Wiring through a garage/outbuilding

[phykell]

I'm wiring my kitchen on a separate circuit to the rest of my house. The kitchen is an extension and is adjoined to both the house and the garage. I want to run power (for ring-main and cooker) and lighting circuit cables through a wall from the CU, into the garage and then along the wall above a doorway (from kitchen to garage) and through the wall into the kitchen.

The quick and dirty method is to follow the example that the previous occupier chose for the cooker circuit - to just dangle the cable from the roof joists in the garage. While this is probably adequate, I was wondering what a more professional approach might be.

The cables can be well out of harms way up in the roof joists but I'd rather not have a load of loose cables. Here's some options I've thought of:

1. Should I screw long boards to the wall up to the kitchen and secure the cabling using cleats?

2. Should I use outdoor conduit? Expensive and probably overkill I would've thought.

3. Should I use trunking? Screwfix do some up to 38mm x 16mm though it's expensive at £30 for 15m and I've got around 9m to do

4. Should I just use PVC channel to cover it?

Note that all options require wood to be screwed to the wall as the wall is "rough rendered" so it's a pain to knock cleats into and rough on the cable.

Also, when routing my cables through the walls, what's the preferred way of doing it? Again, the previous owner just knocked a hole through and left it at that, but I'd like to make a more professional job of it if possible.

Picture here:

http://homepage.ntlworld.com/phykell/diy/GarageInside.jpg

To the right is the garage consumer unit that is being replaced. At the left hand side you can see the door into the kitchen and the end wall through which the cables will pass. You can also see how the existing cooker circuit cable is wired - through the joists.

Any suggestions appreciated

 

[ban-all-sheds]

20-22mm PVC overflow pipe - £9.49 for 30m from Screwfix.

In theory you are supposed to erect it first and then pull the cables through, but...

BTW - have you done your voltage drop calcs - looks like a long run for a cooker circuit...

 

[dingbat]

BTW - have you done your voltage drop calcs - looks like a long run for a cooker circuit...

Most cookers run happily on a 32A breaker in 6 sq mm cable. A length of 9m was mentioned, but you could run it up to 39m from a 32A type B MCB.

 

[phykell]

Good call on the overflow waste pipe. I can probably fit that without having to fix wood to the wall first as well!

I've done a check here:

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

I guessed at 3kW for the oven (a single), and 6kW for the hob, that's 1.2kW for two small rings and 1.8kW for two large rings. Combined total is 9kW which if it's in trunking, for 8 metres, requires 10mm cable (load is 39A). I think I'll go with the 10mm cable anyway. I take it that the terminals in a typical 45A cooker switch will happily accept two 10mm conductors?

[edit] of course I can just use 6mm from the CCU to the hob and 2.5mm to the oven!

 

[ban-all-sheds]

I know there is all that stuff about short runs of cable, and visibility etc, but I still don't like the idea of 2.5mm² cable on a 40A breaker....

Re the plastic pipe - you'll need to avoid bends, as they are too tight for 10mm², unless you use singles.