Dust Ignition Proof 'D' (EN) or 'DIP/Ex tD' (IEC)

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.

Standards concerned with the protection type 'tD':
EN 61241-1: 2004-06
Electrical apparatus for use in the presence of combustible dust Part 1: Protection by enclosures "tD" based on IEC 61241-1
EN 50281-1-1:1998
Electrical apparatus for use in the presence of combustible dust - Part 1-1: Electrical apparatus protected by enclosures - Construction and testing
EN 50281-1-2:1998
Electrical apparatus for use in the presence of combustible dust - Part 1-2: Electrical apparatus protected by enclosures - Selection, installation and maintenance
IEC 61241-0: 2004-07
Electrical apparatus for use in the presence of combustible dust - Part 0: General requirements
IEC 61241-1: 2004-05
Electrical apparatus for use in the presence of combustible dust - Part 1: Protection by enclosures 'tD'

Selection and installation of product

Equipment category
Minimum protection for equipment
Category 1, zone 21
not applicable
Category 2, zone 21 (conductive dust)
IP 6x
Category 3, zone 22 (non-conductive dust)
IP 5x

Temperature limits:

  • The temperature class of the external surface is determined by measuring the maximum temperature rise in worst condition of voltage supply including the voltage tolerances required according to the standard:
    • +/- 5% of the nominal voltage if the motor is stamped according to IEC 60034-1
    • +/- 10% of the nominal voltage if the motor is stamped according to IEC 60038

in both case with an additional margin of 5 K (T3, T4, T5 and T6) and 10 K (T1 and T2) below the temperature class.

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