I've been thinking a lot lately about the environment and how, despite even the best effort, it always finds a way into machinery.
Most recently, this involved water getting into a junction box on a tugboat, even though the crew worked hard to prevent it. The J-box and the cable fittings entering it were wrapped in Densyl tape. The lid had a thick red silicone gasket. There was RTV silicone smeared around, as well. The crew really wanted that box to stay dry. And yet, when I opened it, the terminals inside were corroded, and I could feel moisture.
A couple of months ago, I opened a machine electrical enclosure to discover it filled with water up to the lower lip of the door flange. The box was Type 13, and all entries (conduits, wireways, cord grips, etc.) maintained that rating. This wasn't even a washdown environment.
At my previous employer (which did have many machines in washdown environments), the engineers and the workers in the service department expected to open an enclosure to discover standing water. The water may not have originated in that particular enclosure. Liquid-tight conduit can keep water out, or act as a pipeline keeping water in, and transfer it from one enclosure to another.
All of the components in the overall electrical assembly can be selected for proper ingress protection and still not be enough to keep the enclosure protected. In one memorable incident, the third-shift cleaning crew performed their job exactly as instructed, hosing the machine down completely with high-pressure water and caustics. They washed the machine completely, including the open electrical enclosure. That little incident cost the customer more than $20,000 in replacement components. That's an expensive but valuable lesson, if the lesson were learned. The same thing happened again a couple of months after the machine was repaired.
The fight against water ingress constantly escalates. It used to be that sensors were terrific if they had an IP65 rating (4psi water jet). As food plants increased their sanitation methods, this was no longer enough. IP66 became the standard (14psi water jet), then IP67 (3ft complete submersion). And then even that wasn't enough, and IP69K (1,200psi) is now the level necessary to protect sensors from water ingress from high-pressure hot water hoses.