Sealing requirements specified in Sections 501-5(a)(4) and

(b)(2) shall apply to horizontal as well as to vertical boundaries of the defined Class I locations. Raceways embedded in a concrete floor or buried beneath a floor shall be considered to be within the Class I location above the floor where any connections or extensions lead into or through such location. 513-8. Aircraft Electrical Systems. Aircraft electrical systems shall be deenergized when the aircraft is stored in a hangar, and, whenever possible, while the aircraft is undergoing maintenance. 513-9. Aircraft Battery - Charging and Equipment. Aircraft batteries shall not be charged where installed in an aircraft located inside or partially inside a hangar. Battery chargers and their control equipment shall not be located or operated within any of the Class I locations defined in Section 513-2 and shall preferably be located in a separate building or in an area such as defined in Section 513-2(d). Mobile chargers shall carry at least one permanently affixed warning sign to read: "WARNING - KEEP 5 FEET CLEAR OF AIRCRAFT ENGINES AND FUEL TANK AREAS." Tables, racks, trays, and wiring shall not be located within a Class I location and, in addition, shall comply with Article 480. 513-10. External Power Sources for Energizing Aircraft. (a) Not Less than 18 Inches (457 mm) Above Floor. Aircraft energizers shall be so designed and mounted that all electric equipment and fixed wiring will be at least 18 inches (457 mm) above floor level and shall not be operated in a Class I location as defined in Section 513-2(c). (b) Marking for Mobile Units. Mobile energizers shall carry at least one permanently affixed warning sign to read: "WARNING - KEEP 5 FEET CLEAR OF AIRCRAFT ENGINES AND FUEL TANK AREAS." (c) Cords. Flexible cords for aircraft energizers and ground support equipment shall be approved for the type of service and extra-hard usage and shall include an equipment grounding conductor. 513-11. Mobile Servicing Equipment with Electric Components. (a) General. Mobile servicing equipment (such as vacuum cleaners, air compressors, air movers, etc.) having electric wiring and equipment not suitable for Class I, Division 2 locations shall be so designed and mounted that all such fixed wiring and equipment will be at least 18 inches (457 mm) above the floor. Such mobile equipment shall not be operated within the Class I location defined in Section 513-2(c) and shall carry at least one per-