I'm building a timber frame outbuilding - basically 2"x4" frame with ply and oak cladding on the outside and OSB or ply inside. I'll obviously be using a Part P electrician to do the electrics but haven't got one lined up yet.

To cut a long story short...Does wiring in this sort of structure have to be done in conduit on the inside or can it be done with bare cable in the frame before the inside is lined with OSB? It makes a difference as to when I get an electrician out.

obviously conduit would be lovely for rewiring, mechanical reasons, but are these walls or structure going to be any more onerous (is that the correct word?) than a normal stud wall?

Out of curiosity are the walls insulated?

CWatters wrote on Sep 18^th, 2009, 7:58am:


Didnt realise they made em  

sparky415 wrote on Sep 18^th, 2009, 6:59pm:


No it's just a garden store/potting shed.

Quote:


Just uncovered a section and unfortunately it looks like 2.5mm. It's marked 3 x 2.5. So existing circuit looks like this..

20A RCD (or do I mean an RCBO?) in house CU
approx 18 meters of 2.5mm to get to outside wall
Junction box inside
approx 20 meter armoured cable marked 3 x 2.5
Single 13A MK masterseal socket

If that were to be extended to the new building by the most obvious route the armoured cable would be approx 43 meters (gulp) making a total of around 61 meters each way in 2.5 mm.

Google says the resistance of 122 meters of 2.5mm is around 0.87 Ohms.  At 20A that's a voltage drop of 17V which I think is more than you are allowed? Oh bother.

If the cable took a short cut across the lawn the total length would be a bit shorter at around 55-56 meters each way.  Resistance would be 0.8 for a 16V drop so I don't think that works either.

Am I thinking on the right lines or have I missed something?

Quote:


Ah yes hadn't thought of that. I guess I could disconnect the old one.

Its probably an RCBO,

Sounds like you will need a new SWA mate
You can please yourself with what you allow for
Personally I would put in a 6mm 3 core (4mm min)