I am running a subpanel off of a mdp. the mdp is 1200 amps 480/277 volts. I'm running a 3- 500's which are good for 380 amps as the ungrounded conductors and (1) 1/0 for the grounding conductor. My grounded conductor(neutral) load is about 100 amps. Whats the minimum size grounded conductor I can run and where would I find it in the NEC?