The basics of device circuit breakers | Challenges in applications
6
Challenges in applications
The demands of normal system operation in no way represent a challenge when selecting device circuit breakers . What is more difficult is taking the starting behavior of the various loads into consideration . This is because the starting behavior frequently varies greatly , often causing a multiple of the current to flow ( Fig . 23 and 24 ). This situation must not result in a shutdown . This has to be taken into consideration both in the choice of device circuit breaker as well as the right power supply , the same as a potential fault . The power supply must have sufficient reserve for this .
t / s |
1000 |
t / s |
1000 |
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100 |
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100 |
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10 |
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10 |
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1 |
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1 |
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0,1 |
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0,1 |
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0,01 |
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0,01 |
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0,001 |
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0,001 |
0,0001 |
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0 |
5 |
10 |
15 |
20 |
25 |
30 |
35 |
40 |
45 |
50 |
2 A halogen lamp starting current |
I / A |
Tripping curve for 4 A thermomagnetic circuit breaker |
Power supply unit power reserve |
0,0001 |
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0 |
5 |
10 |
15 |
20 |
25 |
30 |
35 |
40 |
45 |
50 |
2 A halogen lamp starting current |
I / A |
4 A CBMC tripping curve |
Power supply unit power reserve |
Fig . 23 : A 4 A thermomagnetic circuit breaker indeed acts slowly enough to start the halogen lamp , but the power supply must also have a lot of reserve power ready .
Fig . 24 : Thanks to intelligent short-circuit and starting current detection , electronic circuit breakers can shut down more accurately under identical conditions . This means that a much smaller reserve is needed than with comparable thermomagnetic device circuit breakers ( cf . Fig . 23 ).
DC motor startup behavior Nominal current
500 mA Starting current / time 2 x In = 1 A / approx . 500 ms
8 x In = 4 A / approx . 50 ms
Fan startup behavior Nominal current Starting current / time
500 mA 2 x In = 1 A / approx . 500 ms 3 x In = 1.5 A / approx . 100 ms
PhoENix CoNtACt 23