Wiring Rules 2018: Part 2, Section 3
As with the selection of equipment, there are many cabling aspects to consider that may adversely affect an installation.
Section 3, ‘Selection and installation of wiring method’ is the glue that binds the supply and distribution equipment in Section 2 to the ‘consumer’ devices in Section 4, so the installation architecture delivers the intended outcome.
The size of cables, where they are installed, how they are protected and how they are supported or held in place can catastrophically affect the cables themselves, the installation, the safety of people nearby and the ultimate life of the installation.
In order to deal with some of these issues, the Standard now includes additional requirements to protect cables from damage in places such as walls, where they are concealed and may be damaged during activities as innocent as the hanging of a luminaire, picture or shelf.
The focus on energy efficiency and the retrofitting of thermal insulation have prompted the extension to Australia of a previously NZ-only requirement. This covers wiring above ceilings, in walls and under floors to cater for – and be based on – the installation of thermal insulation.
For safety, identification of the origin of any sub-mains in an installation or to outbuildings must now be noted on the distribution switchboard supplied by the sub-main.
Now that wiring enclosures above roofs for PV installations are more prevalent, some guidance is provided on not interfering with the free flow of rain water and on the prevention of debris being trapped.
Changes listed in the ‘preface’ include:
- improved safety requirements for cables passing through bulk thermal isolation;
- clarification of requirements for wiring systems likely to be disturbed;
- clarification of cable segregation from different installations in common enclosures; and
- segregation of cables of different voltages.
Substantial changes from the 2007 edition in Part 2 Section 3 in page order include deletion of ‘presence of’ in sub-headings for ‘humidity’, ‘foreign bodies’, ‘substances’; a new subheading ‘mechanical damage’ replaces ‘impact’; and, further deletion of ‘presence of’ for ‘flora’, ‘fauna’. There is no material change. (p153-P155)
- The new heading ‘thermal insulation’ clarifies which AS/NZS3806 ratings to apply where cables pass through insulation, as these now vary depending on the length of transit thru the insulation. (P155)
- The previous NZ-only requirement dealing with domestic wiring having to be based on ratings for thermal insulation in ceilings, walls and under floors is now applicable to Australia.
- The now- applicable switchboard Standard AS/NZS61439 for busbars and busways is added in Note 4. Australian users should understand this requirement, as it may affect the selection of cable size and type. (p155-156)
- Text under ‘connection methods’, ‘common requirements’ (e) is expanded and reference made to the switchboard Standard for switchboard terminals. (p154)
- Text under ‘identification’ and ‘exception’ on there being no restriction on cable sheath colour has been moved up from the notes below, reducing the notes to 1 and 2 but with no other change.
- Cables with yellow, green or yellow/green sheath colour are not permitted for cables with active and neutral conductors in Australia. A reference to the switchboard Standard AS/NZS61439 is included.
- Note 4 under Table 3.4 is added that the only permitted colour for neutral conductors in NZ domestic installations is black. (p168)
- The heading ‘colour identification’ is added and ‘colour identification by sleeving or other means’ completely redrafted, including for the prohibition on using a green, yellow or green/yellow as an active or neutral conductor.
- There are additional requirements for the sleeving of earthing and bonding and existing live conductors. The exception immediately below ‘exceptions and special applications’ is changed to re-home references and add the reference to Table 3.4.
- A new note (d) for a multi-core cable with a green earth is included and the note (b) further down on conductors in flexible cords (except for yellow) has been expanded.
- See also the note immediately above for prohibited cable sheath colour for active and neutral conductors. (p168, pp169-170)
- In the ‘wiring systems likely to be disturbed’ paragraph, ‘location’ is shortened and the requirement for ‘support and protection’ added separately as a new sub-clause. It clarifies the support requirements and contains a statement that RCDs shall not be used in lieu of mechanical protection for wiring systems likely to be disturbed.
- The first paragraph under ‘wiring systems near building surfaces’ has been edited but not materially changed. The new Figure 3.3, detailing treatment of such wiring (e.g.: behind a recessed or wall-mounted switchboard) is also included. (p173-174)
- Additional information on the type of mechanical protection deemed to comply is included under protection methods (a) and (b), and there’s a note after (c) further clarifying where earthing of the protection means need not be provided. (p177)
- The grammar of the first and second paragraphs under ‘particular installation requirements’ is changed but the intent remains as before. (p177-178)
- The arrangement of text under ‘different electrical installations’ is changed with sub-headings ‘common enclosure/cable’ and ‘segregation’ added, replacing the previous (a) and (b) and stipulating in greater detail which cables can be in a common enclosure and which must be segregated. (p181)
- The heading ‘electromagnetic interference’ is changed to ‘minimisation of electromagnetic interference’. There has been no change to the text. (p188)
- Under ‘wiring enclosures’, ‘types’ (a) wording in the first paragraph is changed to include the new Standard AS/NZS61386. There is no other change. (p189)
- The wording under ‘installation of wiring enclosures’, ‘general’ is changed. The overriding paragraph remains the same but the specific requirements for enclosures installed on roofing materials are now detailed. This is at least in part due to these installations becoming more widespread, with the wiring to PV cells, etc. There is particular focus on the requirement to avoid obstructing water draining paths and promoting debris accumulation. (p190)
- A note is added under ‘installation requirements’, ‘general’ highlighting that there are further details and figures later in this section. It should be noted that some of these are new, e.g.: for cables installed on a sloping site or near and behind a retaining wall (Figure 3.17). There is no material change. (p196-202).