Under the National Fire Protection Association (NFPA) 70E, a standard originally developed at the request of the Occupational Safety and Health Administration (OSHA), a permit for energized electrical work is mandated and can only be issued in two situations:
De-energizing, which would result in interruptions on essential life support, emergency alarms, or ventilation systems
De-energizing, which would introduce additional or increased hazards or be infeasible due to equipment design or operational limitations