2009-Apr-3 - Wooroloo - Electrical #2
Scroll right down to the bottom of the page to view all the graphics.

The first image is a floor plan for the undercroft indicating the positions of all the photographs

If you click on an image you will be shown a larger version - you can enlarge 3 times - so just keep clicking if you need to see more detail.

The main issue here for me to resolve is the physical boring of holes through the steel structure.

I am not sure how many holes can be made through a member without weakening it too much - nor who I can ask about this.

There is a 25 mm access hole at the top of every stud (just under the top plate) - this will be useful for a proportion of the required cable runs. I will have to go up through the top plate whenever I encounter any of the 75 x 75 mm columns.

How many 2.5 sq mm cables could I fit through one of these (with its grommet) ?

At the moment, all I have is some NZ standards, written for the householder, that I downloaded from the internet.

It says that any cable must be at least 50mm from the cladding surface - which is a problem here seeing that the stud frame is only 75mm thick. Does this regulation apply in Western Australia ?

If so, do I get around it by running conduit throught these holes ?

#1 : Above existing temporary power board.

I'm assuming that I can get a switch cabinet that will fit between 450mm centres and sit right in to the wall cavity so that the access panel intrudes a minimum in to the garage space.

At this stage I am thinking we will eventually send a 16 sq mm riser through the top plate to a subboard for the main level / loft. The subboard would probably go in a pantry area directly above.

The main reason I want to do this is because I think the top plate would start to look like Swiss cheese by the time the cabling for the entire house had passed through this area.

This picture shows 3 different positions for cable runs:

(a) through the 25 mm holes in the studs immediately under the top plate, running along the length of the wall

(b) up through the top plate and then running parallel to the purlins - to cross to the other side of the room. (they would hang off the floorboards)

C) through holes (to be created) in the studs immediately above the waist height noggings - mainly useful for electrical outlets around the room (problem when 75 x 75 mm columns encountered)

#2 : Cable runs to the opposite side of the room.

I will need to bore through two sets of Standard Bracing (the cross pieces that stop the z purlins rotating) but as these are not weight bearing, this is not a problem.

The holes to descend down through the top plate could affect their integrity - so need some advice on this.

When we met on site, we were talking about running back to the large central beam, along this beam and then back out to the wall.

Upon reflection, I'm trying to see how this would help me, as the ceiling will be clad and we would end up with cable runs hanging below the ceiling.

#3 : Descending through a top plate, additional holes.

This is the same view as #2 but just more in to the upper corner of the ceiling on the far side of the room.

I need to find out the best position for descending through a top plate - in the middle between two load bearing points, or as close as possible over the top of a supporting stud ?

This picture also shows some additional cable paths that could be bored through the Z purlins.

Directly over the top of the stud frame would be the safest, I'm betting, but would be very hard work getting a drill in to that space and drilling through two layers of plate (the z purlin and a pressed sheet right angle bracket).

Again I need to find out the minimum spacing between consecutive holes along a z purlin that can be allowed without degrading the structural integrity.

#4 : Navigating around a column.

Shows typically the cabling to work around a column.

Would apply equally to a cable run passing along just above the waist height noggings

#5 : Across top of garage / laundry wall.

This is the wall that divides the garage from the laundry area.

This looks like an easy area to work in - could run quite a large cable bundle through here with descenders reticulating off for various wall sockets (to both sides of the wall) and running on to the bathroom.

Is there anything to prevent the cable bundle just resting on the lower surface of the z purlin?

Is there any restriction of the size of the cable bundle and the proximity of any circuits ?


Undercroft plan / photograph locations


25 mm access hole at top of every stud


#1 Above current Distribution Box


#2 Cable runs to opposite side of room


#3 Descending through a plate, additional holes


#4 Navigating around a column


#5 Across top of garage / laundry wall