I have added a sub panel next to my main panel. It is fed from a 100A breaker using 3-3-3-5 CU Service wire. I removed the ground screw to isolate the Neutral and I installed the ground bus that came with it on the left side. It is attached with 2 screws directly to the panel. I connected the #5 ground wire to this ground bus.

The question:
The ground bus is SHORT with only 8-10 usable positions so I have added an additional ground bus on the right side of the panel. It is made specifically for the panel, Square D and attaches with 1 screw, centered over 2 nubs that lock it in place. Is the screw enough to ground this additional bar or do I need to interconnect it to the first ground bus with wire. If so, what size?

Thanks VERY much in advance for your assistance!

Follow up:

INSTRUCTIONS!! Those would VERY handy indeed. The problem is that they SUCK. Number 4 gives all the info about how to wire it, but I found it less than useful. Here is the entire text of the instructions:

1) Turn off all power to the enclosure

2) Mount grounding bar to the back of enclosure:

• if one mounting hole and two nubs are provided, mount with outer holes over nubs and mounting screw through center hole.

• if two mounting holes are provided, mount with two mounting screws.

  NOTE: If no mounting holes are provided, use #26 drill bit to drill two 0.147 in diameter mounting holes using grounding bar as a template.

3) Apply equipment grounding label to enclosure beside grounding bar.

4) Install wiring to grounding bar. See equipment grounding label for binding screw torque.

So are they assuming this is the ONLY grounding bar and therefore the #5 ground feed from the main panel will get attached to it? Or is the lack of instruction to jumper it to an existing main ground bar an indication that the screws are enough and that it grounds through the body of the enclosure to the original ground bar? I sure can't tell from what little info they provided.