This protection prevents any explosion transmission of dust because:
- The motor itself is dust ignition proof which means no potentially explosive atmosphere can penetrate inside the motor
- The ingress of dust into the motor is prevented by the IP protection, being either IP65 or IP55.
- The maximum surface temperature outside the motor must not exceed the temperature class for which the motor is certified
- No sparks may occur outside the motor enclosure
In this particular protection, the maintenance is a critical parameter to be considered in the definition of the zone and selection of the motor protection accordingly.
The EHSRs of ATEX Directive must be followed; corresponding to Category 2 if motor is dust tight protected IP6X or to Category 3 if motor is dust protected IP5X:
- Equipment to be used in areas exposed to dust must be designed so that dust deposited on their surface is not ignited.
- The surface temperatures of equipment parts must be kept well below the glow temperature of the deposit dust.
- Equipment must be designed so that the ignition of air/dust mixtures is prevented even in the event of operating faults.
- Equipment must be designed so that air/dust mixtures cannot be ignited by foreseeable ignition sources likely to exist during normal operation
- Equipment, including cable entries must be constructed so that taking into account the size of its particles, dust cannot develop explosive mixture.
To be installed in Zone 21 or in Zone 22 containing conductive dust, motors have to comply with category 2 requirements even though it should be used in Zone 22 with 'normal' non-conductive dust.
To be installed in Zone 22 without conductive dust, motors have to comply with category 3.
No motors are allowed to be installed in Zone 20.