As an intro, my electrical service is unusual (I think). Prior to upgrading to 200 amps, here is what I had: Meter on outside of attached garage. Power came through garage wall and into a 100 amp fused pull disconnect. The disconnect output ran across the garage ceiling and down into my basement. In the basement was a standard 100 amp service pannel (upgraded from fuses to breakers).

I purchased a welder, and wanted power where the disconnect was located it the garage. So, I purchased a 200 amp main breaker pannel with throughfeed lugs, and went through the propper channels for upgrading to 200 amp service (utility company, inspector, etc). The throughfeed pannel has six slots for breakers, and big lugs for the power to run to my original 100 amp pannel (still protected by 100 amp main breaker).

I put in new grounding rods and cable for the new 200 amp throughfeed pannel, however, the feed to my 100 amp pannel in the basement is only three conductors (2 encased and one braded around the outside). Obviously, I need to add something to the basement pannel to properly ground or separate neutral and ground back to the 200 amp pannel. My 100 amp pannel in the basement has all the grounds and neutral wires on common bars.

So here is my question, should I run a ground wire from my 200 amp pannel (which is properly grounded) to my 100 amp pannel, or should I run a new ground system (2 more rods, etc) for the 100 amp pannel. If I run another wire from my 200 amp pannel to the 100 amp pannel, do I need to isolate the neutral and ground circuits?

Thanks for the help!