Surge protection standards

Electrical equipment is designed to strict applicable standards in Australia. However, business and consumer products such as power supplies, commercial and industrial equipment, computers and televisions are coming under pressure and the focus is now on design to minimise cost.

This approach relies on specified mains voltages being maintained 100% of the time to supply standards. The equipment you install, domestic or commercial, may not necessarily be able to handle significant variations in mains power quality.

However, utility suppliers can no longer guarantee absolutely error-free power - with so much aboveground copper, it’s next to impossible to achieve. Even 99.9% guaranteed power within specification still leaves 5256 minutes a year of potential power problems. Site infrastructure may also contribute to power anomalies from power-hungry facility features such as gensets, lighting systems, motor sets and air conditioners.

All it takes are a few microseconds of unregulated power to create the damage. And remember it is not just AC mains that can be a problem. Any conductor, coaxial cable, internet cable and phone line can also deliver harmful energy to your equipment if you get a surge.

Most equipment is now designed overseas in accordance with overseas regulated surge protection standards and therefore relies on some surge protection already existing in the system.

Currently in Australia there is no regulated protection standard. It is not compulsory to fit surge protection. This means that the electrical equipment used in Australia may be relying on the upstream protection that simply doesn’t exist to do most of the work in handling harmful surge events.

So why isn’t the equipment designed to handle surge events?

There are two primary reasons: first, the smaller the power supply, the less able it is to absorb harmful energy events; the second reason is that trying to deal with excess energy at the final point of entry into equipment is the wrong place to alleviate the problem.

It is almost impossible to divert the harmful energy safely once it is inside the equipment. The co-located printed circuit boards and low-voltage components are too close. Even minor increases in voltage will result in damage to circuits. The harmful energy must be dealt with before it reaches the equipment. The requirement to do this is now moving to end users who need to provide a secondary protection level in accordance with emerging standards.

Installing surge protection before installing electrical equipment also makes sound economic sense as it increases the longevity of the investment. The cost is really small compared to the investment. The users should view it just like insurance. You insure your expensive car, so why not insure your expensive electrical equipment?

There are a few guiding principles and standards that can be applied to any site. The overall guiding principle is to divert the energy then control the surge current flow. Then, do it again. Sounds simple? There are, however, quite a few standards that apply. Key to understanding the correct approach to the solution is to understand what standards can be applied and where. It is also important to understand that there is a strict hierarchy of standards.

Foundation standard

Fundamental to all surge protection standards is ANSI/IEEE C62.41. This foundation standard was developed many years ago in the US - based on research on surge energy events, a risk or protection zone strategy was developed. This zone strategy basically states that surge energy should be broken up into zones within a site. Surge protection devices (SPDs) are installed and matched to each zone. Only in this manner can the entire infrastructure be effectively protected.

Risk assessment standards

The Australian Standard AS/NZS 1768 relates to how to measure risk and determine placement and type of surge protection required on a site. AS/NZS1768 is not a mandatory standard. It mirrors much of ANSI/IEEE C62.41 and is, therefore, an appropriate standard. However, this standard is not a standard to certify an SPD against. It is basically a risk assessment standard. Once the risk level and zone are determined, the user needs to select appropriate surge protection devices and locations for specific installation.

SPD standards

In Australia there is no mandatory SPD certification standard. The country predominately uses either UL1449 or IEC61643. The latest revisions of these, at the time of writing, are UL1449ed3 and IEC61643-11. These US and European standards do vary from each other in some key performance measures and practices but either is suitable for use in Australia. These devices are usually rated against a specific risk category. In US products, the protection devices are classed as Type 1, 2, 3 or 4 devices for use in Cat A, Cat B, Cat C, Cat D risk zones. In European products, these protection devices are classed as Class I, Class II or Class III devices for use in each risk zone. It’s important to select an SPD that matches the risk zone it is being applied to.

Installation standards

Correct installation of an SPD is very important. Most manufacturers give precise installation instructions. Sometimes, the cost of installing an SPD can be more than the value of the device itself. There are, however, no shortcuts to a good result. By following guidelines in AS/NZS3000:2007, Appendix F and taking note of manufacturer recommendations, a good result can be achieved.

By using the zones protection principles, any site can be broken down into a number of risk areas. Once the risk is determined, a suitable SPD can be selected and applied to do the job. In a typical commercial or industrial site, the solution will most likely have three or two zones of risk.

Zone 1 - This zone is typically the point of entry into a site. It is usually the zone of highest risk and therefore it is the location to place an SPD with the highest performance characteristics. While in UL1449ed3 terms these are usually Type 1 or Type 2 devices, in IEC61643-11 terms these are Class I or Class II devices. These devices are primarily surge diverters - they divert the primary surge voltage and absorb some of the current.

Zone 2 - This zone is typically a distribution board or sub-board fed from the MDB or point of entry switch. It is usually the zone of medium risk and therefore an SPD with lower performance characteristics can be placed here. In UL1449ed3 terms these devices are Type 2 and in IEC61643-11 terms these are Class II devices. Here there is an opportunity to make a key change in the type of device to be applied - ie, either a surge diverter or combination diverter and surge filter. The key difference here is that with the surge diverter you only divert the energy, but with the surge filter you can divert the energy and control the surge current flow to the next zone. Surge filters use inline inductors to add this extra dimension. They cost a lot more but deliver a lot more as well.

Zone 3 - This zone is typically the final sub-circuit or end-user equipment. It is usually the zone of lowest risk, but not always. In this zone the physics of what is happening in current and voltage means that there are limitations as to what can be effectively achieved. Therefore, ensuring installation of a device with good overall performance characteristics in terms of voltage and current limiting is very important. In UL1449ed3 terms these devices are Type 3. In IEC61643-11 terms these devices are Class III. In this zone it is typical to fit a combination surge diverter/filter. They can be hardwired or portable plug-in types. These types of devices can also provide protection for conductors other than mains AC - ie, internet cable, phone, data line, coaxial etc. Remember, the zone protection principles need to be applied in at least two locations/zones to get an effective result.

Following the above principles can ensure effective protection against surge events. Other power quality events require different technologies. UPS systems, power conditioners, power factor correction and isolation transformers are all used to perform different corrective functions.

By Mike J Hale, Surge Protection Engineering and Product Manager, Eaton Corporation, Australia & New Zealand.