Wiring Rules 2018: Part 2, Section 2
Let’s look at the overall power distribution architecture of an installation, including required functions and features, all under the Section 2 heading ‘General arrangement, control and protection’.
This section deals mainly with power distribution. It focuses on:
- control and isolation for maintenance, testing, fault detection and repair;
- automatic disconnection of supply for over current, fault and earth leakage currents;
- protection against over-voltage and under-voltage conditions;
- suitable arrangements for switchgear and control gear groupings, locations and access;
- controlling and protecting reliability of other parts of the installation in case of faults; and
- verifying that switchgear and control gear installation is to manufacturer instructions.
Electricity distribution in all installations has to be arranged, installed and controlled.
It involves controlling voltages and currents that can be a shock hazard and generate considerable operating temperatures.
These hazards increase as currents and voltages get higher, especially in switchboards or environments that are already at increased temperatures. Poorly selected or installed switches, circuit breakers and other current-carrying devices can result in harmful and destructive failure, and a much-reduced service life.
This makes emphasis on careful selection and reference to manufacturers’ instructions crucial to an installation’s performance, as most equipment has quite different ratings in different environments. Switchgear and control gear can even be destroyed if improperly used.
For instance, the rating for a piece of equipment in ‘free air’ can be much higher than when it is in a small compartment – or if surrounded by items also generating heat.
This is reflected in some of the changes in this section and in the new Appendix K ‘switchboard requirement summary’.
Changes listed in the ‘preface’ include:
- adding switchgear operating characteristics;
- origin of sub-mains identification;
- operation of main switch details;
- position and alternative positions of overload device clarification;
- expansion of discrimination requirements;
- enhancement of switchboard arcing fault protection;
- additional and revised RCD requirements;
- clearances around switchboards clarified (and increased);
- guidance on the use of low-current arc fault detection devices;
- enhancement of requirements for 800A and over switchboards; and,
- clarification on rising mains and other tee-offs.
Substantial changes from the 2007 edition in Part 2 Section 2 include:
- New item (f) under ‘selection and installation’ placing more emphasis on compliance with additional requirements in manufacturer instructions for different ratings in different installed environments. Refer also above. (p75)
- A note is added under arrangement of electrical installation (d) drawing attention to the need to increase reliability of supply as further detailed in new Appendix M. (p76, p559)
- New heading ‘origin of sub-mains and final sub-circuits’ requiring every sub-main and sub-circuit to commence at the main switchboard or a distribution board and for all the ‘live’ conductors to be connected at one switchboard’ is inserted and ‘common neutral’ renumbered. (p76)
- New heading ‘electric vehicle charging circuits’ is added referencing Appendix P and special NZ requirements. (p77)
- The heading now ‘common control systems’ (was ‘common requirements’), ‘general’ is elevated to a sub-section heading now covering new sub-section heading ‘all systems’. The previous headings are renumbered to follow. A new item (d) adds that the precautions now also include short-circuiting and earthing as supplementary measures. The word ‘poles’ under ‘direct current systems’ is changed to ‘conductors’. (p80-81)
- Under ‘devices for isolation – general’ the word ‘supply’ between ‘active’ and ‘conductors’ is deleted to now include all active conductors, not just the active supply conductors. Also, the word ‘shall’ has been moved to each of items (a) to (f) as the opening word. So, there is no material change apart from emphasising that each (a) to (f) must be complied with. (p82)
- New sub-heading ‘introduction’ is slotted in under ‘main switches’ above the otherwise unchanged wording below. The later sub-headings are renumbered to suit. Also, the ‘exception’ under sub-heading ‘general’ dealing with main switches for alternative or supplementary supplies is reworded and the (a) to (g) numbering is now 1 to 7. (p83-84)
- Word ‘operation’ is added to ‘location’ for the heading to now read ‘operation and location’. A new note (b) dealing with main switch operating handles and controls requiring manual operation and excluding electronic touch screens for main switch operation is included with the remaining clauses renumbered to suit. A new item (e) has been added detailing labelling requirements for any supplementary or alternative supply to identify the energy source. Under ‘remote control’ new item (iii) preventing overriding or bypassing by PLC or similar and new item (d) for additional requirements where touch screens or PLCs, etc, are used in conjunction with a main switch are added. (p84-86)
- Cross-reference list under ‘appliances and accessories’ now includes (i) ‘gas appliances and accessories’ and (k) ‘lifts’ with the remainder re-indexed to suit. (p88)
- Under ‘emergency switching including emergency stopping’ the paragraph mandating an isolating device where there is a risk of shock is reworded but does not appear to change the intent. (p88)
- Text under ‘emergency switching devices’ has slight rewording of (v) for manual reset prior to starting but no apparent change of intent. (p89)
- Text under ‘fault protection’ in (b) has added compliance cross-reference to cl 5.7. (p92)
- Text under ‘protection against over current’ has a new sub-heading ‘general requirements’ with renumbering of the other sub-headings to suit. Also, a note at the end of that clause dealing with reduction in current-carrying capacity numbered as Note 1 and reworded, with Note 2 referencing Appendix I (ratings of imperial cables) added. (p94, p540)
- Text under ‘consumer mains’ (b) and (c) now does not refer to note (6) and text is added after (c) that this arrangement is regarded as unprotected consumer mains with a clarification note for unprotected consumer mains and cross-referencing added. A new figure 2.1 follows. (p94, p95)
- Note under ‘sub-mains and final sub-circuits – general arrangements’ is changed to now refer to 2.2 (A) and 2.2 (B). (p96)
