Thanks for the kind words and your question is a good one often asked.
Heres the deal as brief as I can make it (Engineer and Attorney mind you lol). If you supply a sub panel fed from your main panel, to that sub you carry sufficent Hot UnGrounDED Conductors (2, L1 & L2 for 120/240),,,,,,,,A Neutral GrounDED Conductor,,,,,,,,,An Equipment GroundING Conductor.
At the sub the Neutral Buss and Equipment Ground Buss ARE TO REMAIN SEPARATE AND ISOLATED. Yes that means any tie bar (N to G) is removed HOWEVER the panels metallic case frame, same as any other metallic enclosures, requires a bond to the equipmet ground which may be accomplished by a screw that goes from the ground buss into the frame BUT THATS NOT THE SAME A N TO G TIE BAR MIND YOU