I want to replace the old Stab Lok sub panel in my detached cottage with a new Square D. I notice that the Square D has no ground buss. Is it OK to add a buss to the panel?
The existing panel only holds two breakers with the grounds from the service wires simply twisted together. There is no ground rod. I will run a proper ground rod and wire to the new panel.
If it's a detached structure, they'll all be together anyway, but yes if you need more room you can add a grounding bar. The ground and nuetral will be bonded anyway if you're adding a ground rod, as you should and have said you are.
Whether or not the detached structure needs a ground bar in the square d panel is dependent on the feeder to the detached cottage sub-panel.
If it has a 3 wire feeder and no metal water pipes or raceways etc connecting the house to the cottage then the sub-panel ground and neutral bars are bonded or are simply the same bar and grounds and neutrals are terminated together on that bar. You would install the green bonding screw in your new square d panel.
If the feeder is four wires then the ground and neutral are seperated at the sub-panel. This will require you to buy a seperate ground bar for the square d panel and install it to the can of the panel utilizing the predrilled holes. You would not install the green bonding screw square d uses in its bonding design. The grounds will go to the ground bar and neutrals to the neutral bar/bars. A 4 wire feeder will be required if any metal connects the main structure to the cottage.