Protection Types for Gas Protection

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

The goal of protection is to prevent one 'source' which can create the explosion. The technical solution is dependent on the standard which fulfils the EHSRs of ATEX Directive according to the category of equipment.

Protection type " p " prevents presence of explosive atmosphere inside the motor		Protection types " e " and " n " prevent ignition source from the motor
	Protection type " d " prevents transmission of explosion outside the motor

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Protection type	Protection is based on
Flameproof enclosure 'd'	- No risks of explosion transmission form inside the motor - No dangerous hot surface or sparks on the outside of the enclosure at rated operation
Pressurised 'p'	- An enclosure which is flushed and pressurised by a protective gas - No dangerous hot surface or sparks on the outside of the enclosure at rated operation
Increased safety 'e'	- No dangerous hot surface or sparks at rated operation, at start or by fault conditions
Non-sparking 'n'	- No dangerous hot surface or sparks at rated operation
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Temperature class
An Ex product should be marked with the corresponding temperature class. The temperature class corresponds to the maximum surface temperature of the product.
According to the type of protection used, the temperature is corresponding either to maximum temperature of external surface or to maximum temperature of internal product.

In all cases the temperature should be below the minimum ignition temperature of the explosive atmosphere in which the product is installed. The margin between the minimum ignition temperature and the temperature marked on the product is under the responsibility of the users.

Temperature class	T1	T2	T3	T4	T5	T6
Temperature °C	450	300	200	135	100	85

General features for design of motors for gas 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 IP55 protection
• 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 if peripheral speed of fan is equal or more than 50 m/s for gas environment
• The fan, fan cover or ventilation screen should not contain mass of more than 6% 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 or internal 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 nominal voltage if the motor is stamped according to IEC 60034-1
  • +/- 10% of nominal voltage if the motor is stamped according to IEC 60038 (or IEC 60079-0)
  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.