Appropriate size cable for GPO and lighting circuits?

[Pete F]

G'day guys, I need to run some wires for both a standard 10A GPO circuit and also domestic lighting circuits and will need to order the cable. Can anybody who's familiar with the code advise what is the appropriate wire size for both these types of applications. Install is in NSW, domestic if that makes any difference. It's been too long since I worked in this field so have no idea what the present code demands.

Thanks.

[BRADFORD]

AS3000 will answer your questions.
I would advise that you don't attempt this work if you are not familiar with the Standard.

[Pete F]

AS3000 will answer your questions.
I would advise that you don't attempt this work if you are not familiar with the Standard.

Thanks. :rolleyes:

Mate this is about as easy as it gets, I just need to shift some points and lights. I used to work in the field, but that was well over 20 years ago, and simply want to ensure anything run meets current code. I'm not asking for somebody to explain brain surgery to me, just what are the minimum wire sizes!

[chrisp]

Such questions are a little sensitive on this forum... :rolleyes:

Have a search of the forum - there has been a table posted sometime ago. Also, search some posts by a member with the user name of "Master Splinter" - his signature has a link to some useful information.

Essentially, not that much has changed with regards to cable sizes - except - "completely surrounded by insulation" can happen more often. You'll need to be careful of the CB rating if running the cable in insulation.

[Pete F]

Cheers Chris, yeah I can understand the sensitivity ... to a point. Pretend I'm in NZ then :wink: Besides, it's not like somebody is popping up and asking "how do I wire a "Power Point"?" It was a specific question relating to wire size, not exactly a punter question I would have thought.

A-n-y-w-a-y ... I was presuming the lighting was protected by a 8A breakers, but in fact they're 16A, so good thing I looked! The GPOs are protected by 20A RCDs, so I'm thinking of 2.5 mm for both but will hunt around for that table. I'm pretty sure it will be free air but might presume it will be insulated just in case. I'm guessing type of insulation isn't important? It's in a garage/workshop so some may however go through conduit. Given the runs aren't long it's no biggie if I over spec. The wiring in this place is a mess, the majority of the house is on one circuit, and to top it off somebody stuck a nail through N - E. Of course it was like that for years and nobody knew ... right up until we put the RCDs in :doh: The sparkie and I spent a few hours trying to find it, he gave up and it took me the whole of the next day to track it down. I don't miss this :U

[Master Splinter]

Actually, AS/NZS3018 is even handier for domestic stuff, as it's the wiring rules less all the industrial 'calculation of demand for your aluminium smelter' nonsense.

Generally, it's 1.0mm for lights, 2.5mm for standard power outlets (those are the 'shall not be less than' limits). Circuit breakers for these should be 10 and 16 amps respectively - that assumes that the wire is partially surrounded by thermal insulation. If it's in a roof space that's uninsulated I think you have to assume that it will be insulated one day and rate the cables accordingly.

The doc linked in my sig will also help with the fiddly requirements for domestic installations as it is the handyman and DIY-electrical and home wiring document issued by the NZ electrical regulator.

(AS/NZS3018 and all the other info is in a torrent, too - 'aus electrical' should find it on your favourite torrent site)

[Pete F]

Actually, AS/NZS3018 is even handier for domestic stuff, as it's the wiring rules less all the industrial 'calculation of demand for your aluminium smelter' nonsense.

Generally, it's 1.0mm for lights, 2.5mm for standard power outlets (those are the 'shall not be less than' limits). Circuit breakers for these should be 10 and 16 amps respectively - that assumes that the wire is partially surrounded by thermal insulation. If it's in a roof space that's uninsulated I think you have to assume that it will be insulated one day and rate the cables accordingly.

The doc linked in my sig will also help with the fiddly requirements for domestic installations as it is the handyman and DIY-electrical and home wiring document issued by the NZ electrical regulator.

(AS/NZS3018 and all the other info is in a torrent, too - 'aus electrical' should find it on your favourite torrent site)

Nice thanks for that, precisely what I was looking for. Does the "code of practice" doc for NZ mirror pretty much precisely the same requirements as in Oz? I've just had a quick skim through so far and looks indeed like there's either changes or stuff that I didn't remember. A couple that come to mind was the requirement for isolation switches at water heaters/ovens, also the amount of space required around a wire when going through a stud, I don't recall that one.

