Motor protection types

Motors are directly connected to the machines in the potentially explosive atmosphere. These atmospheres have a defined zone classification, and the zone defines the minimum safety level (category) the motors must comply with. The category defines the permitted motor protection types.

Motors can also be classified by Equipment Protection Levels (EPL) according to the IEC/EN standards. The EPL indicates a motor’s inherent risk of ignition. The purpose of this classification is to make the selection of motors for different zones easier.

For motors, EPL marking is included in the Ex marking, equipment category is included in the CE-marking.

Classification into categories is of particular importance, because all the inspection, maintenance and repair duties of the end user will depend on the category of the product/equipment and not on the zone where it is installed.

Examples of Ex motor protection types.

Flameproof Ex d
Increased safety Ex ec
Increased safety Ex eb
Dust ignition protection Ex t

Flameproof Ex d

Flameproof Ex d requirement options for use with an AC drive

  • The motor has been tested together with the drive for the duty intended and with the protective device provided
  • Or, use direct temperature protection with embedded temperature sensors and with sufficient margin to protect bearings or the rotor. The actions of protective devices used shall cause the motor to be disconnected.

Only external surface temperature needs to be considered for Ex temperature class.

Increased safety Ex ec

Increased safety Ex ec requirement options for use with an AC drive

  • The motor is tested with the drive or a comparable drive
  • Or, the motor’s temperature class is determined by calculation
  • Or, use direct temperature control by embedded temperature sensors. The action of the protective device shall cause the motor to be disconnected. Direct temperature control is not applicable for ABB IEC LV motors.

Surface temperature of any part (inside or outside) may not exceed Ex temperature class limit.


Increased safety Ex eb

Increased safety Ex eb requirements for use with an AC drive

The standard requires the motor* be tested in association with the specific drive and protective device for this duty. A combined heat run test is mandatory.

Surface temperature of any part (inside or outside) may not exceed Ex temperature class limit.

*Required only for induction motors


Dust ignition protection Ex t

Dust ignition protection Ex t requirement options for use with an AC drive

  • The motor has been tested together with the drive for this
    duty and with the protective device provided
  • Or, use direct temperature protection with embedded
    temperature sensors and with sufficient margin to protect
    bearings or the rotor. The action of the protective device
    shall cause the motor to be disconnected.

Only external surface temperature needs to be considered for Ex temperature class.

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