Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 71)

- EN Æ EEx e IIC T6
- IEC
Æ Ex e IIC T6
For the following considerations the ignition protection type Increased Safety “e” for motors in
conjunction with the associated motor protection is of primary interest. It should thereby be
noted that the motor protective devices should be installed outside the hazardous areas. This
application option is specially identified under CENELEC (see Section
2.4.7.5 ). With this ignition
protection type, special precautions are taken to ensure an increased margin of safety and to
avoid the occurrence of impermissibly high surface temperatures and of sparks or electric arcs
inside or outside the electrical equipment.
2.4.7.3 Motors for hazardous areas
Electrical drives that are operated in hazardous areas must be built and engineered so that they
cannot become an ignition source. This applies not only to normal operating and starting, but
also in case of faults, for example at stalled rotor.
The specified temperature limits for hot surfaces as a potential source of ignition have for
ignition protection types Flameproof enclosures “d” (transfer of an explosion to the outside
excluded) and Pressurized enclosures “p” (Ex-atmosphere is kept away from the source of
ignition) to be complied with only on the outside of the enclosure. Due to the lag in temperature
changes of the motor housing, short-term temperature rise of the windings over the limit
temperature of the temperature class are with these ignition protection types regarded as non-
critical from an explosion protection viewpoint. In contrast, with a motor of ignition protection
type Increased Safety “e” (suppression of sparks and high temperatures), exceeding the limit
temperature of the corresponding temperature class, for which the motor is foreseen, inside the
motor even short-term is not permissible.
Limit temperatures (°C)
Temperature class T1 T2 T3 T4 T5 T6
Ignition class
IEC/EN 60079-14, Tab.1
> 450 300 200 135 100 85
Maximum surface temperature
EN 50014. Tab.1; IEC/EN 60079-14 Tab.1
< 450 300 200 135 100 85
Windings class F continuously
EEx e, EN 50019, Tab. 3
< 130 130 130 130 95 80
Winding class F at end of t
E
EN 50019, Tab. 3
< 210 210 195 130 95 80
= determined by the temperature class of the gas
= determined by the temperature class (isolation class) of the windings
Tab. 2.4-4
Limit temperatures of electrical machines of ignition protection type “e” with insulation material class F.
IEC 60079-14 ed. 4.0. Copyright © IEC, Geneva, Switzerland. www.iec.ch
Based on the requirement that premature damage and ageing of the motor windings must be
reliably prevented, there is a further limitation with respect to the heating characteristic of the
windings: The permissible ultimate temperature rise corresponding to the insulation material
class (temperature class) of the windings is reduced compared to the normal values by
10 to 15 K in motors of ignition protection type “e”. In theory this signifies a doubling of the
windings life span and serves to increase safety, also resulting however in a reduction of the
power output compared with the standard values for a motor of the same size.
The permissible limit temperature of a winding in an electrical machine of ignition protection type
Increased Safety “e” depends, on the one hand, on the temperature class from the explosion
protection viewpoint and, on the other, on the insulation material class of the winding.
Tab. 2.4-4
shows the relevant limit values for motors of isolation class F.
If another insulation material is used, these values change according to the temperature class of
the insulation material (
Tab. 2.4-5 ).
LVSAM-WP001A-EN-P - April 2009 2-43