Line to house blew out, wondering why?

My main feeder line from pole to house burned up and had to be replaced. It shorted out and I lost a phase, the insulation was burned with half inch gaps about every foot or so on the wire. I have 200 amp service, and three 240 volt appliances (spa, air conditioner and pool pump). The line was probably very old, as my house was built in 1959 (this could be why it happened). Edison replaced it with 4 gauge aluminum wire. My electrician said this isn't strong enough gauge, but it is what the building code calls for. I am wondering if running all three 240 applicances at once could cause this sort of thing, or if anyone ventures a guess what happened, trying to avoid same in future.