29
04/06 AWB1210-1458D/GB
2
Configuration
Overload monitoring of
EEx e motors
The motors are compliant to EEx e type of protection
through special construction measures. The motors are
assigned to temperature classes on the basis of the highest
permissible surface temperatures. The temperature rise time
t
E
and the ratio between startup current and rated current
I
A
/
I
N
are calculated in addition and specified on the rating
plate of the motor.
The temperature rise time
t
E
represents the time that expires
for the temperature of the motor winding to rise from its final
rated operational temperature up to the limit temperature,
at a startup current of
I
A
.
However, EEx e motors are not intrinsically safe. Explosion
safety can only be achieved by taking additional measures
during installation and by selecting appropriate operating
conditions (PTB testing regulations), e.g. by adding a
correctly rated and set overload protection to the circuit.
Setup of the overcurrent
protection system
Warning!
The selected overload protection system must not only
ensure proper monitoring of the motor current, but also
that the seized motor is switched off within the
temperature rise time
t
E
. This means, that the protective
device must be rated in such a way so as to ensure that the
tripping time
t
A
for the ratio
I
A
/
I
N
of the EEx e motor is not
higher than its temperature rise time
t
E
according to its
characteristics curve, in order to safely switch off the
motor within that period (
a
following example).
