conduit 20mm plastic and 2 x 2.5 T&E or singles

I'm helping putting a ring main in an integral garage , then an electrician will signoff and connect the tails to a new consumer unit they fitted a few weeks ago
They have agreed to test and connect , but as expected offering little advice on installation, which is understandable as it is there living, I just want to make sure its all right and partp compliant and need to save some money on installation

if i run in 20mm black conduit, for neatness and looks , then where i drop down from ceiling to socket, i will have 2 x 2.5 T&E in one 20mm plastic conduit

Will that have enough spacing and still be rated for 32A or will it be derated ?

Otherwise if i use singles, thats 6 in the 20mm plastic conduit , so same question

BUT with singles, I have to go out the consumer unit in plastic trunking then through a wall - do i have to use conduit in the wall so its protected, and are singles OK in truncking
Hence why I thought 2.5T&E would be better

7 double sockets , garage is a domestic single unit part of house - the length of the garage max would 10m and 3m wide at most , dropping 1.5m at most

Plastic conduit along the wall by ceiling joists
A Box or T junction to drop down the wall to sockets

a SPUR from one socket to a waterproof socket outside

If i use 25mm , i will still have to drop the size down to 20mm for the box knockout
and the T junction

Searched and searched and cant find an answer

If this chap is signing your work off I think you need to ask him!

ok, thanks,
i suspect it will be more like, you should not have done it this way, although I understand the need to make a living, and then £70+vat an hour r to correct , sort of defeats the object

I will use the singles for ringmain and used the tables to work out conduit factors now

so as your unable to provide any assistance .for the latest rules , thanks for replying so promptly anyway

T & E is very hard work in conduit, you'll struggle to get 2 runs in 20mm.
Electrician who did my garage recommended singles in plastic 20mm conduit (2.5 for phase and neutral and 1.5 for earth). That was a squeeze in the drops as well, 25mm would have been much easier but then there's the faff of reducing into the back boxes.

Yes singles are fine in minitrunking, use T & E for your spur through the wall.

If the route from the CU to the garage is a pain for conduit/trunking then use T & E to an adaptable box then conduit from the box onward (usually 4mm T&E will be adequate but make sure your spark is happy with that).

Trunking is fine in a garage, you can use one about as tall as a socket, "dado trunking" and put sockets and switches in it wherever you like, very easy to alter, install or add more. You can use T&E which is cheap and readily available

Run it above workbench height.

https://www.tlc-direct.co.uk/Main_Index/Trunking_Pvc_Index/

eta said:

ok, thanks,
i suspect it will be more like, you should not have done it this way, although I understand the need to make a living, and then £70+vat an hour r to correct , sort of defeats the object

I will use the singles for ringmain and used the tables to work out conduit factors now

so as your unable to provide any assistance .for the latest rules , thanks for replying so promptly anyway

Click to expand...

Not that I don't want to offer assistance just odd he'll sign off the work without any input on how it's installed! How are the sockets laid out, could you post a simple drawing plan?

Thanks to all
"Johnd" - doesn't want to use trunking, due to wanting a black colour (we cant find black trunking easily) and so we need to use the black conduit - the look is very important , but thanks

Yes, but they said you put all the installation cabling work together and we will come and TEST & connect the tails into the consumer unit, so I'm sure if they dont like it , they will just charge to put it right £70+vat / hour, but i hope to talk tomorrow on our plans
Which now is

the plan, sorry dont have a diagram yet, still working with some crayons

Ring main for Integral garage running 7 double sockets , all connected via 20mm trunking using single wire - 2.5mm for live and neutral & 1.5mm for earth. As suggested above

I will either take the 20mm through the wall into the trunking next to the CU or use some 2.5 T&E to connect into a junction box, as suggested above- Thanks "oldbutnotdead" but I can run the 2x 2.5mm so dont need the 4mm