I wonder why the lighting circuits here have 16A beakers? The RCDs installed are Clipsal RCBM220/30 which I thought was pretty standard. I got the RCDs installed as soon as I bought the place, however the sparky said he had also done other work here previously. The vendor gave me a list of who he had used so I got the same guys in as I figured they knew the house. However I'm now wondering why they'd use 16A MCBs??? To be honest I hadn't taken any notice until now, but come to think of it I'm pretty sure I saw 1 mm wiring for at least some of the lights. Again, I didn't really notice because it's pretty much what I expected to see.

[chrisp]

- that assumes that the wire is partially surrounded by thermal insulation. If it's in a roof space that's uninsulated I think you have to assume that it will be insulated one day and rate the cables accordingly.

Clip your cable run to a stud/joist in an (thermally) insulated cavity and it will be considered as "partially surrounded by insulation". Let it lie loose or unclipped and it'd be considered "completely surrounded by insulation". :wink:

[Pete F]

Cheers Chris. Generally I'd clip if I can, but not sure if I could guarantee a cavity. When I heard about the government's brainwave of free insulation I thought it such a monumentally stupid idea that it couldn't possibly last ... I couldn't sign up fast enough. The company was perfectly happy o install over my existing insulation so I basically have to wade through the stuff up there now :U

Any clues as to WHY these guys have put in 16A breakers in the lighting ccts? The whole idea of getting a currently licensed person in to do work I'm perfectly capable of doing myself is to make sure everything is legit and passes code. I'm going to be real pissed if I find out the work is dodgy. Also are the 20A RCD/MCBs pretty much standard issue? Again they were a little larger than I would have expected.

[chrisp]

However I'm now wondering why they'd use 16A MCBs??? To be honest I hadn't taken any notice until now, but come to think of it I'm pretty sure I saw 1 mm wiring for at least some of the lights.

If the cable is "partially surrounded by insulation", the CB should be no larger than 10A. If it is "fully surrounded, then the CB needs to be 7A or less. The above assumes V-75 or V-90 two-core (plus earth) cable. The 16A CB is too high for 1mm2 (except when the cable is buried)

[Pete F]

Looks like I have a bit of investigating to do. They were in here before I bought the place, but as mentioned I understand the same guys are doing the work now as previously. Quite WHY anyone would have such large MCBs in there is a mystery to me. What I have seen in the past is people chucking stuff on the lighting circuits, so now that has me a bit concerned.

Until now I haven't really given all this too much consideration. When we moved in the first thing I did was go around and test all the GPOs to make sure they were all wired correctly. When I had to track down the nail through the n - e I saw the house load wasn't shared too well. But other than that it's been one of those things I haven't really given much thought to. It's come about simply from the desire to shift a few things around but looks like it's a good thing it's come up.

[chrisp]

But other than that it's been one of those things I haven't really given much thought to. It's come about simply from the desire to shift a few things around but looks like it's a good thing it's come up.

I think it is good for everyone to understand the "whys" of electrical work if they are so inclined. The knowledge certainly helps the home owner understand what should (and shouldn't) be in their electrical installation.

Good luck with it.

[Pete F]

Yeah thanks Chris. I've been aware that a few things weren't quite right, but you know how it is, if it ain't truly broke ... don't look too hard.

Ok I guess I'm not exactly like the typical punter when it comes to this, but it still erks me that the unions have stitched this side of things up so absurdly in Oz. I'm the first person to say to somebody that if you don't know what you're doing don't touch electricity because it very often won't give you (or somebody you love) a second chance. Yet we have the situation here where, unlike many other 230v countries, the home owner isn't allowed to touch anything hardwired. Now some may say that's fair enough, but plug it in and you can go berserk, do what you like really. If it's so controlled, how is it that Joe Punter can walk into, not only somewhere like Bunnings, but K-Mart of all places, possibly even decent supermarkets and buy GPOs, light switches, and goodness knows what other electrical hardware. Of course nobody will tell them how to actually use them, "hire a licensed electrician" they say (who apparently shops for GPOs at K-mart). So Joe home owner invariably has a go anyway and goodness knows what happens. As I said, it was literally on the first morning of being in this house I went around and tested EVERY GPO because I simply don't trust previous home owners with my life or the lives of my family. I think it should be either one or the other; they should simply not be available except through trade style outlets. Alternatively if this sort of thing is going to be available through common retail outlets make sure the users have the required information to use it properly!

Sorry, rant over :q

[elkangorito]

I remember years ago when I was a lad, one had to produce an Amatuer Radio License in order to purchase an Amatuer Radio. This was not a legislated fact but some stores simply decided to do this.
I had an Amatuer Radio License but it was not a 'full' license & I wished to purchase some equipment that required a 'full' Amatuer Radio license. What did I do? I simply circumvented the usual process & purchased my equipment via 2nd hand dealers.

