Siemens SENTRON 3VL System Manual page 79

Thermomagnetic overcurrent trip unit
Thermomagnetic overcurrent trip units are calibrated to 50 °C. As a result, the tripping times
of the thermal overcurrent trip unit increase for a constant current at low temperatures.
To correct the tripping times, the thermal overcurrent trip unit settings must be changed by
the factor from the table "Derating factors for thermomagnetic overcurrent trip units" in the
Technical data (lower settings).
Use in networks with different frequencies
If low-voltage switching devices designed for 50 / 60 Hz are to be used at other network
frequencies, the following points must be taken into consideration:
● Thermal effects on the system components
● Switching capacity
● Service life of the contact system
● Tripping characteristics of the overcurrent trip unit
● Behavior of the accessories
Thermal rating of the system components and conductors depending on the network frequency
Circuit breakers designed for alternating current of 50 / 60 Hz can be used at lower
frequencies for at least the same rated currents. However, in contrast to this, the permissible
operating current must be reduced at frequencies higher than 100 Hz to ensure the specified
temperature increase limits are not exceeded.
Circuit breakers for 400 Hz applications are available on request.
Use in 16 2/3 Hz networks
Circuit breakers must be selected according to their DC switching capacities for frequencies
up to 16 2/3 Hz. These values can be found in the relevant table in the Technical data
(Page 157). The rated operational current of the circuit breaker is the same at 16 2/3 Hz and
380/400 V as it is at 50/60 Hz – 3-pole, with two poles used in series. At 16 2/3 Hz and
500 V, all three poles must be used in series.
When used in 50/60 Hz networks, selection can be made in the relevant tables in the
Technical data (Page 157) depending on the ambient temperature, switching capacity, etc.
Influence of temperature and humidity on overcurrent trip units
The relevant reduction in the rated operating current (derating) of the SENTRON VL circuit
breakers is also necessary if the operating temperature of 50 °C or 70 °C is exceeded at a
non-condensing humidity level of 95%.
3VL molded-case circuit breakers
System Manual, 03/2009, 110 0110 - 02 DS 01
Application planning
6.7 Use in harsh environments:
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