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05/11 MN03407008Z-DE/EN
Monitoring overload of
motors in the Ex e area
Setup of the overcurrent
protection system
2
Configuration
The "Ex e" degree of protection for motors is achieved by
means of special constructive measures. The motors are
assigned to temperature classes based on the maximum
permitted surface temperatures. The temperature rise time t
and the ratio between the startup current and rated current
I
/I
are calculated in addition and specified on the rating
A
N
plate of the motor.
The temperature rise time t
temperature of the motor winding to rise from the final rated
operational temperature up to the limit temperature, at a
startup current of I
.
A
However, since Ex e motors are not intrinsically safe,
explosion safety can only 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.
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
device must be rated in such a way, so as to ensure that
the tripping time t
A
not higher than its temperature rise time t
its characteristics curve, in order to safely switch off the
motor within that period (a following example).
represents the it takes the
E
. This means, that the protective
E
for the ratio I
/I
of the Ex e motor is
A
N
E
, according to
E
47
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