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AS/NZS 61439 is a series of standards for low voltage switchgear and control gear assemblies for the Australian and New Zealand market. Our previous article gave a broad overview of the new testing and verification processes that are now required as part of the standard.

This article goes into more detail of some of the key changes that will have an impact on low-voltage switchgear and control gear assemblies, as well as manufacturers who need to be aware of the changes in order to comply with the new standard.

We cover 3 of the key changes now in place. Temperature rise, device substitution and arc fault mitigation.

Temperature Rise

Considered to be one of the most important tests to be undertaken to gain certification under AS/NZS 61439 is the temperature rise tests. In the previous AS/NZS 3439.1 the

temperature rise limits for all components and busbar systems within the enclosure was 105°C.

The new standard sets a maximum that now takes into consideration the ambient temperature and calibrates this so that the main busbar can operate at 105°C above the ambient temperature.

Normally switchgear is calibrated at 35-40 deg C operating temperature and higher operating temperatures would mean derating the circuit breakers as per the manufacturer data. With the ability to now operate the main busbar at a higher temperature, this can allow greater current carrying capacity.

With this, there are however, other considerations take into account. When running the main busbar at higher temperatures it will take its toll on mechanical strength and lifespan of the copper.

Copper bar will “soften” at temperatures above 150 ⁰C, can operate successfully at 105⁰C for periods of 25 years, and can withstand conditions as high as 250⁰C (under short circuit) for a few seconds without any adverse effects.

Here is a rough a comparison of lifespan values for busbar operating at a continuous temperature of:

• 105⁰C = 20 to 25 years

• 110⁰C = 17 to 20 years

• 130⁰C = 11 to 18 years

Therefore, you may want to consider the maximum operating conditions and limit the temperature rise within the overall design of the assembly.

Verifying temperature rise can be done by:

Testing the assembly and/or

Derivation from/comparison with tested design and/or

Calculation with a single assembly not exceeding 630A, or a multi-compartment assemblies less than 1,600A

All three methods may be used for verification within the same main switchboard.

Device Substitution

Another important feature with the 61439 series of standards is that the complete assembly is verified to comply. The IEC standard does not allow substitution between brands as the AS/NZS version does.

If you start to make additions or alterations to the design, then the person doing these changes takes on the responsibility for this altered design and needs to ensure the updated assembly is verified to comply with the 61439 standard – the original manufacturer is no longer responsible.

When a switchboard developer or manufacturer produces a new switchboard system, they must test it with several different devices.

Switchboard builders may want to substitute alternative devices from those originally verified by the system designer. The new IEC Standard can be difficult to navigate when considering the question of device substitution.

Appendix ZA in the AS/NZS document varies the requirements and provides clarity on when device substitution and verification by comparison with reference design and/or calculation is permissible – even between manufacturers – up to 3,150A when specific parameters are met. Above 3,150A, verification by testing is required when devices are substituted.

Arc Fault Mitigation

A final key change is arc fault mitigation. Arc fault mitigation is set in place to reduce the probability of an internal arcing fault. This is to protect personnel from injury in the event of a fault and to limit the extent of damage to equipment in the event of a fault.

Arc fault containment to the guidelines of Appendix ZC, subject to agreement between customer and manufacturer, and tested in accordance with Appendix ZD, came in under AS/NZS 3439 and has been retained in the new standard.

In most cases an internal arc fault would cause major damage to a switchboard thus rendering it unusable without repair or replacement.

The new standard allows European arc fault containment testing in accordance with IEC TR61641 to be used as it is comparable and acceptable to Australian Standards. . IEC/TR 61641 applies techniques commonly used for high voltage applications. The IEC arc fault containment test requirements are more descriptive and robust thus giving a higher level of safety.

In both instances, the end user and switchboard manufacturer agree to the testing criteria. Both are equally satisfactory in providing arc fault testing results in accordance with customer requirements. Arc fault containment tests as defined in Appendix ZC and ZD.

If you need assistance navigating the new standards we can help. AutoControl Systems has over 30 years of industry experience. We are committed to remaining at the forefront of our industry by using leading-edge technology to deliver precise, strategic thinking across every project to turn your concept from vision to reality, providing bespoke solutions that drive productivity and profitability.

Please contact the team for more information (08) 9258 4555 or emailsales@autocontrols.com.au

Auto Control Systems is dedicated to providing clients with innovative automation solutions customised to suit your specific application

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