Page 118 - Electrical Safety of Low Voltage Systems
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TT Grounding System 101
FIGURE 6.6 Time–current characteristic of a thermal magnetic molded case
circuit breaker.
and 400 A, depending on the temperature of its contacts. Such currents
correspond to 12 to 25 times the breaker’s rating (i.e., 16 A in our case).
Hence, I a may be too high to satisfy the condition imposed in Eq. (6.4).
The earth loop impedance, in fact, may limit I G to values below I a and,
therefore, the CB may not defend persons against indirect contact in
TT systems.
The general goal of overcurrent devices is to protect installa-
tions against abnormal currents that would compromise the integrity
