At least in the US, minimum separation is for when you're talking to air traffic control, and MSA is for flying on instruments. Minimum separation when you can see outside and aren't talking to ATC is "don't hit other planes." Minimum altitude is 500ft, or 1000ft over "congested areas," plus 500ft distance from any obstacle. Unless you're flying a helicopter (or powered parachute or hang glider) in which case the only requirement is "the operation is conducted without hazard to persons or property on the surface."

It would make sense for a quadcopter to follow helicopter rules. Obviously it does not follow the "without hazard" requirement if you crash into cables, though.