Dennis Galvin discusses the most important changes to Chapter 2 of the Standard.

The new edition of the AS/NZ3000 Wiring Rules will come into effect in November 2018, and Chapter 2 details how electrical circuits should be arranged, controlled and protected to ensure safety.

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 for the requirements of emerging products and technologies.

The 2018 edition contains several important improvements, including the requirements for residual current devices (RCDs), arc fault detection devices (AFDDs), electric vehicle charging, the arrangement of neutrals for residual current circuit breakers with over-current protection (RCBOs), and switchboard access.

Undoubtedly, the most important of these improvements are the new rules for RCDs. However, to fully understand them it is necessary to examine how the rules have changed over time.

I was involved in the original introduction of RCD requirements into the 1992 edition. As background research I analysed every record of an electric shock fatality in Australia from 1945 to 1990 that I could find to determine how many could have been prevented if RCDs had been installed.

RCDs would have made no difference in only two cases. In all the other instances, RCDs would have probably prevented the fatality. This made a hugely compelling case for RCDs to be mandated in the Wiring Rules.

Incremental approach

Two main problems with RCDs were identified at the time.

If an RCD trips on a lighting circuit, you lose all your lights, and for circuits feeding appliances such as refrigerators and stoves, leakage current tends to cause nuisance tripping.

Mindful of these concerns, the Wiring Rules initially recommended that RCDs should be fitted only on socket outlets. Interestingly, research indicated that this move alone would have prevented 87% of electric shock fatalities recorded between 1945 and 1990.

The requirement for RCDs on socket circuits was included in the 1992 edition of the Wiring Rules and implemented in Australia, although New Zealand mandated RCDs for sockets only in wet areas for fear that the costs would outweigh the benefits.

This view was subsequently revised when New Zealand introduced new insulation legislation, and five people died by inadvertently stapling through live circuits while fixing aluminium foil to the underside of floor joists. With RCDs in place, some – or perhaps all – of those 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 deaths. However, although the overall number of fatalities has dropped, electricians began to make up a disproportionally high percentage of those still occurring.

Analysis indicated that most of these ongoing deaths occurred 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 tackle the changing nature of avoidable deaths.

This provided the impetus in the 2007 edition to protect all final sub-circuits in residential installations with RCDs, including lighting.

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 downstream circuits and wiring.

To overcome the potential for losing all lighting if an RCD tripped, the Wiring Rules included a requirement for lighting to be split across at least two RCDs.

Until the latest revision, exceptions existed to prevent nuisance tripping for stationary appliances such as stoves. However, for Australia the 2018 edition stipulates that all final sub-circuits up to 32A for 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 electric shock is outweighed by the risk of a nuisance trip.

Commercial exceptions include equipment with high leakage current – such as 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.

Although this update will further reduce the number of fatalities, 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 probably 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. The Electrical Regulators Association blocked this move.

This will mean that older stationary appliances will need to be replaced.

There is another interesting implication in the new rules. When an existing unprotected circuit is extended then an RCD needs to be installed for the new section, but the existing circuit does not need to be protected.

This will probably increase the demand for socket-outlet RCDs, which have become virtually obsolete since the Wiring Rules required RCDs to be located in switchboards.

AFDD on the increase

Other changes to the 2018 edition include a recommendation for AFDDs to be installed in high-risk areas to prevent arcing faults and resulting fires.

AFDDs have had 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.

Although Australia has elected to recommend AFDDs for ‘high risk’ areas, New Zealand has taken a further step to mandate their use in schools that have accommodation, and in historic buildings.

In time, we expect AFDD requirements to expand, as has been the case for RCDs. There will always be an aspect of the Wiring Rules playing ‘catch up’ as the nature of electrical injuries shifts with the implementation of protective measures put in place.

Yet the changes to the 2018 edition will improve safety and help the industry to take positive steps towards a point at which deaths from electric fires and shock no longer occur.

Legrand technical director Dennis Galvin is an Australian Industries Group representative of the EL-001 committee responsible for changes to the Standards covering installation requirements.