electricalforum.nz

I know I've probably asked this before.. but I would be interested in some more opinions.

3.11.2 classification of wiring system.

After the clause.
NOTE: Underground wiring systems do not include those that are—
(i) embedded in a concrete floor, slab or pad; or
(ii) laid on the surface of the ground either within the building or in outdoor
locations; or
(iii) enclosed in a ventilated cable tunnel; or
(iv) enclosed in a trough with removable covers where air circulation is not
restricted.

In the case of (i), it isn't specified if that is inside a building or outside a building. I can't find any other clause that has specifics about inside or outside, referring to cables installed in concrete.

3.9.7.2 for example. Nor table 3.1
3.9.4 seems to deal more with interior locations.

The question is, if a wiring system is allowed in a floor slab within a building, where are the the clauses that say that a wiring system isn't allowed to be installed withing a concrete slab exterior to a building?

Such as lighting cables in a concrete drive or patio, or bonding conductors to fence posts in a concrete pool surround? I've seen plenty of instances where a conduit is run in the pool surround concrete, then core drilled through the conduit to run the bonding conductor to each fence post.

Certainly a good question, I just feel like there's no difference from inside/outside in concrete, if it's in concrete it's not buried and not an underground wiring system and as long as you comply with 3.9.7.2 (b)(I) and have it in an enclosure then I believe it's fine. Usually I apply 3.9.4.2 if within 50mm of the concrete surface even though looking at it now I'm not sure if it would apply to this sort of situation (interested to hear thoughts on this) and to be honest having a wiring enclosure and concrete probably means it is pretty sufficiently protected, I feel the requirements of 3.9.4.2 are there in regards to screw penetration of walls and such from people hanging things etc so it probably doesn't apply to a concert ground surface outside. Think I've just changed my own mind in regards to this haha

3.9.4.2 does apply in floors as well, so it should apply in concrete regardless of indoors or outdoors, although not specifically written for outdoor with the use of the word "floor" only. Which sort of goes along with my question, that wiring systems in outdoor locations and within a concrete slab, aren't really covered.

Interesting also to note that the "more than 150mm from an internal corner" location has been removed in 3000:2018. Can't say I've ever tucked a cable into a corner to use that rule anyway

The point of the Note after 3.11.2 is that the situations listed are deemed not to be "underground"; therefore the rules for u/g cabling [3.11] do not apply. And since item (i) doesn't specify indoor / outdoor (or any other limitation); ALL cabling embedded in a concrete "floor, slab or pad" is not "underground".
However many other requirements will apply.

eg 3.9.4 is not limited to indoor situations; so if the cable is less than 50 mm from floor surface (top surface of slab), 3.9.4.2 will deem it reasonably expected to be subject to mechanical damage. Certainly being fixed in the concrete it's unlikely to be able to "move freely" to further from the surface.
Similarly 3.9.7.2 may apply, depending on what type of cable is used. Eg TPS is unarmoured sheathe, so (b)(i) requires an appropriate wiring enclosure with special attention to reducing risk of mechanical damage.

The fact that there are no specific rules for a particular situation doesn't mean that situation isn't covered; just that it doesn't have any requirements that are specific to that particular situation.

Yes I agree that the normal enclosure and protection should apply.
And yes the note is just advising some examples of wiring systems that aren't underground.

So as there's no other requirement that directly states that a wiring system external to a building must be underground, or cannot be embedded in concrete on the surface, then running them in a drive or path must be fine?

I read it that yes, we can adopt such practice.
In the usual basis that anything that's not prohibited must be permitted.

I’m thinking they perhaps wrote that note ‘embedded in a concrete floor, slab or pad’ with pre-cast panels in mind.

So you can install a conduit or duct in a panel, prior to it being poured. Like when they make the panels off site for large projects etc.

If the Note had been intended to refer to eg wall slabs (tilt-slab construction"; it would certainly not have been placed in the "underground" clause.
There's no way anyone could consider a wall slab as being "underground" .

It's aimed squarely at floors, eg getting supply to equipment that's in the middle of an open floor area. The choices then are in-floor wiring (which the Note makes clear is not considered to be "underground"); or overhead dangly cables that may well get in the way of operations.