electricalforum.nz

3.4.1

"In New Zealand only, wiring systems in domestic installations shall be
installed on the assumption that thermal insulation in ceilings, walls and
under floors, if not currently installed, will be installed in the future."

My question is should be be assuming partiality or fully?

This requirement means that some form of de-rating must be applied.
Whether 'partially surrounded' or 'completely surrounded' is appropriate depends on circumstances.

For any ceiling or floor where there is currently no BTI; the cables being installed will be lying on or secured to structural elements.
When BTI is added; the cable will become partially surrounded.
(Moving the cables so that they are no longer touching the structural elements would be PEW).

Walls are a bit different; as cables are generally not installed so as to be touching the lining / cladding, but rather tend to be approximately in the middle (due to the requirement for mechanical protection if within 50 mm of wall surfaces).
This increases the likelihood that cables in walls may become fully surrounded - especially if the BTI used is spray-in foam or Insulfluff.
Even with batt-type BTI; Building Code requirements have increased to the point where proper installation of the BTI requires it to be placed on both sides of the cable.

Accordingly partially surrounded would be a reasonable assumption for floors & ceilings; but fully surrounded would be reasonable for walls.
For most circuits; some part of the run will be in a wall; and this becomes the governing factor for CCC of the cable (refer clause 3.4.6 of "3008.1.2")


Note that in 2018 edition; this is no longer NZ-only. Also has an Exception such that when extending or altering an existing circuit; the requirement applies only to the new / relocated wiring, not to existing parts of the circuit that are left in situ.

Thanks.

So if the cable is in the wall for more than 400mm meeting the definition of fully surrounded it should be rated as such.

Photos attached for future learning

Yes

Dan L wrote: ↑

Wed Aug 02, 2023 8:09 pm

Thanks.

So if the cable is in the wall for more than 400mm meeting the definition of fully surrounded it should be rated as such.

Photos attached for future learning

Unless it's clipped so it can't be fully surrounded.