibblers that make short work of opening out the holes) - it's common for people to use oval conduit, but then stop it an inch short of the box and dog-leg the cables to go through the knockouts, that's a p.i.t.a. and negates a lot of the benefit of using conduit in the first place.
16 mm conduit was standard for singles, not seen singles used in years, mainly old council houses, but was common.
Singles are still frequently used, but 16mm conduit isn't something you'll readily find. Conduit is invariably 20mm or 25mm these days. You'll never really find 32mm either.
You'll never really find 32mm either.
It's usually in stock (albeit fairly small quantities) in CEF & TLC. Locally we have Edwardes they carry stock and usually 50mm too.
Yet I recall some years ago wanting a larger size and the local CEF branch telling me it didn't exist. With great care I was able to get a couple of multipair and a two tube blown fibre duct (phone & data services) down a straight run of 25mm - but zero chance of adding anything else.
PS thank you very much to the architect for not even considering how to get services around the building :rolleyes:p
So what. That is a foreign country that you don’t even live in.
I do live in Ireland you absolute toilet head. And it's relevant to questions about general availability of sizes other than the staple 20mm or 25mm. They simply aren't widely available.

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