Wire Splitting at Epoxy Seam

I potted this cable McMaster-Carr using Loctite marine epoxy and the potting kit sold at blue robotics, got a very clean initial finish and the connectors even passed the vacuum seal test. I had to remove the penetrators for regular maintenance and when I went to put them back, the cable jacket had very cleanly split where the epoxy met the cable. Is this because of chemical properties in the epoxy, or is it maybe too hard and not allowing any movement without breakage?

It’s hard to say. If the seal has been working well before releasing after some time in use then it seems unlikely to be specifically a chemical issue. I’m aware that potting sometimes fails due to exposure to temperature extremes, but it’s unclear how you’ve been storing and transporting your equipment so no idea if that’s likely here. It can also fail if exposed to too much pulling/stress.

It’s worth noting that difficulty in achieving consistently robust and reliable results with potting, and in predicting when a failure is likely to occur are key reasons we’ve developed and predominantly moved to using compression-based WetLink Penetrators. Where possible we’re also working to develop epoxy-less alternatives for our other products.

From a post on why the (potted) BlueESC was discontinued:

@Makenna,I might be able to shed some light on this issue; a couple of years ago we were producing some transducers which were epoxy potted. The transducers were approx 5mm diameter with a 1mm coax output cable and we were producing these in quantity.

The biggest drawback was a 62% failure rate whereby the coax was snapping off at the epoxy interface. As part of the QAQC we did some (expensive) Destructive Tomographic Analysis which involves shaving layers off the component, and each layer is photographed under magnification.

What we found was the epoxy shrinks and leaves a small - but significant - meniscus against the cable. When the epoxy hardens this forms a circular knife edge around the cable, any movement results in a cut through the cable itself.

There are a number of ways you can mitigate but it really depends on the application and cable size/composition.