Protection Types for Dust Ignition Protection

Different types of protection can be used to follow the EHSRs of ATEX Directive according to the Zones where the equipment is installed.

The goal of protection is to prevent the motor becoming an eventual source of explosion.

The technical solution is dependent on the EHSRs of the ATEX Directive according to the category of equipment.

Protection type "D" or "DIP" or "Ex tD" prevents presence of explosive dust atmosphere

Protection type	Protection is based on
Dust ignition proof / Ex tD - IP 55	Explosive dust cannot penetrate inside the dust protected motor in sufficient quantity to interfere with active part of the motor No dangerous hot surface or sparks on the outside of the enclosure at rated operation
Dust ignition proof / Ex tD - IP 65	Explosive dust cannot penetrate inside the dust-tight motor No dangerous hot surface or sparks on the outside of the enclosure at rated operation and in certain fault conditions
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Temperature class
The marking temperature corresponds to the temperature class of the motor. For dust ignition protection, this temperature will correspond to the maximum temperature of the external surface of the product.
The users have to use different rules compared to the gas environment for installing a motor in an explosive atmosphere.

The limits below must be followed in all cases according to ATEX directive and IEC standards:

Marking temperature of motor	Dust environment	Ignition temperature	Minimum ignition temperature of potentially explosive atmosphere
T °C (125°C)	Cloud	T°cloud	T°cloud > 3/2 x T°C (190°C)
	Layer up to 5 mm (thickness on the motor)	T°5mm	T°5mm > T°C + 75 K (200°C)
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With a layer above 5 mm, special requirements are needed, please consult the manufacturer.

Standards concerned with the protection type 'DIP / Ex 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 61241-14: 2004-07	Electrical apparatus for use in the presence of combustible dust - Part 14: Selection and installation

General features for design of ABB motors for dust ignition protection types

• Minimum value for clearances and creepage distances according to the latest edition of standards
• Insulating material with the highest class of resistance for tracking
• IP 54 or IP 55 protection for Zone 22 areas with non-conductive dust
• IP 65 for Zone 21 areas and for Zone 22 areas with conductive dust
• Clearance between fan and fan cover must be at least 1% of the maximum diameter of fan with a minimum value of 1 mm and maximum 5 mm
• The insulation resistance of fans, fan cover and ventilation screen should not exceed 1 GOhm what ever the peripheral speed of fan for dust environment
• The fan, fan cover or ventilation screen should not contain mass of more than 7.5% of magnesium
• All surfaces, which can charge electrically, should be earthed or equipotential bonded
• Temperature of the relevant surface for determining the temperature class (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 cases with an additional margin of 5 K
• Prevent hazards arising from static electricity by using material with insulation resistance below 1 GOhm.