As an apprentice I would assume your electrical skills are minimal. So, the amount of time it will take for you to complete a 'piece' will be longer than typical which translates to you making less than someone with more experience. As you learn and increase your skill level the amount of 'pieces' you complete in an 8 hour day will increase thus increasing the amount of money you will make.
If you are a motivated individual than getting paid by the piece can work out for you. If you are the type who shows up for work because you have to and has little/no motivation, than being paid by the hour would benefit you more (and hurt the employer)
