Confused on what to do in this situation, or if there is a problem... here's the setup:
I have a main panel and a subpanel. Main has ground bonded to neutral and sub panel has bonding screw removed to separate them.
I then have a METAL double gang outlet box that contains some splices.... inside this box is a junction that ties 3 of the main panel 20 amp 12 AWG wires together on an outlet branch and no devices. The #12 is THHN fed via PVC not EMT to the box.
I need to add a 3-way switch into this box (part of a 4-way circuit) that is on a 15amp branch that is driven from the subpanel. The new 14/3 romex coming into the box is just runners for the switch - so 3 hots and a ground.
My first instinct is just to tie all the grounds together, but if I do that then the 15a lighting circuit now has a direct ground path to the main panel that doesn't go through the subpanel route.
My other option would be to ground the 14/3 ground to the box and tie the 3@ 12/2 grounds together but not to the box.
Any pointers on the best approach and why?