AQB-LF250 (fig. 2-36), combines the standard AQB
circuit breaker and a current-limiting fuse unit. This
fuse unit interrupts the circuit when the current is in
excess of the interrupting rating of the breaker.
Constructed as one compact unit, the AQB-LF circuit
breaker incorporates the current-limiting fuses (fig.
2-37) as integral parts of the circuit breaker. The
common trip features and trip units in this type of
circuit breaker are identical to those in the AQB-A250
The current-limiting fuse unit is designed so that
it trips the breaker and opens all poles if any
current-limiting fuse (fig. 2-38) is blown. After a fuse
has blown, the circuit breaker cannot be reclosed until
the blown fuse is replaced. Any attempt to remove the
fuse unit when the circuit breaker is in the closed
position will automatically trip the breaker.
The AQB-LF250 circuit breaker is inter-
changeable with the AQB-250 circuit breaker, except
a larger cutout is required in the switchboard front
panel to accommodate the fuse unit of the
Figure 2-36.-Type AQB-LF250 complete circuit breaker,
Figure 2-37.--Type AQB-LF250 complete circuit breaker, front view with fuse unit removed.