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Posted By Topic: 1.5 for lights AND Fully Surrounded?

May 28 2012 18:04

Hi all

Do we now have to rate our cables in a domestic situation , for the rating completly sourrounded by thermal insulation , as this maybe installed at a later date???

That would mean that 2.5 is only good on a 16A MCB , not 20 , and 1.5 on C10 , and 1mm2 on C6?

Got job on atm were the install in a steel frame room , and the cables are fully surrounded by thermal ins , and there are 11 doubble 58W flouros on 3 sep switchs ,at the door, and 3 bulkheads , and a security light.....Have wired in 1.5 and plan to put on a C10A MCB.

There are 2 doubble flouros in sewing room , 2 doubble flouros in workshop , and 1 doubble 58Watter in the garage....have wired these in 1.0mm2 , and will put on a C6A mcb.

Is this what the norm is now???? Using 1.5 on 10A mcbs , in situations where the cables are fully surrounded?

Ive used 1.0mm2 for the other 5 lights as the load current is quite small , but ive used 1.5mm2 for the rest due to the shear number of lights that are on the cct and the chance that they maybee all on together there would be a load current of 5.5Amps , thats excluding the outside lighting thats why im comfortable on the C10A MCB.

I know its a little more expensive to use 1.
5 , but in this situation this is what my gut feeling was to use.

Feedback appreciated ( p.s ill put my helmet on!!!! )


May 28 2012 18:23

Oh , and the sockets i wired in 2.5 on a 16A MCB , with exception of the garage/workshop where i installed a 4.0mm2 , for a little future proofing incase they get somehing grunty as you will have no acces into ceiling space.

Purhaps they may install a caravan outlet out there later on at some point also.

The Don
May 28 2012 18:27

Craig , I would say your right on the money with your assumption .


May 28 2012 18:34

So you would have used 1.5 too for the amount of lights in this situation?

Distance in bugger all , purhaps 12-15 tops.


May 28 2012 18:45

Short answer: \"No\"

You only have to allow for insulation being added later if there\'s none there now. Otherwise just deal with what\'s there now.

And if you\'re silly enough to thread your cables through the batts for more than 150 mm, then by all means de-rate for completely surrounded. I\'ll keep running mine along joists, or laid under insulation on the ceiling, or laid on top, or between wall lining and insulation; all of which = partially surrounded.

The Don
May 28 2012 18:57

Craig : based on the load you quoted and assuming it was possible all that light could potentially be on together , then yes it would be sensible to use 1.5 because you could well be over 6 Amps depending on what size lamps were fitted to the bulk heads etc . So if you were over six amps then as you already pointed out 1.0m would not comply if fully surrounded .
So did you make the right choice ? I would say yes . Do you not trust your own decision ? :)

May 28 2012 18:57

This situation , in my opinion is fully surrounded. i have roof , then the thinkness of the batts , then rondo battens and finally gib.

Got to remember the sun will beat down on it all day also. Basicly ALL my cables are run with batts all arround them.

\"You are defined by the choices you make. Good tradespeople will aim for the highest standards odf safety & workmanship; not what they think they can get away with\"???


The Don
May 28 2012 19:02

Alex, Craig did point out right at the begining that it was fully surrounded, so you would have to assume that he got that bit right in the first instance , in which case he would be correct with his calculations.
You would be correct if there was other options for the install

May 29 2012 08:04

True, The Don; but I wasn\'t saying his particular job wasn\'t; I was answering his opening question:

\"Do we now have to rate our cables in a domestic situation , for the rating completly sourrounded by thermal insulation , as this maybe installed at a later date???\"


Brian H
May 29 2012 09:40

Please dont add future proofing into our Calcs.Wonder why no one invented a little black box to turn all that wiring into Underfloor/in wall/in ceiling heating when not in use.?

Another Steve
May 29 2012 17:44

Just come back from my refresher course, or whatever it\'s called now

Head tutor there, at Weltec was telling the class to: carry on as always - ie 20A for 2.5mm etc, and that he was in talks with Standards NZ, and at this moment they are busy testing cables, and very shortly they are looking to \"re-rate\" cables as being able to hold more than currently rated for.

Don\'t shoot the messenger, but that\'s what he said....I tried to argue the logic, and he said...carry on as you were....

May 29 2012 19:00

Yes there is a chance that SOME cable ratings will be adjusted, because there is SOME evidence that they are conservative.
But it\'s NOT all of them, by a long shot.

At the same time it\'s likley that the max \"dive-through\" will be increased from 150 mm to perhaps 300 mm. But don\'t use that as a basis for working UNLESS / UNTIL IT HAPPENS.

Easy for a tutor to advise a course of action when s/he isn\'t the one signing the coC and being held to account for it.

So DO NOT \"carry on as before\". Instead, carry on according to the new rules.

Not shooting the messenger, Another Steve, but the tutor deserves to be shot with a ball of his own sh!t.

Brian H
May 29 2012 19:03

Messanger only gets shot upon delivering message,something to do with Subordination.In the Irish army,\"now,go tell them we out of bullets\"