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502.128 Ventilating Piping
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Ventilating pipes for motors, generators, or other rotating electrical machinery, or for enclosures for electrical equipment, shall be of metal not less than 0.53 mm (0.021 in.) in thickness or of equally substantial noncombustible material and shall comply with all of the following:
- Lead directly to a source of clean air outside of buildings
- Be screened at the outer ends to prevent the entrance of small animals or birds
- Be protected against physical damage and against rusting or other corrosive influences
Ventilating pipes shall also comply with 502.128(A) and (B).
In Class II, Division 1 locations, ventilating pipes, including their connections to motors or to the dust-ignitionproof enclosures for other equipment, shall be dusttight throughout their length. For metal pipes, seams and joints shall comply with one of the following:
- Be riveted and soldered
- Be bolted and soldered
- Be welded
- Be rendered dusttight by some other equally effective means
In Class II, Division 2 locations, ventilating pipes and their connections shall be sufficiently tight to prevent the entrance of appreciable quantities of dust into the ventilated equipment or enclosure and to prevent the escape of sparks, flame, or burning material that might ignite dust accumulations or combustible material in the vicinity. For metal pipes, lock seams and riveted or welded joints shall be permitted; and tight-fitting slip joints shall be permitted where some flexibility is necessary, as at connections to motors.
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