Corrosion might start small — a patch of rust on a hinge or some bubbling paint near a fastener — but left unchecked, it’ll eat through steel, break down seals, and let water get into places it definitely shouldn’t. And in our line of work, that’s a recipe for disaster.

We’ve seen boards installed in coastal areas that looked fine at first but were completely rusted through after just two years. One that comes to mind was a painted mild steel board up in Cairns — the salt air got to it quickly, and we ended up replacing it with stainless steel. That second board is still going strong, and it taught us an important lesson: corrosion resistance can’t be an afterthought.

What AS/NZS 61439 Actually Says About Corrosion

AS/NZS 61439 doesn’t just treat corrosion resistance as a nice bonus — it’s a mandatory part of design verification. That means if we’re building, assembling, or specifying a switchboard, we need to prove that the enclosure can withstand the environment it’s going into.

The standard gives us three ways to verify this: by actual testing, by referencing tested designs, or by following strict construction guidelines. This approach helps us avoid guesswork. It gives us a clear benchmark to check whether a material or finish will last the distance.

Severity A and B: What Those Mean

The standard outlines two levels of corrosion testing: Severity A and Severity B.

Severity A is aimed at indoor environments — clean, controlled settings like commercial buildings, shopping centres, or industrial control rooms. The test simulates moderate humidity and salt exposure over eight days. We did one job in a brewery where this kind of test made sense. The air was warm and humid, but not extreme. We made sure the board’s powder coating was top-notch and sealed properly — years later, it’s still holding up well.

Severity B is for harsher conditions — outdoors, coastal zones, and heavy industrial sites. It runs for 24 days and simulates salt spray, condensation, and temperature changes. We remember replacing a rooftop solar switchboard in Port Lincoln after the original one — a zinc-coated steel job — started rusting in under a year. The replacement was a 316 stainless steel enclosure, Severity B tested, and since then there have been no issues.

Choosing the Right Materials

The standard doesn’t dictate what material we must use — it just says we have to prove it will perform. That’s good, because it gives us options, but it also puts the onus on us to choose wisely.

For outdoor and coastal jobs, we almost always go with 316 stainless steel. It’s more expensive, sure, but it gives us peace of mind. For dry inland areas, aluminium can be a good lightweight option. Indoors, mild steel with a decent powder coat usually does the trick — but only if the finish is applied correctly.

We’ve learnt the hard way that corrosion always finds the weakest point. If sharp edges aren’t rounded before powder coating, or if someone drills into the board and leaves the hole unsealed, that’s where the rust will start. One small mistake can undermine an otherwise solid product.

Design Mistakes That Let Corrosion In

Even with the right materials, poor design can lead to corrosion problems. Flat tops where water can pool? That’s asking for trouble. Dissimilar metals that cause galvanic corrosion? We’ve seen that happen too many times. On one job in Townsville, the enclosure was 304 stainless, but the hinges were zinc-plated. It didn’t take long for the hinges to start rusting and jamming the door.

Gaskets are another common weak point. If they’re not UV-stable or properly compressed, moisture gets in. And once moisture finds its way inside, corrosion often follows. We always make sure gaskets are suitable for the environment and installed properly from the get-go.

Verifying That Our Enclosure’s Up to Scratch

AS/NZS 61439 tells us to verify corrosion resistance during the design phase, and we reckon it’s worth asking suppliers for evidence of that verification — especially if the job is in a harsh environment.

Just because an enclosure is rated IP66 doesn’t mean it’s corrosion-resistant. IP ratings deal with dust and water ingress, not how well something holds up in salt air over ten years. The best switchboard manufacturers will be able to provide test reports showing compliance with Severity A or B.

If we’re working with a local fabricator or a smaller brand, it’s worth digging a little deeper. Ask: has this material been tested? Are the coatings or finishes the same as those used in the verified design? If the answers are vague, we may need to rethink our choice before corrosion becomes our problem down the line.

Thinking About the Aussie Climate

Australia throws just about every climate at us — humid tropics, salty southern winds, dry deserts, and everything in between. That’s why the same board doesn’t work everywhere.

In Darwin, we had to choose an enclosure that could cope with extreme humidity. In Geelong, a chemical plant needed more than just stainless — we ended up applying a special epoxy coating to deal with acidic vapours. In the outback, UV exposure becomes a major factor, and ventilation has to be considered to prevent heat buildup and moisture condensation.

We always take the location into account, not just the spec sheet.

Don’t Forget the Maintenance

Even the toughest enclosures need a bit of attention. In coastal areas, we recommend rinsing boards with fresh water now and then to remove salt. It’s simple, but it makes a big difference. Regular inspections help catch early signs of corrosion — especially around fasteners and hinges.

We set up a quarterly maintenance schedule for a solar project near Geraldton, and those enclosures are still in top shape years later, despite the wind, salt, and sun.