Adding a 60amp sub panel (4breakers) on the 2nd floor for a dehumidification system and some misc. Running 100 feet of 6/3 wire. I am assuming that I can use the ground wire in the 6/3 from that sub panel ground bar to the main panel ground bar. This is not in a separate building so I don’t think NEC requires grounding rods. And if so does anyone know the limitation on the length of a ground wire if indeed a separate one is required for the panel itself. Washington country Maryland.