Feature: Components
As Figure 2 shows, circuit breakers with a Z characteristic trip at
two to three times the nominal current and are signifi cantly faster than MCBs with a B characteristic, which trip at three to fi ve times the nominal current, or even a C characteristic, which requires fi ve to ten times the current. With an electronic circuit breaker, the selection of the tripping
characteristic is much more fl exible. As part of our PISA-M series, we off er an “adjustable” version, where the tripping currents and characteristics can be adjusted. T us, the tripping speed can be chosen between a fast (max. 2ms) and a slow (max. 10ms) characteristic. T e current values can be individually set for each of the four
channels, as long as the total current does not exceed 20A. With ECBs, users can respond much more fl exibly to diff erent loads or system expansions.
Tripping mechanism: Thermal and magnetic or electrical? A circuit breaker integrates two types of tripping mechanisms: thermal and magnetic. T e thermal fuse is responsible for tripping the circuit breaker in case of overload. Depending on the current level, tripping can take from a few seconds to 1-2 hours. T e bimetal in the circuit breaker is responsible for the thermal
tripping. When the current in the circuit breaker exceeds the nominal value, the bimetal heats up and deforms, triggering a shutdown. Since the current has the same thermal eff ect on both
DC and AC sides, the thermal tripping works the same under defi ned environmental conditions for both, DC and AC. T e magnetic fuse is responsible for the short-circuit tripping of
the circuit breaker. It is supposed to trip within a few milliseconds in a specifi c tripping range (each tripping characteristic has its own range). T e coil in the circuit breaker is responsible for this. When a very high current fl ows, a strong magnetic fi eld is formed, which trips the switch. Since the peak value of the alternating current determines the
size of the magnetic fi eld, a correction factor for the magnetic tripping must be considered when using a circuit breaker in DC circuits. T is correction factor is √2, or 1.41. An electronic circuit breaker, on the other hand, enables
simpler and more precise tripping of the channels. T e ECB continuously measures the current, and the integrated eFuse reliably and quickly trips at the defi ned current value. T is process works independently of external infl uences, such as ambient temperature, which is a signifi cant advantage over MCBs. An ECB directly contributes to higher system availability. T e tripping current of MCBs is always specifi ed as AC in the
datasheet and must be multiplied by 1.41 to convert to DC values; Figure 5 shows the AC current and the corrected DC current.
Temperature dependence and Rated Diversity Factor As explained with the thermal fuse, the bimetal responsible for tripping is temperature-dependent. T is means the higher the ambient temperature, the more the bimetal heats up and trips
Figure 1: Comparison between MCB and eFuse
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