"Exempt" means exempt from regular Confederate military service. That's possible for Powers based on occupation (which we don't know for 1860) or physical condition. He could have had a broken bone that didn't heal correctly. Otherwise he within the age bracket to serve.

"Detailed" means a soldier was enrolled in regular Confederate service, but assigned to duty away from primary regiment. Many soldiers unable to serve in the field were working on details in Columbus GA factories. In this case Powers should have been on roll with another command.

"Disabled" could mean a man had been wounded and was at home recovering as a convalescent. Again, in this case Powers should have been on roll with another command.