NFPA 410 section 18.104.22.168 requires "To reduce the hazards associated with static electricity, aircraft shall be electrically grounded when parked in aircraft hangars."
Boeing Aircraft are statically grounded thru the aircraft tires as required by specification. I would assume this is the same for Airbus model aircraft. If the hangar floor is uncovered cement or painted with a conductive paint or plugged into ground power (pin 4 of stinger is earth), the airframe is grounded to earth.
An aircraft sitting in a hangar is not developing a static charge anymore than my car sitting in my garage.
Aircraft are electrically bonded during fueling. I do not understand the term electrically grounded. Aircraft can be statically grounded thru designated static grounding points provided by the manufacturer...
I do not understand the purpose of this restriction.