Description
2.3 Technical details
3VA molded case circuit breakers with IEC certificate
Manual, 03/2019, A5E03603177010-03
49
2.3.5
Current limitation
"Current limiting" means that the peak value of the prospective impulse short-circuit current i
p
is limited to a smaller let-through current i
D
.
The compact design of the breakers has been made possible by their excellent current
limiting capabilities. In the event of a short-circuit, the molded case circuit breaker
substantially reduces the magnitude of the let-through currents, i.e. reduces the load
reaching downstream equipment (less thermal load, lower dynamic forces). The level of let-
through energy is also reduced to a considerable extent.
3VA molded case circuit breakers are designed with a current-limiting capability.
IEC EN 60947-2 (VDE 0660-101), section 2.3, page 12, defines current-limiting molded case
circuit breakers as follows:
"Circuit breaker that, within a specified range of current, prevents the let-through current from
reaching the prospective peak value and which limits the let-through energy (I
2
t) to a value
less than the let-through energy of a half-cycle wave of the symmetrical prospective current."
①
Unlimited current
②
Peak value of limited current
③
Limited current
i
D
Let-through current
i
p
Unlimited impulse short-circuit current
t
a
Break time
