X10 is a protocol for communication among electronic devices used for home automation where the signals involve brief radio frequency (RF) bursts over a home's A/C power lines.
Household wiring often has two different power circuits; each of the two 220V offers a single phase circuit to neutral. This means if the X10 controller is on one of those 110V circuits, the signals are not passed to the other of those circuits.
The solution to this is to bridge the two 110V circuits so the RF signals may pass between them. This question is about what the specs for the capacitor should be if we wanted it to be very reliable over time.
I bought and installed a capacitor like this (for a dollar) and it worked for probably five or more years:
But then it failed, and looked like this when I found it:
Capacitors, when operating properly, do not conduct [significant] current across their leads, but this season (putting up Christmas lights), the signals were not passing to all outlets, and when I looked in the breaker box, the capacitor had dropped away and fallen to the bottom. The leads were gone (apparently melted). So the dielectric apparently broke down over time and the capacitor failed.
This got me to thinking, would there be a higher quality / higher spec capacitor that would be less likely to fail? If it meant I could count on it when I needed it, for decades to come, it would be worth spending more on it. But I don't know what to buy. I suppose I could install more than one, then if one failed, I'd have another. But I'm not going to be pulling the cover off of the breaker box to see if one or the other blew. Obviously not a critical problem, but just curious if there's a solution where a little more investment would mean no problems in the future.
Follow-up Appended Edit:
I ordered another one from the same place as I got the one the that had earlier failed: