Short-circuit strength verification may be performed by one of three means. The first and most straightforward way is by physical testing in a controlled setting. This is done by applying fault current to the assembly to assure it is still intact. The second is by comparison with an existing reference design that has been previously tested. If the new design has the same busbar structure, materials, and enclosure fabrication as the tested one, then it may inherit the same rating. Assessment by calculation is the third method. This is only permitted under severe conditions and normally for lower fault levels or simpler systems.

No matter which method is employed, it has to take into account the behaviour of all live conductors—phase, neutral, and earth—and mechanical components such as busbar supports and terminals. The whole system has to be intact and safe after the fault has been removed.

The Role of Temperature Rise Testing

Rise in temperature testing is another important requirement. Although switchboards produce heat even under normal condition, particularly at higher currents, if this heat is not handled well, it may cause insulation to degrade, speed up material ageing, or even thermal runaway and fire.

The standard imposes definite limits on the amount of internal temperature that can be elevated above ambient conditions. Copper busbars, for instance, are restricted to a maximum of 105°C above ambient, generally translating to a maximum total temperature of approximately 140°C in Australian conditions. Other terminals, circuit breakers, and plastic supports also have definite limits of temperature based on their material and insulation class.

Checking Thermal Performance

AS/NZS 61439 offers the same three alternatives for checking temperature rise performance. Testing is once more the most certain approach and has to be undertaken with the full assembly, including all covers and parts in position. This guarantees the heat dissipation within the enclosure to be realistic.

Alternatively, the new board can be compared to an earlier tested version with identical layout and heat characteristics. Calculation is also allowed, but in established limits. In particular, calculation techniques like in IEC TR 60890 can be employed in assemblies of up to 1600 amps, as long as the compartmentalisation and ventilation conditions are similar.

Why Temperature Rise is Important in the Real World

The effects of poor thermal design can be severe. If a switchboard is repeatedly operating beyond safe temperatures, components can degrade fast, insulation can become brittle, and the assembly’s overall life can be greatly shortened.

For example, busbars working at their thermal limit of 105°C can last for 20 to 25 years, but any rise in temperature will reduce it by half. It should be remembered that switchboards usually work in hot Australian conditions, at times in unventilated conditions or outdoor enclosures, and thus temperature management becomes even more essential.

A Practical Example: 1000-Amp Board Design

To put this into context, imagine you’re designing a 1000-amp main switchboard for a commercial facility. The switchboard will need to be tested or verified to handle both the expected operating current and a potential fault current—say 50kA for one second. If you’re using a module system that has already been type-tested by the company, you might be able to fall back on the reference design approach, provided your implementation is within the bounds of that system.

But if you do any changes—e.g., alter the spacing of the busbars, change the enclosure, or include components from a different manufacturer—you will likely have to re-test or re-verify to prove compliance. The same goes for temperature rise calculations; if your board consumes 1000 amps full-time, and you’ve modified the ventilation or compartmenting of the enclosure, calculation might not be enough—you might have to perform a complete thermal test.

Modular Systems Make it Easier to Comply

The wonderful thing about current switchboard systems is that most manufacturers now offer completely verified modular systems that are tested to AS/NZS 61439. These systems enable panel builders to combine tested building blocks to create switchboards within the compliance envelope. It makes it easier and provides peace of mind.

That being said, the onus is still on the panel builder to make sure that any modifications or tailor-making are accurately accounted for and validated. Compliance is not inherent merely because a system is branded—it’s a matter of how components are put together and deployed. Another key point is documentation. AS/NZS 61439 requires each switchboard supplied under the standard to be accompanied by a declaration of compliance. This document should include the rated current, fault withstand rating, and method of verification applied for short-circuit and temperature rise performance.

If calculations were applied, the assumptions and details have to be provided. If comparison was applied, the reference design has to be named. If testing was performed, the outcomes have to be present. It’s not satisfactory to simply state a switchboard meets requirements—the documentation has to demonstrate how.

What Installers and Contractors Should Watch For

It’s also important that electricians and contractors inquire the proper questions when buying or mounting a switchboard. Don’t rely on a bright new board being compliant because the devices are rated properly. Request the records of verification. Verify the declaration of compliance. Make sure that the rating for short-circuit is for the complete assembly and not only the circuit breakers. Make sure that the test for temperature rise was conducted with the same layout and enclosure being installed.