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Type of protection Ex px / Ex pxe

This protection prevents the presence of explosive atmospheres inside the motor because:

  • The protection of the Ex p motor is based mainly on the pressured and purged enclosure by safe air or inert gas.
  • The enclosure should be purged before starting and must be overpressured all the time during operation.
  • The maximum surface temperature outside the motor must not exceed the temperature class for which the motor is certified.
  • No arcs or sparks occur outside the motor enclosure

The EHSRs of ATEX Directive corresponding to category 2 must be followed.

To be installed in Zone 1, the motor must comply with Category 2 requirements, even though it is used in Zone 2.

This type of protection can be used for electrical and non-electrical equipment.

Motors can be designed:

  • with stator enclosure and terminal box 'p' protected
  • or with stator enclosure 'p' protected and terminal box 'increased safety 'e' protected
Standards concerned with protection type 'p'
EN 60079-0: 2004-03
Electrical apparatus for explosive gas atmospheres. Part 0: General requirements.
EN 60079-2: 2004-06
Electrical apparatus for explosive gas atmospheres - Part 2: Pressurized enclosures ‘p’
EN 50014: June 1997
Electrical apparatus for potentially explosive atmospheres. General requirements.
EN 50016: October 1995
Electrical apparatus for potentially explosive atmospheres Pressurized apparatus ‘p’
IEC 60079-0: 2004-01
Electrical apparatus for explosive gas atmospheres. Part 0: General requirements.
IEC 60079-2: 2001-02
Electrical apparatus for explosive gas atmospheres - Part 2: Pressurized enclosures ‘p’
Standards concerned with the terminal box 'e' protected:
EN 60079-0: 2004-03
Electrical apparatus for explosive gas atmospheres. Part 0: General requirements.
EN 60079-7: 2003-08
Electrical apparatus for explosive gas atmospheres. Part 7: Increased safety 'e'.
EN 50014: June 1997
Electrical apparatus for potentially explosive atmospheres. General requirements
EN 50019: July 2000
Electrical apparatus for potentially explosive atmospheres. Increased safety 'e'.
IEC 60079-0: 2004-01
Electrical apparatus for explosive gas atmospheres. Part 0: General requirements.
IEC 60079-7: 2001-11
Electrical apparatus for explosive gas atmospheres. Part 7: Increased safety 'e'.
Marking
Old EN
IEC / New EN
Stator and terminal box 'p'
EEx p
Ex px or Ex py or Ex pz
Stator 'p' and terminal box 'e'
EEx pe
Ex pxe or Ex pye or Expze

Type px pressurizing; pressurization that reduces the classification within the pressurized enclosure from zone 1 to non-hazardous or group I to non-hazardous.

Type py pressurizing; pressurization that reduces the classification within the pressurized enclosure from zone 1 to zone 2.

Type pz pressurizing; pressurization that reduces the classification within the pressurized enclosure from zone 2 to non-hazardous.

Equipment must be designed and constructed so that it prevents ignition sources arising, even in the event of frequently occurring disturbances or equipment operating faults, which normally have to be taken into account.

Equipment parts must be designed and constructed so that their stated surface temperatures are not exceeded, even in the case of risks arising from abnormal situations anticipated by the manufacturer.

The protection of the Ex p motor is mainly based on the pressured and purged enclosure. The enclosure should be purged before starting and must be overpressured all the time during operation. The overpressure must be at least 50 Pa. If it falls under the trip limit, the electrical supply should be automatically switched off. The purging gas could be normal air, but it must be supplied from the safe area.

Due to overpressure, the inner part of the enclosure does not belong to the hazardous area, so the temperature limits of stator and rotor are the same as for a standard machine. The contributions of single fault condition must still be taken into account (e.g. the pressure can drop, if pressurized air supply from the network is lost). This means that all temperatures of the inner parts should be under T-class limit in normal operating condition.

Ex px protected motor Typical hook-up diagram of Ex px motor
Ex-px-protected-motor
Ex-px-motor-diagram

Accessories
The external accessories must be Ex-certified at least to zone 1 areas.
The internal accessories should also be Ex protected, if these can be switched independently on (e.g. space heater).

Ex nA or Ex e motors with a provision for pre-start purging
Ex nA or Ex e motors can be equipped with a provision for pre-start purging. The pre-start purging means that customer can purge the enclosure before starting to ensure that the enclosure is free of flammable gases. In this case the motor is NOT over-pressured during normal operation.

All Ex p motors must be certified by an authorised laboratory.

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