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Posted By Topic: 2x 2.5 T+E Used For 3Phase

mk268
Jan 25 2019 07:38

There’s a new installation where the heat pump contractor has run 2x 2.5T+E circuits to each 3 phase heat pump. Is this considering as conductors in parallel or not? As I know you can’t parallel 2.5.
Also the black is marked as a phase with one piece of blue tape each end. Does it have to be sleeves phase colour the entire stripped back length?
Thanks
   

pluto
Jan 25 2019 08:05

AS/NZS 3000:2007 Clause 3.8.2 has the answers you need.
   

DougP
Jan 25 2019 08:18

No they aren't conductors in parallel, because there's none of the conductors in parallel.

The only thing they might have done, is used both of the earth conductors. Personally, I would do that as well, as they are not carrying current under normal conditions. And, if they only connected one of the earth conductors as an earth, they would have to protect the unused conductor against induced voltage anyway.
1.5.11.1(b)
1.5.11.4

As for the sleeving, some might say that tape is not suitable for identification. Not best practice anyway.

And for sleeving the entire length of the primary insulation, 3.8.2 doesn't mention that as a requirement, and it actually says "each termination", which if you took it literally, would mean right at the termination.

In any case, you seemed to have figured out what's going on with the circuits, so up to this point, the identification is working as required.
   

AlecK
Jan 25 2019 09:29

Without a pic, hard to know what "one piece of blue tape each end" looks like. I agree with DougP that the fundamental rule for ID [3.8.1, para 1] has probably been complied with - but in my view just barely.

Seems they have chosen to use colour as the means of ID (there's no suggestion that any other method of ID has been used). Therefore the entire system as per Table 3.4 becomes mandatory, NOT just some of it. Using a conductor that has black insulation as an active is not permitted by the Table; but 3.8.2(a) allows "sleeving or other means" to alter the colour, but it has to result in the colour conforming to the Table; ie it must be clearly & obviously NOT black. Hard to see how "one piece of blue tape" can comply with that.

Previous edition banned use of tape; it allowed only heat shrink sleeving, fixed sleeving, or elastic sleeving applied by applicator; andfd the colour ID had to be colourfast, permanent, non-conducting, compatible with cable insulation, and suitable for the location". I for one would like to see that ban reinstated


   

DougP
Jan 25 2019 12:06

I'd be interested in hearing your opinion on both earth conductors being used Alec.

This question has come up a few times, mainly on Australian forums.. with 3ph A/C being common over there.
   

AlecK
Jan 25 2019 12:46

I think you're on the money on that one.
Earthing requirements can be met using only one PEC.
But dis-used conductors of "associated with" connected conductors must be safely terminated. One method of safely terminating is connecting to earth; but that isn't "in same manner as is required for live conductors". But then if both PECs are connected to earth at both ends; ie parallel; they are not "unused".

Like any requirement, the limits on connecting in parallel have to be read in context.
3.4.3 - where the 4 mm2 minimum is imposed - is about is part of 3.4 current carrying capacity (as in load current, not fault current); and since the PECs don't carry load current the rule can't apply.
3.6.3 is about voltage drop in a circuit, so again not relevant to PECs.

And certainly having them in parallel cannot adversely affect their function as PECs.

That said; using 2 x 2C&E cables for a 3-phase circuit is far from good practice. Should use a 3C&E for the job or $C&E if needing a N. With 2 cables, there's a risk of someone not realising that it's a 3-phase circuit, and the 2C&E they are disconnecting includes the PEC, and/or the N, for another cable that hasn't yet been isolated.
   

Someone
Jan 25 2019 17:44

Assume you meant to write 4C&E not $C&E.

Most (all?) 3ph AC units need a neutral. Lots of controls in there.

I have seen a 3C+E plus separate SDI neutral used in a lot of older cases (though not aircon).

But circular 4C+E is now readily available, so that should really be the preferred option.