My house had a subpanel in the bedroom closet that was being fed from a main panel outside the house. I am in the process of upgrading to a single 200Amp main panel and replacing the subpanel with a 10in x 10in x 4in junction box in the attic fed by seperate circuits from the main. At this time there are 6 15 amp circtuis feed in this manner. Can anyone tell me whether the code allows a single ground wire from the main connected to a ground bar inside the junction box or whether seperate ground lines for each circuit bonded to the junction box are required?