Electrical supply protection standards

A number of new electrical supply protection standards have recently been updated, simplifying the process of providing supply protection.

I spoke with Phillip Tompson, Novaris technical director, Dennis Galvin, HPM chief technical officer, and Steven Davey, PowerCom Solutions sales manager about recent supply protection standards updates and their implications for contractors. Tompson represents the Institute of Engineers Australia on Standards Australia committee EL-024 (protection against lightning) and was recently commissioned to write an appendix on risk assessment for the draft AS3000 Wiring Rules and to rewrite the AS4070 standard. Galvin is a member of EL-004 (electrical accessories) committee and several subcommittees. Davey trains consulting engineers and apprentices on lightning protection.

AS1768

Thomson: "Electricians often fail to realise that electrical systems have components above 50 Hz that are influenced by inductance, which are addressed by lightning protection systems. The new AS1768 includes a 'Risk Assessment calculator' to identify if buildings need structural or surge lightning protection, or both. For example, broadcast sites with antennas and towers are self-protecting because of their substantial earthing and paths-to-ground down the towers. The risk calculator would identify that they're structurally protected from lightning strikes, but would also identify power coming to the sites as a possible surge threat. Used as intended, it guides electricians and engineers through a process to identify all the potential risks and then provide adequate protection against them.

"Building owners rely on their electricians to make their premises electrically safe, but often electricians assume surge protection isn't needed, or that it's someone else's responsibility. There might be adequate surge protection in the grid, but it's often neglected for buildings. This standard, which is recommended in the new Wiring Rules, should emphasise its importance.

"We also changed the design approach for lightning protection on buildings, so that it's more effective in identifying strike-prone areas and containing the cost by not unnecessarily overprotecting buildings. Research proves that lightning strikes the corners or points of buildings, so AS1768 suggests a two-stage process to address it. Firstly, ensure all points and corners of a building are protected with air terminals (rods) connected to conductors routed to ground. Secondly, use the 'rolling sphere' method to assess the risks to the rest of the building."

Davey: "The new AS1768 provides a single method of assessing protection products, because the industry has used differing methods in describing its protection. For example, I_max defines a product's mode's protection, but some manufacturers add all mode protection together, which confuses contractors. To illustrate, three-mode surge diverters rated at 40 kA normally have three MOVs deployed for A-N, A-E and N-E. The overall I_max is still 40 kA, however some suppliers claim they're rated to 120 kA."

AS4070

Thomson: "I rewrote AS4070 to expand on the previous version, explaining why inductance has such an impact on electrical systems, and then how to install electrical systems to be more effective in combating surges. I've covered how to install diverters for both main and subdistribution boards, with explanations of all the modes to be encountered and the differences between them.

"AS4070 provides practical cautions on overcurrent: "All surge-protective devices must be considered as loads. Like any other load, they must be protected by overcurrent fuses or circuit-breakers. The choice of overcurrent protection is not straightforward because the SPD (surge protection device) normally draws little or no current from the AC supply. The fuse or circuit-breaker must safely isolate the SPD should it fail, yet it must allow the rated surge current to pass without failure."

Davey: "AS4070 explains to electricians that surge diverter leads should be installed as straight and as short as possible to reduce inductance. Due to the rapid rise time of surge pulses, lead-length may allow large let-through voltages across a circuit, so an incorrectly designed system could be tragic.

"Surges can be induced into any conductive cable, whether it's for power, TV, phone, data, broadband, intercom, CCTV or control. They're all potential surge paths, so they all must be addressed to adequately protect premises.

"All surge products require an earth to be present. We've seen sites where earth-stakes were installed years ago and the drought has left them with no conductivity back to the neutral connection on the power lines. Some farmers using SWER lines have had to disconnect from mains totally and generate their own power."

AS3000

Thomson: "While it's not mandated, my appendix offers simple guidelines for electricians to carry out a risk assessment, suggesting how surge protection may be useful for an installation and how to go about it. It's a step in the right direction."

Davey: "The revised AS3000 helps electricians better understand surges, but it's not enough. If the appendix was made mandatory, all electrical installations would be better protected from surges."

Galvin: "The Wiring Rules committee decided not to mandate the use of surge and lighting-protection devices. This is representative of a much larger regulatory issue that the electrical industry needs to address. The industry wants uniform, countrywide application of standards but, like many other industries, state regulators apply different interpretations of standards in approving products. Some regulators don't allow the sale of various products in their state, even though they're approved and being sold in other states.

"ERAC, the electrical regulators coordination committee, is organising a review of the way regulations are applied in different states.

"Industry bodies, such as AEEMA, promote uniform rules and want electrical safety to be administered by the federal government but aren't having much success. They want approval schemes that mandate products be certified as standards-compliant before they can be sold, whereas regulators in some states want deregulation, relying on self-declaration to ensure safety, proposing compliance through post-market intervention. Industry bodies however, would rather prevent unsafe products getting on the market instead of prosecuting after people have been injured by unsafe products."

Supply protection standards

AS/NZS 1768:2007	Lightning protection
AS 4070-1992	Recommended practices for protection of low-voltage electrical installations and equipment in MEN systems from transient over-voltages
AS/NZS 3015:2004	Electrical installations - Extra-low voltage DC power supplies and service earthing within public telecommunications networks
AS 4262.2-1999	Telecommunication overvoltages - Protection of equipment
ENA EG1-2006	Substation Earthing Guide