What is a safe distance for building under power lines?

Local code will dictate the poximity. Use common sense and don't get excited by the cooks selling crystals or amulets to "shield" you from the "harmful" field. Once we all caught on to snake oil the carpet baggers of the 21st century jumped on the new age mystical bandwagon. Nothing better than a docrtine devoid of science that can't be refuted with science to peddle the wares to the unwary!