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.
Same building, just supply ground and neutral in appropriate sizes and separate, and be sure that ground and neutral are not bonded in the sub-panel.
6AWG copper (as a cable, which typically limits you to the 60C rating...) is maybe pushing it a bit depending how loaded that 60A panel is.