Salt Air Corrosion: Why IP43 Marine Electronics Fail
An IP43 controller pulled off a dock at 18 months usually has salt on the board, green residue around the connector pins, and a warranty claim attached to it. The controller is not badly made. It was specified for a sheltered install and mounted in a marina.
What Salt Air Actually Is
Salt air is an aerosol of sub-micron particles, permanently suspended in any harbour, marina, or coastal environment. You cannot see it or feel it. It travels wherever air travels, which includes the inside of any vented electronics enclosure.
That last point is what makes it a different problem from spray. Spray arrives from a direction and a splash rating can exclude it. Aerosol arrives with the air.
How It Kills a PCB
Salt is hygroscopic: it pulls moisture out of the air. Once salt deposits settle on a board, they hold a thin moisture film on the surface even with no visible condensation. That film bridges copper traces, solder, and the trace metals between them, and the result is a galvanic cell sitting on the assembly.
The cell runs slowly and continuously. Nothing about it is visible until a joint goes high-resistance or a trace opens.
Two sources are worth reading if you are specifying for a coastal site. Verdingovas et al. (2014), in IEEE Transactions on Device and Materials Reliability, document the mechanism: NaCl contamination combined with humidity drives electrochemical failure of PCB assemblies at concentrations any coastal environment produces. Kim et al. (2023) measured corrosion lifetimes for printed circuit boards in marine atmospheres, and put exposed copper and solder in a 12 to 24 month window in a marine-class atmosphere.
That 12 to 24 month window matches what we see come off the dock.
What the IP Rating Tests
The second digit of an IP rating grades liquid protection from 0 to 9K. Each digit has a defined test method:
| Rating | Test | What it protects against |
|---|---|---|
| IPx3 | Water at 60° from vertical | Overhead spray |
| IPx4 | Water from any direction | Splash |
| IPx5 | Pressurised jet | Hose-down |
| IPx6 | Powerful jet | Heavy seas |
| IPx7 | Immersion to 1m, 30 min | Submersion |
Read down the right-hand column. Every one of those tests fires liquid water at a surface. None of them involves salt aerosol, because aerosol ingress is a separate failure mode that the IP scale was never built to grade.
So an IP43 enclosure in a marina is behaving correctly. It excludes water sprayed at up to 60 degrees from vertical, which is what IPx3 promises. Salt aerosol enters through the normal venting and settles on the board, and the rating never claimed otherwise.
Why This Gets Logged as a Product Failure
Installers report these failures as defects, and from the dock that is a reasonable read: the unit worked, then it stopped, and nothing obvious happened in between.
The mismatch is in the specification. The controller carries a rating designed for a protected indoor space. ISO 9223 classifies any harbour or marina atmosphere as C5-M, the highest marine corrosivity class. Putting a C5-M environment against an enclosure rated for sheltered mounting produces a predictable outcome on a predictable schedule.
For the installer the consequence is the same either way, which is a callback and a replacement unit. Knowing which failure it is changes what you do next.
What a Coastal Install Needs
IP67 is the rating that closes the aerosol path: dust-tight, and sealed against 30 minutes of immersion at one metre. No vents, no fan housing, no openings. Aerosol cannot enter because there is no path.
That single requirement drives the rest of the architecture. A fan needs a vent, and a vent is an ingress path, so a genuinely sealed controller has to be fanless and move its heat by conduction through an aluminium enclosure wall. Connectors have to hold the same rating as the housing, which is why sealed M12 connectors show up on every external connection.
We are building the MicroCore Marine Solar Charger to that architecture: IP67 end-to-end, fanless, M12 sealed connectors throughout. The enclosure and thermal design are specified and modelled; the hardware is in design and has not been through salt fog yet.
ASTM B117 salt fog testing is planned as part of validation, where 500 hours corresponds to roughly 5 to 7 years of marine exposure. New Zealand market entry does not require it. We are planning it because it is the evidence that answers the question an installer actually has, which is whether this one survives where the last one did not.
Next
The obvious follow-up question is which rating to specify when IP67 is more than you need. That is the next post in this series: IP43 vs IP65 vs IP67: What the Ratings Actually Test.
If you are specifying power electronics for a coastal or marina install and want a second opinion on the enclosure and rating before it is built, that is engineering consultancy work we do. We are based in Auckland and work remotely with teams in Australia and further afield.
MicroCore Systems, Auckland, New Zealand. jonathan@microcoresystems.co.nz