- The exception under ‘devices for protection against both overload and short-circuit currents’ is now referenced to 126.96.36.199. Note 4 regarding screw-type fuses now refers to an IEC document. (p96)
- A substantial clause ‘characteristics of short-circuit protective devices’ has been moved from later in this part of the Standard but not changed. The other clauses are renumbered to suit, the figures likewise. The figures are also reworked with changes. Users should acquaint themselves with any changes. (p99-100 and Figures 2.3 to 2.10)
- The first paragraph under ‘protection against switchboard internal arcing fault currents’ – ‘general’ is reworded to include the 800A and over reference previously included in the note. There has been no change of intent. (p108)
- The first paragraph under ‘reduction of the probability of the initiation of a switchboard internal arcing fault’ replaces the previous term ‘heavy current switchboards’ with the term ‘switchboards rated at 800A or greater per phase’ to clarify the 2007 edition intent. (p109)
- Figure 2.11 is included, showing which are parts of a functional unit and which are not. (p110)
- Cross-reference to 188.8.131.52 (a) is added under ‘protection afforded by separate devices’. (p111)
- Under ‘co-ordination of protective devices’, a paragraph is added with detail on back-up (cascading) of devices with a note to use manufacturer instructions and a reference to new figure 2.12. The references in Note 2 are re-homed, and a Note 3 added to clarify selectivity need not apply where protective devices are in series on the same circuits, such as with UPS connected supplies. (p112-113)
- Under ‘safety service circuit discrimination (selectivity)’, ‘selectivity’ is added to the heading and the text is revised to mandate the previously more loosely worded requirements so that the original intent is reinforced. The references to figures are re-homed. (p113)
- Under ‘general supply circuit discrimination (selectivity)’, ‘selectivity’ is added to the heading and the text revised to mandate the previously more loosely worded requirements. So, the original intent has now been reinforced. The use of discrimination studies has been included in the main text; it was previously included in the notes. The reference to figures is re-homed. (p113-115)
- Under ‘types of RCD’ an additional IEC Standard IEC 62423 is added. Advice for users to consult the RCD manufacturer for type selection and Australia-only and New Zealand-only requirements are added. (p120-123)
- The heading ‘additional protection by residual current devices’ is renamed from ‘where additional protection is required’ and it has been changed substantially, including a virtual blanket requirement for RCDs on all final sub-circuits in domestic and residential situations. In addition, all RCDs must be installed at the switchboard. In non-residential installations RCDs must be provided on all socket-outlet circuits, lighting circuits, direct-connected hand-held electrical equipment and direct-connected equipment that represent an increased risk of electric shock. In non-domestic non-residential situations, for direct-connected type circuits up to 32A, the installing of 30mA RCDs should also be considered. There are exceptions and other changes, therefore users are advised to carefully study the new edition so that these requirements are fully understood. (p119-125)
- In ‘home care installations – Australia only’ RCD requirements must comply with AS/NZS 3003 and some of these may need to be Type 1 RCDs rated at 10mA. (p125-126)
- Under ‘alterations to installations and replacement of switchboards – Australia only’ RCDs must be installed where any sub-circuit is altered or socket-outlets are added. Also, where all the circuit protection on a switchboard is replaced, unless certain exemptions apply. For repairs, where a socket-outlet, luminaire or single item is replaced ‘like with like’ RCDs are not mandated. There are also some NZ-only requirements to note for NZ users. (p126-127, p130)
- Heading ‘protection against fire hazard due to arcing fault’ is new, inserted in place of ‘switchboards’ which is renumbered to suit. Low-current arcing faults, as in faulty electric blankets and other appliances, and damaged wiring and electric cords have been identified as potential sources of house and building fires. Low-current arcing fault detection devices (AFDDs) have now become available for use in situations where the owner or occupier identifies such risk. The information here and in new Appendix O is for guidance in Australia but AFDDs are required in some situations in NZ. Further details are included. (p133-134)
- The Section 2 clause ‘switchboards’ has been renumbered as also noted above. The previous exception is numbered 1 and a second exception added dealing with tee-offs and short branches where a smaller conductor may be used for up to 3m, or alternatively for those circuits to be otherwise protected. ‘Accessibility and emergency exit facilities’ (a), (b), (c) must now all be complied with and the distances/spacing around switchboards are changed as detailed in the text and the diagrams. This increases the access space to a minimum of 1m but retains access of 600mm from the open arc of switchboard doors to other open doors (i), (ii). A minimum of two emergency exits are now mandated for switchboards 800A and over or 3m long unless there is a 3m or greater clear space in front. (p134-139)
- A new header sentence is added under ‘location of main switchboard’ requiring (a), (b) to be complied with. All references have been re-homed to reflect the numbering change of the switchboard clause, and Note 3 under (k) has been split into two to clarify the NZ requirement. (p140-143)
- The reference under ‘construction’ is re-homed. A requirement is added covering the ‘suitability’ of the environment in which the switchboard is installed. A note (1) is added referencing Appendix K ‘switchboard requirement summary’ and the other notes renumbered. A new heading ‘orientation and location of circuit breakers’ has been inserted and the second paragraph under the moved sub-heading ‘orientation of circuit breakers’ has the word ‘exception’ removed, making this a normal requirement. A new clause ‘location of fuses and circuit breakers’ setting out grouping requirements and prohibited locations is added. (p143-144, p545)
- Heading ‘bars or links’ is reduced to ‘bars’ and the word ‘link’ removed from the entire text (and will most likely fall out of use in situations applying to connection bars). The references have been re-homed. There’s a minor edit in the wording of ‘exceptions’ – ‘is not necessary’ to ‘need not apply’. (p145-147)