The choice of a CB is made in terms of: 1. Electrical characteristics (AC or DC, Voltage. ) of the installation for which the CB is intended 2. Its environment: ambient temperature, in a kiosk or switchboard enclosure, climatic conditions, etc. 3. Presumed short-circuit current at the point of installation 4.. .
The rated current of a circuit breaker is defined for operation at a given ambient temperature, in general: 1. 30°C for domestic-type CBs according to IEC 60898. .
Circuit-breakers with uncompensated thermal tripping elements have a tripping-current level that depends on the surrounding temperature. If the CB is installed in. .
These tripping units include a bi-metal compensating strip which allows the overload trip-current setting (Ir or Irth) to be adjusted, within a specified range,. .
An important advantage with electronic tripping units is their stable performance in changing temperature conditions. However, the switchgear itself often imposes. The choice of a CB is made in terms of: Characteristics of the protected cables, busbars, busbar trunking system and application (distribution, motor. ) Co-ordination with upstream and/or downstream device: selectivity, cascading, coordination with switch disconnector, contactor.
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