Using the earth in control wiring as a control core?

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Using the earth in control wiring as a control core?

Post by JamieP »

Now this one seems to get a little complex and just based on previous comments and opinion I think it'll probably be a situational basis

Although probably not "good practice" (hate the term) would it be ok to use the earth core within a multicore control cable as a control core if needed?

I suppose it comes down to a number of factors, firstly is the control wiring installation wiring and does 3000 apply?

If it's simply sending signals (digital and analog inputs and outputs) then I'm assuming it's not

But what about if it also sends a 24V power supply for instruments that need an individual power supply?

Or does installation wiring stop at the load terminals of a transformer or power supply?

If it carries over and the ELV output is installion wiring then I would assume our color system would apply but that's only if we use color as the chosen form of identification and in most multicores, identification is done by numbering, although we still label each conductor regardless of numbers as to what they are, would this make the earth usable or at least usable if labeled to it's intended purpose rather than using it's colour?

Curious of opinions here and whether people think it's ok or not? It's not desirable for me but I have found situations with broken cores or similar that using the green/yellow core can save huge amounts of time and cost and I've had a number of mixed opinions from others
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Re: Using the earth in control wiring as a control core?

Post by AlecK »

Sorry, no simple answers in this area.

Traditionally Wiring Rules have been about the wiring that carries electrical energy from a point of supply (generally but not always from a distribution network or 'grid') to a point of consumption (an appliance).
Communications wiring (data, telecommunications, etc) has been treated as a different thing, almost unrelated.
There has always been a degree of crossover between these areas; and it's increasing.

Time was when control / monitoring of electrical equipment was entirely electrical; using relays, cam timers, pilot lights, meters, etc.
Mostly but not always at LV; but clearly within scope of Wiring Rules.
It's now much more common & monitoring to use comms cabling for control / monitoring functions; whether it be analogue or digital.

And rapidly coming is use of comms cabling to deliver electrical energy; eg 'power over ethernet'.
Which is already creating arguments about what rules apply - including who can do it.

You have correctly identified that your particular question hinges on whether or not the cabling in question is part of the "electrical installation" .
If it is, then Wiring rules apply; including the prohibition [ 1.7.2 & 3.8.1] on using conductors identified by colour as earthing conductors for other purposes. Note that this prohibition is universal; it applies regardless of whether colour is the chosen means of identifying conductor function.
If not part of the installation, ESRs do not require compliance with '3000"; and that means the prohibition does not apply. Easy to say, but unfortunately not so easy to decide.

Complicated by the fact that even if part of the installation, the conductor ID rules apply only to "installation wiring" and not to "equipment wiring"; even where the equipment is generally part of the installation.
There's a lot of discussion going on as to how the demarcation between "installation" and "equipment supplied by the installation" should be made in "3000"; and in particular clarifying the demarcation between "installation wiring" & "equipment wiring".
Not too hard for even quite complex assemblies that have a single poont of connection to the installation. Bit much harder for systems that are

Another complication is that while the definition of "electrical installation" in "3000"does not exclude appliances, the definition in our Act does - though what's excluded is "appliances" as defined not appliances as generally understood.

Also need to consider that even if not part of the installation at all, or not 'installation wiring" and not 'equipment wiring", there will still be Standards that apply to it. Though whether they are legally enforceable in the same way that compliance of installations with "3000" is enforceable via Regulations is another matter. Eg AS/NZS 4024: safety of machinery: electrical equipment of machines (which incidentally includes that same prohibition on use of C/Y conductors for anything other than earthing).

I'm part of the team working on these issues; but a personal opinion is all I can provide right now; based largely on the NZ definition of "electrical installation":
"... all fittings that form part of a system that is used to convey electricity to a point of consumption, or used to generate or store electricity" ; with exclusions for fittings of distribution & transmission lines (upstream of the POS), generation, and appliances.

If a cable is solely for communications / signal functions, then difficult to make a case that it's installation wiring.
But if it's used for supply of electrical energy to any appliance (consuming device) then it's probably part of the installation.

Prime example being the inter-connecting cable between the indoor & outdoor units of a split-system heat pump.
Typically this is a 3&E TPS, and serves dual purposes of carrying signals & delivering power.
Not supplied with the units by the manufacturer, so can't be seen as part of a single machine / appliance.
However used to be some where the interconnect did come (pre-terminated) as part of the kit, and was just plugged in at each end; so could then be argued it was all one appliance, and that plugging it in wasn't installing but merely assembling.

Being ELV makes a difference to who is permitted to do the installation work (PEW or not PEW); but makes no difference to the fact of it having to comply. Note the wording of ESR 59: "every low or extra-low voltage installation...".
The only reason the ELV wiring distributing energy around your car (or my boat) doesn't have to comply is they are excluded from ESRs by ESR 3.
So ELV wiring that "conveys electricity" (as against carrying a signal only) is part of the installation.
That includes ELV supplies not only for lights but also for control systems.

It's often tempting to bend the rules to avoid having to comply.
But cost & difficulty should only be factors in choice of how to comply, not in whether to comply.
So unless you can clearly show that the cable concerned serves absolutely no "conveyance of electricity" functions;
I would assume that conductors identified with G/Y insulation must be reserved for earthing functions only.
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Re: Using the earth in control wiring as a control core?

Post by JamieP »

Thanks Alec, very in depth read

And I think you can also probably conclude that regardless of trying to get around it, it's quite clear that the green/yellow is only intended to be used as an earth in many situations, this situation feels like one when you know it probably shouldn't be but you are trying to find excuses, best to just do things right and avoid using it
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