Long chases of 2.5mm T&E in 20mm oval conduit

[DaveyH]

Hello everyone,

We are in the process of a re-wire (and a re-plumb but that’s another story).

I have only done this socket so far, and I would appreciate confirmation that what I am planning to do is ok regarding regulations and it won't de-rate my cables before I carry on with the rest of the sockets in the house.

Originally I had just tacked the 2 ring main cables to the wall with clips, but I have now decided to run them in 2 pieces of 20mm oval conduit as this picture shows.

Untitled

• DaveyH
• 21 Feb 2009
• 4

The idea is to make any future rewiring project much easier and more importantly much CLEANER (ie no chasing).

The cable is just your standard 2.5mm squared twin and earth cable.

I have read some other posts on this forum and I am pretty sure that what I am doing is ok, but I am not 100% sure. On some other posts people were saying it de-rates the cables because heat generated by current flow is not dissipated correctly into surrounding brick/plaster, however I think this was because the other posters were talking about running 2 cables in just 1 piece of conduit.

PS. The chases are quite long (91 inches).

Thanks in advance

Dave

 

[Click-Sure]

If your going to go the conduit route, why not use it in the ceiling as well, use 2.5mm 6491 (1.5mm for the CPC/earth) conduit singles, one conduit drop down the wall as opposed to two.

 

[aptsys]

There's nothing wrong with your proposal, but your picture showing the earths in the separate terminals reminded me of that topic on high integrity earthing

 

[RF Lighting]

shhhh

 

[Taylortwocities]

Oh no....
He's going to wake the sleeping monster - I'm off to DIY Doc for a week 'till it settles down again...

 

[sparkyspike]

2 pieces of 20mm oval conduit as this picture shows.

Looks more like round conduit

 

[Lectrician]

Looks like oval conduit suished at the end

I would be happy with two cables in one conduit, 20mm is tight, 25mm is more suited.

I would try harder with your chasing on the next one - You should be able to shase a nice tight hole to the box so the only real plstering is the drop. It does take practice, and some walls are easier than others.

 

[DaveyH]

Thanks for your replies everyone.

Lectrician you are quite correct, my conduit is indeed 20mm PVC OVAL squished at the end to fit in the round 20mm holes on the flush fitting galvanised steel backboxes.

On another post on this forum putting 2 wires down 1 piece of conduit was deemed to be a bit of a no no, apparently its because the heat generated by current flow can de-rate the cables. Here is the post I am referring too.

//www.diynot.com/forums/viewtopic.php?t=23807

In a nutshell it’s something to do with needing at least 50% free space inside the conduit for airflow.

 

[sparkyspike]

Looks like oval conduit suished at the end

Well spotted. I stand corrected!

 

[Lectrician]

Two T+E's in one conduit is perfectly fine

They end up grouped in the socket anyway

Grouping needs to be taken account of, but in a typical domestic it is hardly worth considering, especially for two lone cables!

 

[Spark123]

I take it you used the CPC as a cheese wire to strip the wire back? Tut tut tut

 

[oharaf]

I was discussing this technique just t'other day with a mate of mine, it does have some sense to it, thou 25mm would be my preference.

Now then High integrity earthing tell me about it..................

 

[Spark123]

Have a look in the on site guide

 

[bongos]

While sort of still on topic, are fly leads to the metal back box required? Only reason I ask is that I always thought that they were but a spark mate says NIC stipulate that they're not needed.

 

[Spark123]

Providing the back box has one fixed lug and the accessory has the means to earth it via the fixing screw the fly lead isn't required, however I have always fitted them as I consider it good practice.