While visiting another furum I read a disscusion on sub panels.They must have 4 wires back to the main panel.They also stated in the main panel the neutral and grounds must be separated and not bonded together at main panel.If you have only 3 wire service at the main panel the grounds and neutrals would have to tie or the ground fault path wouldn`t trip the breaker. Did I totally miss something.was it a type o.
