A: Yea, the wire range for THQP2150 is 8-3 Cu/8-3 Al. Thank you for your question.
A: Yes but #6 is not rated for 125A because
A: Thanks for the question. Yes this breaker accepts #6-1/0 CU and #4 - 1/0 AL.
A: You mean in the main breaker position? Probably not. A Siemens 200a breaker is a lot bigger physically. But the 125 should plug into the branch circuit bussbars ok.
A: I just noticed this is a GE breaker. It’s probably not UL listed for use in a Siemens panel. Nit recommended.
A: yes . but it is not recommended
A: No don?t even try
A: It might.
A: Greta Question! A GE breaker is only UL approved for use in a GE panel.
A: The torque value will be written on the breaker itself.
A: Absolutely it will. Thanks for the question.
A: Maybe. Some 200a panels have a 100a maximum for branch-circuit breakers. Generally you need to look at the manufacturers specs on the piece of paper glued to the panel cover door and see what model of breakers can be installed in that panel. If the 125a is listed there you’re good to go.