ECN Forum Forums Code Related Discussion NEC & other Code issues Sub panel

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.

I believe that either it was misstated in the discussion or you misread it but in the service equipment the EGC's and the service equipment enclosure are bonded to the grounded service conductor (i.e. the neutral). This provides the fault clearing path.

Do you mean:

[1] neutral
[2] (red) leg
[3] (black) leg
[4] Grounding conductor

The service does not provide a grounding conductor. That's why the service has only three conductors. The GEC at the service is where the grounding conductor comes from and it can only be connected to the service neutral at one point and that is at the service.

After reading your post again. Did they leave out the main bonding jumper?