Introduction 

The introduction of the AS/NZS 61439 standards has had a significant impact on the approach to designing and building switchboards in the Australian market. With these new standards, this has clarified any ambiguities present in the previous standards. Such clarification allows switchboard builders and end-users to clearly understand and therefore, comply with these requirements.

The main changes and additions included:

• A new design verification process that replaced the TTA (type tested assemblies) and PTTA (partially type tested assemblies) concept
• The addition of tests to prove constructional compliance
• Additional options around conducting temperature rise tests

A major change in the standards was to recognise that more than one entity could be involved between early concept and final delivery of a switchboard. This led to a clear defining of the ‘original manufacturer’ and the ‘assembly manufacturer’.

The sharing of responsibilities can be explained as below. Original manufacturer (clause 3.10.1) e.g. Elsteel Ltd:

• Responsible for the original design, its verification and parts
• Full design verification completed by testing

Assembly manufacturer (clause 3.10.2) e.g. switchboard builder:

• Modifies the original design
• Prepares new design verification
• Completes assembly to the modified design
• Conducts routine verification
• Takes full responsibility for the completed assembly

Limits & restrictions

Specifiers, consultants, and end users need to be aware of the limits and restrictions of the new standards.

Device substitution - temperature rise (clause 10.10.3.5)

While the standard allows devices to be substituted (e.g substitute device A with device B, subject to certain conditions), it is critical to be aware of the fact that there are limitations with one of these conditions. Where this condition requires availability of data (power loss & terminal temperature rise) for both devices to product standard, and requires that values for device B are the same or better than device A, this condition is difficult to achieve because breaker manufacturers do not publish and share this information easily.

Derivation of busbar ratings for similar variants (clause 10.10.3.3)

In simple terms, extrapolation of busbar ratings is not allowed. Interpolation is allowed subject to the representative busbar arrangement being selected and tested according to clause 10.10.2.2.2, i.e same arrangement of bars and same centre line spacing of bars. It is important to note that to conduct interpolation a minimum of two similar busbar arrangements is required. If the arrangement changes (i.e. top to bottom location, or top to dropper configuration) then interpolation is not allowed.

Temperature rise verification (clause 10.10.2.3.5)

Another key point to consider is that temperature rise testing done to the old standard (complete assembly/RDF method) or tests done to the new standard (clause 10.10.2.3.5 complete assembly/RDF option) limits the ability to conduct verification by comparison. The new standard allows temperature rise verification by assessment/calculation for boards rated up to 1600A. However, this is subject to rules and penalties (refer clause 10.10.4) which can increase the switchboard size and costs when compared to a tested assembly. Temperature rise verification by assessment for boards up to 1600A doesn’t mean that the rest of the verification points can also be done purely by assessment. Those requirements need to addressed separately - for example, short circuit withstand strength cannot be verified by assessment.

Based on the above, unless design verification testing covering various ratings, busbar arrangements and with more than one brand of devices is done, then achieving compliance to the new standards can prove to be challenging for many switchboard builders. With the extensive testing done on the Techno modular switchboard system, IPD has the database and documentation to support switchboard builders to migrate easily to the new standard.

Techno - support & compliance

Elsteel has invested heavily in conducting design verification tests since early 2007. Several series of tests have been done with all major breaker brands, with busbar ratings from 400A to 6300A. The combination of multiple brands, switchboard ratings and busbar configurations has resulted in a large database of tested arrangements to assist in verification by comparison, as it is practically impossible to test each and every variant assembly. This is further supported by access to tested information via test reports, design and assembly information and design software.

The responsibility of the assembly manufacturer/board builder is to prepare switchboard layouts based on project specifications & single line diagrams. The board builder refers his design and requirements to IPD to conduct design verification and addresses their areas of responsibility to complete the process. Next, they assemble the boards to the modified design and conduct routine verification. The board builder is also responsible to provide full assembly information and documentation as defined in the standards (refer clauses 5.2 to 5.6, clause 6). IPD has been supporting Techno in Australia and New Zealand for the past 25 years. To ensure that this new process flows efficiently, the IPD technical team have set up a structure to provide switchboard builders with the necessary tools to comply with the requirements
of the new standards. These tools include: training & accreditation, design & estimation assistance, assembly drawings, and techno assembly assistance.

Specific design verification assistance covers:

• Selection of incoming circuits, main, distribution & PE conductors
• Selection of devices, cell sizes & related conductors
• A design verification compliance statement with supporting documentation
• Providing access to view type test and design verified test reports

To understand more on the standards, our compliant indoor and outdoor switchboard solutions and to discuss our support/compliance documentation in more detail, please feel free to contact IPD.