The ring is going around the garage at ceiling joist height , so will have those 3 wires in, and then 20mm drop using a T junction into the double sockets , so again 6 cables in the drops. 6 double sockets in total around
looking at the table on TLC website https://www.tlc-direct.co.uk/Book/4.5.3.htm - the 2.5mm stranded rating is 30 , assuming all 6 were 2.5mm then thats 180 - the length for Double socket up and over and back down to next socket at the longest run is about 4 meters and 2 bends
The tables say figures for that 4m2b is 213 - so 180 is less then the 213 and so we should be OK with 20mm conduit, other lengths will be 3m or 6m straight but will only have 3 singles in as we are going around the whole ceiling in a circle.
Then off of 1 double socket - I will add a Fused spur with 2.5T&E in 20mm trunking to an outside waterproof socket as a spur, the only one off the ringman.

for just a very short section 1.5m straight - will have 1x 1mm T&E lighting cable & 2 x 2.5 & 1.5 single stranded , so well below the 460 figure from the table

IF , i have interpreted the rules and tables correctly

garage is 5m long x 2.5 mm wide - so trunking all round the ceiling and then through a wall to back of consumer unit trunking - With 6 drops down about 1 to 1.5m to all double plugs sockets
one spur out to the outside wall , and fused that can be isolated so can be isolated

FOR THE LIGHTING
Lighting using 1mm T&E cable & 3core T&E between 2 switches for dual on/off , in a separate 20mm conduit run - except for a small 1.5m section , that will have 1mm T&E and 3 singles of the ring main.
Lighting panels are just under 50W (46W) each and we will have 4 of them , all radial with one switch , all going to be run off a seperate garage lighting CU fuse so actually less than 200W for all lighting.

The CU was updated only 2mths ago - and a lot of house rewired and seperate rings added and the rest tested , by the same electricians, so already spent well over £1000 and money is tight now.

I hope to put a drawing together tonight, BUT looking after grandchildren , where the work is also being done

Thanks to all for looking and considering questions and advice

I'd be inclined to do everything in conduit with singles. There's little difference really in cost between 25mm and 20mm, so easy to do 25mm round the main route and 20mm for the drops. 4x2.5 and 2x1.5 singles fit easily into a 20mm conduit, especially just a straight drop into a socket.
Note that if you use singles, then the containment must meet IP4x or IPxxD which trunking may not meet without additional parts. Plastic mini trunking won't do since (IMO) the lid (especially a joint/corner cover) is removable without a tool (depending on various factors) and it can be difficult to get all the joints to IP4X or IPxxD. Galv trunking needs additional parts as the best the manufacturers claim is IP3x (at least, Unitrunk do IIRC).

Thanks so much for the info
we have purchased
https://www.screwfix.com/p/tower-co...ck/7980p#product_additional_details_container

How would i go from 25 to 20 mm dont see any adapters to downsize on screwfix
we are only doing 4m of lighting , so 100m of 1.5 Brown, & Blue is a lot more expensive then 10m of 1mm T&E

Dont use T boxes use a plain 3x3 pvc box, drill 25mm each side and 20mm out the bottom, using relevant end adapters on the conduit ends.
Personally in my view all 3 cores should be 2.5 in singles but im sure others will disagree

Reducers are readily available if you go to a decent outlet. With these, you use a 25mm conduit box, the adapter goes into the socket then the smaller conduit goes into the adapter.

Have you considered installing radial(s) instead of a ring. Just curious, but why so many sockets in a garage?

thanks for the reply
The garage will also be used as a workshop, so two over that , and have 2 electric 500W garage door motors , 2 over the workbench, a freezer various domestic and tool rechargeable items, , then for some power tools SMS , etc - just wanted to make sure we had enough for future
And to make the ring is just a return of about 3 meters back to the CU
, so no big issue for the ring and dropping an extra double in case

When my electrician and I wired up my garage, we had no major issues installing 2x 2.5mm T+E in 20mm conduit. As long as it comes straight off the roll, it should be fine.

We only used conduit up to the roof timber height, and then just clipped it, as conduit up there was a little bit pointless and more work.

As you are installing a new circuit, this is notifiable. The electricians can only give you an EICR, not notify the job. Given your stated requirements, I’d consider fitting a small CU in the garage so you can separate the circuits. Given a choice, I go with radials every time.