QOU Miniature Circuit Breakers and Switches
Application Information
Interrupting Rating (AIR) at 400 Hz.
At frequencies above 60 Hz, the interrupting rating of thermal-magnetic circuit breakers is less than the
60 Hz interrupting rating. Unless specifically marked for use of 400 Hz systems, the interrupting rating
of Square D circuit breakers is reduced to 1/10th of the 60 Hz interrupting rating.
Magnetic Tripping Performance
At frequencies above 60 Hz more current is necessary to magnetically trip a circuit breaker than at 60
Hz. Fig. 3 shows the multipliers of 60 Hz current that it takes to instantaneously trip a circuit breaker
when applied at various frequencies. For example, at 60 Hz, it takes 700 A or more to magnetically trip
a 100 A QOU circuit breaker per trip curve 730-7 (page 26). At 400 Hz, it takes 1820 A (2.6 multiplier)
or more to magnetically trip the same circuit breaker.
Figure 5: 60 Hz Current Multiplier
20
15
10
9
8
7
6
5
4
3
2
1.5
1
Line Frequency in Hertz
09/2005
11
© 2005 Schneider Electric All Rights Reserved