Bruce.
You are correct that if you follow a few rules you may run a 3 wire feeder in from the disconnect to the panel.
Here is the code article that allows this.
250.32(B)(2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of
(1) That required by 220.22
(2) That required by 250.122
Section 2 of this is very important.
(2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved,
One thing is still wrong according to your post
my GROUNDS in the subpanel, which ARE isolated from the neutrals in the panel.
This is wrong and dangerous, as you are feeding this panel without a grounding conductor you
must bond the neutral bar to the enclosure just like it was a main panel.
You are correct that you need a grounding electrode.
When you are allowed to run a 3 wire feeder to a panel you must treat this panel as a service panel, the bonding the electrodes etc.
The way you have it set up a fault from hot to ground will
not trip a breaker it will only feed current into one of your ground rods.
Feel free to ask more questions the members here will be glad to help.
Please read the code article I posted carefully and fully.
