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Posted By Topic: sleeving NS Cable

ppaw1965
Jan 24 2014 23:18

Some help here please. I was told a 3 or 4 years back that the screen on a NS cable cannot be used as an earth. Is this still the case or not as I can find no prohibition in the regs or the rules (ASNZS 3000)? 3.8.3.1.(b) seems to say I can but 5.3.2.4 sort of says I can\'t as the screen isn\'t braided or am I reading this wrong? perhaps only the bit that is exposed needs to be sleeved.
The other option is to use the screen as the Neutral and use one of the other conductors as the earth and sleeve to 3.8.2.
Thanks for any help.

   

pluto
Jan 25 2014 08:36

ppaw1965 Jan 24 2014 23:18

The Wiring Rules (3000) requires that the screen of a neutral screen cable to be an earthed conductor, which in practical terms means that it must be EITHER the neutral conductor, OR. the earth conductor.

The use of a core of the neutral screen cable as an earth conductor means that the earth core can not be continuously identified as the earth conductor. refer 3000 clause 3.8.2.

Thank you for pointing out a problem (missing cross reference) in clause 5.3.2.4 in respect to neutral screen cables. I will add to this point in amendment 3 of 3000 currently under preparation.

This is brought about in 3000 because in Australia neutral screen cables are not used as much as they are in NZ for sub mains and final sub circuits and has been overlooked when doing the detailed checking on publication and the 2 amendments.

Use clause 3.8.3.1 as the authority to use the screen as the earth conductor in a neutral screen cable.
   

AlecK
Jan 25 2014 09:27

The screen of a N/S cable has insulation in the form of the cable sheath.
So as long as you insulate the tails at each end - ie replace the insulation you have removed - no exception under 5.3.2.4 is needed.

(errors are sometimes made, but this isn\'t one of them)

3.8.3.1 just means the main part of the screen doesn\'t need to have colour ID provided the tails are correctly identified (green/yellow).

   

ppaw1965
Jan 25 2014 11:03

Thanks for clarifying that. Means we can use the screen as the earth.
Pluto , In ref to 3.8.2. The understanding I\'ve had of this clause is that it is acceptable to sleeve the ends of an active conductor as an earth (subsection (c)).
The only exclusion seem to be the last couple of paragraphs, first is A1 which a single core cable needs to be sleeved along the entire length if used as an Earth. And last paragraph prohibits an earth conductor to be used as anything other than an earth.
The reason I was given was if you cut into a multicore cable and find an earth you expect it to be dead. If you find an active conductor you will always treat it as live.
I know the subsections of 3.8.2 seem hard to follow as I sat down with another sparky and Inspector who were working as teaching tutors and we went over this quite a few times before it made sense. This clause sounds like it was left over from the previous rule book which was all written in legal mumbo jumbo.

Cheers, Thanks again
   

ppaw1965
Jan 25 2014 11:16

c
   

AlecK
Jan 25 2014 12:01

Yes, it is acceptable to sleeve an active of a multicore cable as an earth.

The change in A1 for colour ID of single-core earths was to add the word continuously. Previously marking at intervals was permitted.. but lazy sparkies made the intervals longer and longer until in some cases the marking was ineffective.

The clause is not really that hard.
I agree it needs people to take it carefully, each paragraph by itself.

a) says you can make a N into an A (but you can\'t make a E into an A).
b) says you can make anything except an E into an N
c) says you can make anything that isn\'t already an E into an E.
   

ppaw1965
Jan 25 2014 12:16

Don\'t know what happened to my last post. Down to dial up speed as kids used all the download.
Instead of c was meant to say that found an old copy of ASNZS3000-2000. In 3.8.3 sleeving was required on full length in Aussie but only ends in NZ for multicore cables.
Now in current book is as AlecK says.
By the way your explanation sounds easier. Perhaps you should write the rules instead.
Thanks
   

ppaw1965
Jan 29 2014 11:32

Just one more thing, Is there somewhere in the rules where it is prohibited to use the screen of a NS cable as an active? Other than a really bad idea and whoever tried it should be shot.

Your comment Pluto \"The Wiring Rules (3000) requires that the screen of a neutral screen cable to be an earthed conductor, which in practical terms means that it must be EITHER the neutral conductor, OR. the earth conductor.\"

I just did a search right through ASNZS3000 and couldn\'t find anything other than referance to \"Suitable screen used as an earthing conductor\".

I would hate some silly bugga wanting to interpret the rules by saying \"sleeving N as an A\".
   

AlecK
Jan 29 2014 13:37

While I appreciate the compliment, my (over)simplified re-wording of 3.8.2 is not strictly accurate.
The wording in the clause is accurate.


We can sleeve a conductor that has blue or black insulation as an active.
But we can\'t sleeve the screen of a N/S as an active, because (on the bit we would be sleeving) it doesn\'t have blue or black insulation.


An example of why it\'s hard to write a rule that says exactly what you want it to say, and can\'t be twisted into meaning something else, and copes with every possible situation (not just the most common ones); all without wasting words.




   

ppaw1965
Jan 29 2014 13:49

Thanks for that clarification AlecK.
Yes I would hate every possible scenario to be mentioned. I would hope sparkies would continue to use common sense so we don\'t end up with rule books looking like the Encyclopedia Britanica.