These days, anyone can buy an Amatuer Radio without restriction. The restriction happens when one decides to use such a thing.

I can see no problem whatsoever selling electrical items to all & sundry. The problem arises when uneducated people take matters into their own hands. If the Australian government had any brains, they would adopt the NZ ideal, which is 'education', since so many people seem determined to DIY anyway.

[Master Splinter]

Isolation switches are a weird one - we don't have a requirement for visible isolation switches for cooktops (as specified in AS3000 - 4.7.1) here in the ACT (or if we do, it's never been enforced) like they seem to have in some states (we just have the oven and water heater identified in the switchboard so it can be turned off there).

I haven't noticed any particular differences across Aus/NZ, but this is based on looking at Australian houses under construction, so I'm looking at what is done, not what should be done but is ignored by all and sundry.

The only difference that I am aware of between Australia/NZ is that NZ specifies slightly lower temperature values for the standard ambient temperature when this is to be used in calculations, and different size earth stakes. In AS/NZS3000, there's a little box with either A or NZ in it indicating that there's a difference.

You can actually chuck a standard GPO onto a lighting circuit, as long as it's located 2300mm off the floor and the doohicky to be connected to it draws less than 150 watts (both figures from memory so don't quote them).

[NigeC]

many factors are to be considered by a qualified person.
NSW doesn't matter, AS3000 is Australia wide.
It is strange for a light circuit to be on 16A MCB
It is strange for a power circuit to be run straight of a RCD

[Pete F]

Nige, I agree with your "strange" observation re the lights. Hopefully I'll be able to spend the next couple of days crawling around finding precisely what's going where and why. I could understand if one of them was higher if a previous owner had tried to bodge something to hang a patio heater off a light cct or some similar bizarre carry-on, but not both???

I was perplexed by your RCD comment however. They're standard RCD/MCBs

[NigeC]

Normally the RCD/MCB feeds MCB's, so one RCD can supply more than one final sub circuit, and the sub circuits can be independently switched.

[applied]

Some companys only install rcbmbd combos when running every circuit this prevents existing faults being attributed to there work the one I work for being one or more than one tripping due to fault situations.
Customer pays there's no point doing it cheap the markups pay for wadges, vans, time at wholesalers, non paying customers and timewasters. I know it's barely related just putting it out there

[Pete F]

Some companys only install rcbmbd combos when running every circuit this prevents existing faults being attributed to there work the one I work for being one or more than one tripping due to fault situations.
Customer pays there's no point doing it cheap the markups pay for wadges, vans, time at wholesalers, non paying customers and timewasters. I know it's barely related just putting it out there

Yeah that's what they did here and also what I've seen on other boards so I just presumed that's the way everyone was doing it these days. Apart from the cost the other thing is they're double width and I'm rapidly running out of room :( On the plus side and RCD tripping doesn't take out the lot, a big plus to me. I have a lathe running on a VFD and anticipate all sorts of dramas once I try running that with an RCD. We'll see.

[NigeC]

Agreed, there is a number of way to do it, if it is a smaller board I will go for the single width RCBO, if I have 20 poles I will go for the double width RCD which feeds MCB's. So much cheaper

[elkangorito]

Any clues as to WHY these guys have put in 16A breakers in the lighting ccts? The whole idea of getting a currently licensed person in to do work I'm perfectly capable of doing myself is to make sure everything is legit and passes code. I'm going to be real pissed if I find out the work is dodgy. Also are the 20A RCD/MCBs pretty much standard issue? Again they were a little larger than I would have expected.

The reason why 16amp MCB's have been used for the lighting circuits is probably because the cable supplying these circuits is 1.5mm squared copper cable (TPS). This allows the homeowner some latitude when it comes to the size of lamps used with the circuit.

'General practice' is to use 1.5mm squared cable for the lighting supply circuit...not 1mm squared cable. 1mm squared cable is generally used as 'switch wire'.

[Pete F]

I think you're right. I started going through some stuff today and noticed both power and lighting was heavier than typical, but it was late and I couldn't see exactly what it was. However what I'm concerned about it that while MOST may be that gauge, some additional work may not be. I presume it would be the smallest gauge on that breaker that would establish the size required? Anyway I think I'll change them to 10A. We use mainly low energy lighting now, with the exception of some outside floods my wife seems to like illuminating the suburb with. 4 of them alone are 800W IIRC! However there's still a good margin.

[NigeC]

A 1mm switch wire would derate the 1.5mm cable to 1mm anyway.