Bizarre breaker tripping on new circuit

[dlinscott]

Hope I qualify as "electrically related" since I have been involved in electrical/electronics since childhood and did all the wiring in my new home a few years ago. Added a sub panel with QO120DFC combination breaker in basement next to service panel to run some basement outlets. Got rough in inspection a couple days ago and decided to put in some outlets today. After adding a few decided to test and plugged in a drop light which immediately tripped breaker. Went to first outlet on string and isolated it - same result. Disconnected ground - same result. Popped in a regular breaker - no problem. Sub panel is not bonded - removed ground from service panel and checked to see if sub panel neutral and ground were isolated - checked OK. Disconnected Romex output from sub panel and jumpered connection from drop light (two different ones) to neutral bar and breaker output - breaker trips. Had to be a bad breaker so ran to Big Box Store to get another one. Same thing happens. I'm perplexed. Any thoughts on what is going on?
(Sub panel is fed with normal 50 amp breaker, 6 gauge hots, neutral and ground.)
Thanks!

 

[ActionDave]

I am closing this thread, in accordance with the Forum Rules.
This Forum is for professional electricians, inspectors, engineers, and other members of the electrical industry. We are not permitted to provide “how-to” assistance to a person who is not employed in this industry.