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Wiring Rules 2018, Chapter Two: ensuring a less shocking future

The 2018 Edition of the AS/NZ3000 Wiring Rules will come into effect in November 2018. As an Australian Industries Group representative of the EL-001 committee responsible for the changes to the standards for installation requirements, Legrand Technical Director, Dennis Galvin, is perfectly placed to discuss the most important changes to Chapter Two of the Rules.

Chapter Two of the Wiring Rules details how electrical circuits should be arranged, controlled and protected to ensure safety. Prior to the 2018 Edition, the last update to the Wiring Rules was published in 2007. The revisions for each new update not only represent a step forward in electrical safety, but also allow the needs of emerging products and technologies to be addressed.
The 2018 Edition contains a number of important improvements, including the requirements for Residual Current Devices (RCDs), Arc Fault Detection Devices, electric vehicle charging, the arrangement of neutrals for Residual Current Circuit Breakers with Overcurrent Protection (RCBOs), and switchboard access. Undoubtedly, the most important of these changes are the new rules for RCDs, but to fully understand the importance of the new regulations it is necessary to look how these have changed over time.

I myself was involved in the original introduction of RCD requirements into the 1992 Edition of the Wiring Rules, and as background research I analysed every record of electrocution fatality in Australia from 1945 to 1990 that I could locate to determine how many of these could have been prevented if RCDs had been installed. I identified only two cases where RCDs would have made no difference: in all the other instances, RCDs would have probably prevented the fatality. This made a hugely compelling case for the use of RCDs to be mandated into the Wiring Rules.

Incremental approach

Two key problems were identified at the time with RCDs. Firstly, if an RCD trips on a lighting circuit, you will lose all your lights; and secondly, for circuits feeding appliances like refrigerators and stoves, leakage current tends to cause nuisance tripping. Mindful of these concerns, the Wiring Rules initially recommended that RCDs should only be fitted on socket outlets. Interestingly, research indicated that this move alone would have prevented 87 per cent of those electrocution deaths recorded between 1945 and 1990.
The requirement for RCDs on socket circuits was included in the 1992 Edition of the Rules and implemented in Australia, although New Zealand only mandated RCDs for sockets in wet areas for fear the costs would outweigh the benefits. This view was subsequently revised when New Zealand introduced new insulation legislation, and five deaths resulted from people inadvertently stapling through live circuits while fixing aluminium foil to the underside of floor joists. With RCDs in place, some—or perhaps all—of these deaths could have been prevented.
Over time, the requirement for RCDs has increased in Australia and New Zealand, with a consequent dramatic reduction in the number of electrocution deaths. However, while the overall numbers of fatalities has dropped, electricians began to make up a disproportionally high number of those still occurring. Analysis indicated that most of these ongoing deaths occurred either from drilling into wiring, or making contact with exposed live parts where electrical insulation had broken off in roof spaces.

Exceptions abatement

Clearly, the regulations needed to address the change in nature of avoidable deaths, and this provided the driver in the 2007 Edition to protect all final sub-circuits in domestic and residential installations with RCDs, including lighting. In practice, this meant that instead of locating RCDs in the socket outlet itself, it was more practical to position the RCD in the switchboard, thereby protecting all the circuits—and the wiring—downstream of the switchboard. To overcome the potential to lose all lighting if a lighting circuit RCD tripped, the Rules included a requirement for lighting to be split across at least two RCDs.
Until the current revision, exceptions still existed to prevent nuisance tripping for stationary appliances like stoves, but for Australia the 2018 Edition now stipulates that all final sub-circuits up to 32A for domestic and residential installations have to be RCD protected. The only remaining permissible residential exceptions include relatively rare equipment—such as home dialysis machines—where the risk of electrocution is outweighed by the risk of a nuisance trip. Commercial exceptions include equipment with high leakage current—like variable speed drives or ovens—which would trip an RCD through normal operations, or those processes requiring high-reliability circuits. Under the 2018 Wiring Rules, New Zealand still permits exceptions for RCDs for stationary appliances.
While this update will undoubtedly further reduce the number of electrocution deaths, it will be at the expense of nuisance tripping. For instance, older equipment with heating elements that have not been specifically designed to repel moisture ingress will likely experience leakage current that will cause repeated RCD trips. A possible compromise that was discussed was for stationary appliances to be fitted with 100mA RCDs instead of 32mA, which would eliminate most of the nuisance tripping issues, but the Electrical Regulators’ Association blocked this move.
In practice, this will undoubtedly mean that older stationary appliances like stoves will need to be replaced. Another interesting implication to the new rules is that when an existing unprotected circuit is extended an RCD needs to be installed for the new section of the circuit, although the rest of the existing circuit does not need to be protected. This will likely increase demand for socket-outlet RCDs, which have become virtually obsolete since the Rules required RCDs to be located in switchboards.

AFDD on the increase

Other changes to the 2018 Edition include a recommendation for Arc Fault Detection Devices (AFDDs) to be installed in high-risk areas to prevent arcing faults and resulting fires. AFDDs have suffered a chequered history, as normal current flow in some types of equipment can be interpreted by an AFDD as an arcing fault and cause nuisance tripping. However, the greater sophistication of the latest signal processing technology allows for better protection with fewer nuisance-tripping issues. While Australia has elected to recommend AFDDs for ‘high risk’ areas, New Zealand has taken a further step to mandate their use in schools with accommodation, and in historic buildings.
In time, we expect AFDD requirements to expand, as has been the case for RCDs. While there will always be an aspect of the Wiring Rules playing ‘catch up’—as the nature of electrical injuries shift with the implementation of protective measures already put in place—the changes to the 2018 Edition will undoubtedly improve safety and will help the industry take positive steps towards a point where electrocution- and electrical-fire-related deaths no longer occur.

Tags: AFDD, circuit, compliance, Legrand, Legrand Australia, Legrand New Zealand, RCDs, regulation, safety, Wiring Rules