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Posted By Topic: The differences between UK and NZ electrics

RAFB24
Mar 26 2018 10:53

Hi
I'm an ex UK approved sparky and I've been over here for just over 10 years. I'm tired of going in to my local Electrical trade shop and getting looked down at because I'm not a NZ certified Sparky, especially when I ask for something that is called on thing in the UK and another over here.
I've no interest in getting back in to the trade as I"m enjoying the easier life, but I do want to do my own electrics (obviously getting it signed off at the end).
What I want to know is what are the differences between some things here.

What do you call capping over here and do you use it. In the UK it is U shaped plastic or metal enclosure for cables that are run in chases in the wall. The nearest I can find is a Marley product called Top Hat trunking. Is it called something else here or do you/we just use conduit for this kind of thing. Basically I'm putting some sockets in to my garage but before I re-Gib the walls I want to run the cables in behind the Jib on the blockwork walls.

Another question I have, is what is the official stance over here for using Ring Mains for sockets over Radial circuits?

Thanks
Gary
   

Satobsat
Mar 26 2018 11:30

Find a different supplier if they are being arrogant and condescending towards you. They are probably charging you too much anyway if that is their attitude. You might want to have a look at the site I have linked below as an alternative?

I am an expat that trained as an electrician here in NZ. I have heard trunking being called capping here in NZ by Kiwis before now.

The only rings I have ever run are for actives and neutrals between RCDs in switchboards. There is new ruling coming in about the looping method of these rings being such that the ring will not be open circuit and remain continuous if a device is removed from that ring. I presume it is to prevent open neutrals which would prevent RCDs operating and also to prevent the overloading of conductors.

https://www.kiwisparks.co.nz/
   

RAFB24
Mar 26 2018 11:51

Thanks for that, much appreciated.
Yeah I think I'll take your advice, they stung me for cable as well. I bought a roll of 2.5 T&E and it cost me $400 they showed me the invoice and said I had been given 65% off.
When I said I saw the same stuff in Bunnings for $160 they pointed to some warning poster about cheap imported knockoff cable and intimated that it was what Bunnings were selling.
I paid it and walked out vowing not to go back again. I've actually found a good supplier of sockets and stuff on Trademe. but will check your link out as well.
So what's the deal with Ring Mains, I want to use it in my garage conversion purely for the number of sockets I'm putting in to the main cave.
   

Satobsat
Mar 26 2018 12:18

I have known reputable suppliers sell TPS that was not compliant so who are they to point fingers?

Ring mains in installation wiring seems to be a UK thing. Never come across them in NZ except in switchboards as I already mentioned.
If you are going to run a plug circuit as a ring main what conductor size are you going to use? Table 3.3 of AS/NZS 3000:2007 stipulates that the minimum cross sectional area for conductors supplying socket outlets is 2.5mm^2.
If there is thermal insulation in the walls this may need to be increased due to de-rating factors if you have a lot of appliances you are going to be using.

Running lighter cable in a ring main runs the risk of overloading conductors should there be an open circuit situation somewhere in the loop.

Ring main circuits were not taught here in NZ when I did my apprenticeship.

Why not just run two radial circuits in the correct size cable instead? It would be easier and cheaper. Plus saves the next electrician a head ache trying to figure out what you have done, should it ever require any work done on it.

Will you be getting the work inspected when complete? An inspector might not like the fact that you have run a ring main causing you more work to correct it.
   

mowgli
Mar 26 2018 12:49

RAFB24 before you install any cables find and make acquaintance with a friendly electrical inspector. An inspector is the only one who will be able to certify your work if you don't have a NZ practising licence. Given your experience there shouldn't be a problem if you organise it up front. However, if you present it as a fait accompli you will in all likelihood meet resistance.
   

dbuckley
Mar 26 2018 13:49

Never seen a ringmain used in NZ the same way they are in UK. In fact, never seen them used anywhere outside of the UK.

The funny thing is you almost could have a UK style ringmain in NZ, the killer being 3.4.3(a), minimum conductor size in parallel 4mm. Do it with 4mm, I think it would be OK in regulatory terms, but not cost effective.


   

AlecK
Mar 26 2018 14:01

The submains in army HQ Dunedin were (1980's run as ring, with several DBs fed by the ring.

   

dbuckley
Mar 26 2018 14:11

That was a distribution ring?

I've seen them in the UK, in Victorian mental institutions, that were sort-of circular; there was a 400V ring joining many large distribution boards, and an 11KV ring with ring switches, and transformers at intervals between the two rings. I always considered it a neat way to get a couple of MW of power around a very large site without lots of voltage drop problems.
   

SaintAlan
Mar 26 2018 15:57

Yes I only encountered domestic ring mains in UK, but am told they are used in Singapore also.
The idea makes sense for cutting volt drops in a large building but the big difference with the UK system is having fused 13A plugs. The fuses are meant to be appropriate sizes for each appliance.
   

AlecK
Mar 26 2018 17:00

was 400 V, in pyro,
Presumably done for redundancy.
Warships use similar principle, to allow flexibility in getting things going again after damage
   

dbuckley
Mar 26 2018 23:13

SaintAlan notes

> ... but the big difference with the UK system is having fused
> 13A plugs. The fuses are meant to be appropriate sizes for each appliance.

This is one of those interesting differences between UK and NZ practice; here the thing connected to the plug is not permitted to draw more current than the plug is rated for, 2.5.3.4(b)(ii), thus there is never a need for a fuse in the plug to protest against overload.

The minimum conductor size of a flexible cable is 0.75mm, table 3.3, and there is some data somewhere that says a short across such a cable will open the breaker sufficiently quickly that the 0.75mm cable will survive undamaged.

Thus, unlike many countries, there is no specific rule that says what the maximum size MCB that can be behind a 10A socket is, as long as the wiring is protected against overcurrent.

I'm sure there is a rule you cant have an undersized breaker feeding a 10A socket, but I cant find it.
   

Andrew
Mar 27 2018 12:47

I don't think the rule exists (though I think it used to). You do have to design to avoid nuisance tripping, but if you've got a socket-outlet that's for a dedicated purpose (e.g. lighting) rather than a general purpose outlet, you can be confident of the load on it and size the breaker accordingly.
   

mowgli
Mar 27 2018 14:22

dbuckley I think you might be refering to table C8 which suggests you can't put a 10A socket on a circuit less than 2.5mm or MCB less than 13A. That section is informative.

Table 3.3 is where the 2.5mm limit comes from, however, the exception allows smaller provided you consider VD, current capacity and connections.

1.7.1 requires that the installation should operate reliably under normal conditions. So a GPO on a small MCB would require marking to indicate the reduced maximum load capacity.