Domestic Conduit / Cabling Questions

[Citroënbender]

Referring to this simple diagram, not to scale. Meter box is the lower right:

I’m still waiting for the sparky to come!

These new circuits are spec’d as 6mm, 32A. While I’m waiting either for old mate or someone else more motivated, thought I’d run conduit and pull cables so the job is reduced to checking and termination.

Q1: Do circuits of this amperage require conduit along their entire length - or only when breaching an exterior wall, running underground or otherwise exposed/unprotected?

Q2: The longer run, I have the options of either ceiling cavity (thence wall drop) or subfloor routing, which is recommended? I know that ceilings typically carry more fire risk and cabling is sometimes derated in them.

Q3: Subfloor - the short leg - do I have to follow the run of bearers and joists, or can I take the most direct route (as sketched)? I realise this situation / possibility is impacted by any conduit requirements.

[jstanovic]

Amperage doesn't affect conduit/no conduit. Where it is installed is what's important.
Cables need to be "mechanically protected" in "accessible" areas. Accessible roofspace/underfloor is >600mm.
Mechanical protection also needed up to 2.5m above floor level in gerneral access areas (haven't got access to my rulebook on that one but it's around that).
Attaching a cable to a roof joist/rafter with a suitable clips to prevent sag is classified as mechanical protection, same as under floor.
If there is enough room I would keep the cable under the house rather than into the roof.
6mm cable won't necessarily be on a 32A circuit breaker, run distance/derating factors will determine that. Generally in a domestic situation a 32A circuit breaker on 6mm cable will past testing requirements (including volt drop and loop impedance) up to about 30m, but there are many online calculators to determine that. AS3008 has all the derating factors.
If it was in conduit then you can run it on the angle as shown. Bare cable, no.
If the cable is run is concealed (eg in a wall), needs RCD protection unless it is 50mm away from the finished surface.


If I was you I would conduit it all under the house, that way the sparky can visually inspect it. I've had people run cables for me in roof spaces, never has it turned out well and I have had to redo parts of it. My favourite was the AC circuit someone ran, from one corner of the roof straight to the opposite corner, over all the data cables, AC ducts, plumbing etc. Took me longer to undo it all and redo it properly than doing in from scratch.

[Citroënbender]

Thanks, very helpful. I should have added the run lengths, one is about 5-6m diagonal while the other about 24m to the shed’s sub board. A lot of what I’ve read about derating was from UK sites and their specs are obviously a bit different.

Underfloor access height varies from ~900 to barely 200 but I will dig clearance for a human torso when doing, if I have to. Life might suck for half a day, but then it’s done right.

[zilo]

Originally Posted by jstanovic

Amperage doesn't affect conduit/no conduit. .

What are you suggesting here?

[zilo]

I would just run orange circular cable, I think you can even get a direct bury version?

[Citroënbender]

You’re thinking of direct burial XLPE?

I’ve already got orange conduit buried under concrete between house and shed, 32mm dia x 600 deep, draw cord all ready, no warning tape though. It turns up to a weatherproof junction box mounted to the house wall at floor level.

If I re-mount the junction box 150mm lower, I can use 25mm HD corrugated conduit with a gland, entering at the rear of the box and punching straight through the wall just under the joist. Conduit under the house can mostly be run quite readily - just a few single skin sub walls to bore through.

[zilo]

Originally Posted by Citroënbender

You’re thinking of direct burial XLPE?

I’ve already got orange conduit buried under concrete between house and shed, 32mm dia x 600 deep, draw cord all ready, no warning tape though. It turns up to a weatherproof junction box mounted to the house wall at floor level.

If I re-mount the junction box 150mm lower, I can use 25mm HD corrugated conduit with a gland, entering at the rear of the box and punching straight through the wall just under the joist. Conduit under the house can mostly be run quite readily - just a few single skin sub walls to bore through.

I would draw it through your conduit and use it point to point anyway...its good shi te.

I did a 500m run at my place..

https://www.electracables.com.au/0-6-1kv

[Itsme]

Originally Posted by zilo

I would draw it through your conduit and use it point to point anyway...its good shi te.

I did a 500m run at my place..

https://www.electracables.com.au/0-6-1kv

Hope you bumped your cable size up for a 500 metre run as that would give you a decent voltage drop.

[zilo]

Originally Posted by Itsme

Hope you bumped your cable size up for a 500 metre run as that would give you a decent voltage drop.

16mm.

[.:4:.]

Granted this is from the 2007 as 3000, but the maths remains the same as towards voltage drop.

[.:4:.]

This a my in general hot tip. When it comes to Australian standards they're not cheap. However, if you know a person enrolled at TAFE, they can take a usb stick to the library and download any standard they like for free. Regardless of what course they are doing. There is a 3 day expiry on the pdf. So within that 3 days, take the usb to officeworks get it printed doublesided and bound and it'll save a fortune.

[.:4:.]

Also, when you attach your cable to the draw wire, attach a second draw wire with the cable just for future if needed. Nobody likes the selfish guy who leaves no draw wire.
Once your cable is into under the house, if the conduit is away from potential ingress of water, you can just cable clip it to the beams under the house. No further conduiting required. Suitably fixed away from mechanical damage.

[Citroënbender]

That’s a bit forward-thinking and considerate to leave a draw cord. Doesn’t happen often in Sydney. Around here it’s “rush the job, realise it’s wrong, lots of shouting, smash it up and try again, more shouting, try to push it through a dodgy certifier then call the gweilo to fix when it can’t be signed off as built”…

Re-measured my longest proposed run including drops, it’s 22m or slightly less to the intended sub-board location in my shed. Biggest loads on that right now are a large single phase compressor, old fridge and half a dozen twin 1200mm fluoros (normally only two or three are used). Presently supplied by unprotected 4.5mm through the roof cavity thence aerial conduit, it dims the lights when the compressor starts.

[Itsme]

Originally Posted by .:4:.

Also, when you attach your cable to the draw wire, attach a second draw wire with the cable just for future if needed. Nobody likes the selfish guy who leaves no draw wire.
Once your cable is into under the house, if the conduit is away from potential ingress of water, you can just cable clip it to the beams under the house. No further conduiting required. Suitably fixed away from mechanical damage.

I always use to rub talcum powder on cables when pulling cable through an existing conduit with cables as I found it reduces friction and burn to existing cables, just an old trick I learned when I use to do commercial refrigeration wiring when I was last in the trade.

[.:4:.]

Originally Posted by Itsme

I always use to rub talcum powder on cables when pulling cable through an existing conduit with cables as I found it reduces friction and burn to existing cables, just an old trick I learned when I use to do commercial refrigeration wiring when I was last in the trade.

I always used cable lube, or at a pinch without that, pump bottle hand soap.

[.:4:.]

As for always leaving a draw wire behind. Yes its for the next bloke who will probably be an A hole and not do the same, but if you happen to do the addition to the same job and your draw wire is there, man, life is so much easier when you make it less difficult for yourself.