Suppose a 4-conductor cable is connected to a printed circuit board mounted inside of a waterproof enclosure. The cable may become damaged (the insulation may be breached) allowing water to seep into the cable jacket and even into the individual conductors, which now behave as water pipes that bring the moisture right down to the board. This will happen regardless of any external waterproofing measures.
Assuming the impure water does not short any of the conductors, there is now a risk of corrosion at the solder connections on the board, as well as additional moisture damage to the rest of the board. Furthermore there is a risk that over a long period of time, this water may actually fill up the enclosure, destroying the board and everything connected to it.
The cable is epoxied into the enclosure containing the board so no water can come in around the outside of the cable, but there is no protection against water coming in through the inside of the cable and the individual conductors.
This can't be a new problem, there must be a practical solution out there for this already but I have yet to find it. Sure, I could apply epoxy around the individual conductors as well where they come into the enclosure but 1) that would be a manufacturing nightmare, and 2) there could still be air bubbles or delamination of the epoxy that would allow water through.
Does someone have any experience with this and have any suggestions for how to prevent water ingress from the inside of the cable?
Best Answer
First: Epoxy-ing a cable through a hole is no guarantee for anything at all, as epoxy is rigid and doesn't form cross-bonds with almost any other plastic and plastics work with temperature just as any other material. (and also: moving the cable may just as well open cracks)
Second there's a reason IP67+ enclosures of professional grade only employ IP67+ connectors (fully sealed) and no direct pass-through of cables.
If you intend on using direct pass-through you're likely going to need to fill the enclosure with something flexible, like potting silicone.
You can attempt more aggressive glues like poly-acrylate on holes and cable-ends, but those are dirty stuff and even their cross-bonding depends on the types of plastic.
Truly the only "good" work you can do for high moisture resistance is actually getting all of the right materials as you'd find in industrial applications.