51
06/10 MN03402004Z-DE/EN
2
Engineering
Overload monitoring
of Ex e motors
The Ex e protection of motors is achieved by means of special
design 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 of
the starting current to the rated operational current I
A
/I
N
is
also determined and stated on the motor.
The temperature rise time t
E
is the time in which the
temperature of a winding rises from the final temperature in
normal operation to the limit temperature when a starting
current is present I
A
.
However, e motors are not safe on their own. They only
achieve explosion safety by means of additional measures
that are implemented during the installation, involving
suitable selection and conditions (PTB test regulations) etc.
through the connection with a correctly rated and set
overload protective device.
Setting of the overcurrent
protection device
j
Danger!
The current-dependent protective device must be selected
so that not only the motor current is monitored but also
the blocked motor is switched off within the temperature
rise time t
E
. This means that the protective device must be
rated so that the tripping time t
A
for the I
A
/I
N
ratio of the
Ex e motor, that is specified by the characteristic curve, is
not greater than the temperature rise time t
E
in order to
switch off the motor safely within this time. The tolerance
of the overcurrent release of
g
20 % is to be observed (
a
following example).
Summary of Contents for PKE12 Series
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