I'm running a 100 amp feeder in mc cable with alumunum conductors.I called the store to ask how much 100 amp 3 wire alum. mc cable he had in stock.He said he had a full reel of #2 alum. 3 conductor mc cable.I explained that because this was a commercial job I could not use #2 because it only has an ampacity in these circumstances of 90 amps.He said commercial or not, everyone uses this for 100 amp feeders. I think if you used #2 alum. mc, you would have to put it on a 90 amp breaker if it was a lighting panel feeder,irregardless of a smaller load.I figure I'm right. Do you guys agree with me? Keep in mind I'm going to use a 100 amp sq-d nema3 enclosure and breaker as the service equipment that protects this feeder.