Problem: My single pole 15A DF breaker has blown twice (I stopped after the second time) at the hot connection point in a newly installed outdoor sub panel.
My goal: I recently installed two new sub panels off of my main as the main was full. I wanted dedicated outlets in the garage for some big tools (sub 1 - indoor) and a panel for new pool equipment (sub 2 - outdoor).
My wiring: Sub 1 is up and running with no issues. Sub 2 has the problem. In the main I have 2AWG hot 1, hot 2, and neutral with 1AWG ground. I connected hot 1 and hot 2 to a 90A double pole breaker. Neutral and ground are connected to the neutral/ground bar.
I have all running up into the attic and about 75 ft across the house, out to a junction box and down conduit to sub 2. All conductors are jacketed individually, have some sort of reinforced ribbon wrapped around them all together, and then jacketed again as one. I’ve only removed enough outer jacket and ribbon at the main, junction, and sub 2 to move my wires to their places and fasten.
In sub 2, hot 1 and hot 2 are connected to their individual lugs. Neutral is connected to the neutral bar and ground is connected to the grounding bars via lug which is bonded to the chassis. The neutral and ground are isolated from each other. There is no bonding screw. All home runs (except ground) have antioxidizing gel at each connection point.
I am using a 15A DF pigtail breaker for use with my panel (Homeline). Sub 1 is the same except that it has plug-on-neutral breakers instead of pigtails. This sub 2 breaker is currently only connected to a 15A outdoor light switch with a 15A outdoor floodlight. Light grounding, bonding, and wiring are all good and run with 14/2. Breaker wiring has load hot to the brass terminal, load neutral to the silver terminal and the pigtail going to the panel neutral bar. I intend to run 3 more dedicated outlets for the pool equipment but haven’t yet with this issue present.
What happens: when I turn on the sub 2 power at the main 90A breaker, everything is fine. When I turn on the breaker, it blows at the connection point where it sits on the panel hot. There is a visible spark and audible pop. (This is with no load; I haven’t tried turning on the light and nothing else is wired to the breaker or the rest of the panel yet). Additionally, the 90A main breaker does not trip.
Inspection: There are no signs of shorting or arcing on any of the wiring. There is a clear burn/scorch mark on the panel hot connection terminal and on the breaker itself where it snaps into the panel hot. Nothing else on the breaker or panel.
Lastly: I haven’t tried any other breakers or any of the other 5 breaker positions in the panel yet. I didn’t want to risk blowing again and having a bigger problem. To note: the specific panel hot contact I was using has the incoming neutral lug connection right above it but is separated by internal plastic (panel design). The other positions have bits of plastic protrusions as well but this connection has the most and is the closest to the incoming neutral.
So sorry this was so long but I wanted to be as detailed as possible and I’m not sure what next steps to take or troubleshoot. Thanks for any help you can offer.