Uh, "WHAM! Sparks everywhere coming from sub panel." and "I’ll check with a morning swim." shouldn't be uttered with the same breath! Have your electrician buddy come by first.
I wanna say there is no circumstance in which properly wired circuits and sub panel would throw sparks from the sub panel. Is that what happened? I've seen sparks at a receptacle, and a light switch or light fixture, but not at the panel. Maybe I've just never been looking at one in the dark, but I sure wouldn't get into that pool until I knew exactly what happened. Do you yet?
Please be careful, and smart, about what you're doing...
(Smiling!). Electrical is serious, but yes, it does sound nuts to swim! Who does that?
Let me clarify, I just want to move front to back on possible reasons. Want to see if there’s water in pool light. I strongly doubt this is source, but wanna check. Before I jump in tomorrow, as now-breaker is now off, pool lights are disconnected and covered by wire nuts at light jbox. NO chance of danger.
Also, this problem child is only one breaker, the other 2 breakers that power pump and heater are working fine, no issues.
Before I took a break for the night, I got the breaker back on and spa pump fired back up—no sparks. Breaker is working fine again. Turned it off though. I presume if I were to push RESET button on GFI I’d have fireworks and trip.
Problem is either bad ground or short from GFI jbox, or something downstream at pool/spa lights. My strong suspicion is it’s bad ground. Gonna check my work, remove paper washer, add the ground wire pigtail and then I’ll wait to have my electrician check it.
Never seen a larger CB trip in darkness, but it was ‘jolting’ by the blue flash-and loud snap of breaker. Could have been totally normal protection response (let’s hope).
I never had any electrical issues ever since replacing the GFI, so I really think it’s something ground related-at that jbox.