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Appliances shall be installed in accordance with the manufacturer's installation instructions. [NFPA 54:]
508.2.1 Edge of Roof Clearance
Appliances shall be installed on a well-drained surface of the roof. At least 6 feet (1829 mm) of clearance shall be available between any part of the appliance and the edge of a roof or similar hazard, or rigidly fixed rails, guards, parapets, or other building structures at least 42 inches (1067 mm) in height shall be provided on the exposed side. [NFPA 54:]
508.2.1.1 Guards and Rails
Guards or rails shall be required where the following exist:
  1. The clearance between the appliance and a roof edge or open end of an equipment platform is less than 6 feet (1829 mm).
  2. The open end of the equipment platform is located more than 30 inches (762 mm) above the roof, floor, or grade below.
Where guards or rails are installed, they shall be constructed so as to prevent the passage of a 21 inch (533 mm) diameter ball, resist the imposed loading conditions, and shall extend not less than 30 inches (762 mm) beyond each side of the equipment or appliance.
Exception: Guards shall not be required where a permanent fall arrest anchorage connector system in accordance with ASSE Z359.1 is installed.
508.2.2 Electrical Power
All appliances requiring an external source of electrical power for its operation shall be provided with the following:
  1. A readily accessible electrical disconnecting means within sight of the appliance that completely deenergizes the appliance.
  2. A 120 V-ac grounding-type receptacle outlet on the roof adjacent to the appliance on the supply side of the disconnect switch. [NFPA 54:]
508.2.3 Platform or Walkway
Where water stands on the roof at the appliance or in the passageways to the appliance, or where the roof is of a design having a water seal, a suitable platform, walkway, or both shall be provided above the water line. Such platform(s) or walkway(s) shall be located adjacent to the appliance and control panels so that the appliance can be safely serviced where water stands on the roof. [NFPA 54:]

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