According to zxcvbob :

As I understand it, it's either 3 wire plus new ground electrode, or 4 wire with
no new ground electrode. In both cases with the ground/neutral lug _removed_
in the subpanel. Not a mixture of both. Ground loops.

If you run 3 wires (assuming 2 hot wires and a grounded neutral) you
most definitely do leave the bonding lug (screw) in the panel -- the
panel is a "service entrance".

We're talking subpanels (downstreams from main panels) here exclusively, not
separate service entrances.

If you leave the bonding lug in the panel, the subpanel's grounding goes through
the subpanel feed's neutral. Distinctly bad. Lose that neutral and all hell
breaks loose.

Subpanels always have their bonding lugs out. Either they get their grounding
from the fourth wire in the feed, or they get their grounding from grounding
electrode[s]. In neither case is it connected to the neutral.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.