I looked at a condo today and all the branch circuit neutrals were burnt and corroded on the neutral bar in the condos panel. The feeder wires were 2/0 aluminum with a undersized neutral. I do not know the size of the neutral because the writing was worn off. My guess is that the feeder neutral was #4 aluminum but i could be wrong. The neutrals and grounds were isolated like it suppose to be for a feeder sub panel. The main service was 1000 amps and the breaker feeding the condo panel was a 150 amp breaker. i could not find anything wrong with the condos panel that would cause the neutrals to burn. All connections were tight. De ox was used on the aluminum feeders. My concern is why the neutrals are burnt. Is this simply from corrosion? I do not see any signs of water inside the panel like stains. There was quite a bit of dust and cob webs. What concerns me is every neutral was burnt on the neutral bar. I suggested changing the panel but am worried that something bigger could be going on here. Also are the feeder wire sizes even correct for 150 amps? if i am reading the NEC correctly it should be at least 3/0 for 150 amps when using aluminum. Any info would be greatly appreciated.