(b) Cooling. Electrical equipment that depends on the natural
circulation of air and convection principles for cooling of exposed
surfaces shall be installed so that room airflow over such surfaces is
not prevented by walls or by adjacent installed equipment. For
equipment designed for floor mounting, clearance between top
surfaces and adjacent surfaces shall be provided to dissipate rising
warm air.
Electrical equipment provided with ventilating openings shall be
installed so that walls or other obstructions do not prevent the free
circulation of air through the equipment.