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Siemens AG
Entry type: FAQ Entry ID: 22722332, Entry date: 03/01/2006
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Why variable overload tripping time settings in circuit breakers?

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QUESTION:

For what reasons do circuit breakers require variable overload tripping time settings?

ANSWER:

Tripping characteristic of circuit breakers for motor, generator or line protection shall apply to the thermal load capacity curve of the device to be protected.
Energizing inductive loads like transformers or motors should not result into unsolicitated early tripping.
Another demand is time discrimination.

To avoid a numerous amount of different tripping specifications for the breakers the overcurrent releases have been designed with variable tripping currents and with either fixed or variable tripping times according to different applications.
This provides an optimum of adaptivity to almost every specific protection task.

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