Quantcast Figure 2-39.-Type NQB-A250 circuit breaker, front view with cover removed.
 

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The AQB-LF250 circuit breaker is a 250-ampere
This circuit breaker is a quick-make, quick-break
frame size. However, the circuit breaker has an
type. If the operating handle is in the tripped (midway
interrupting rate of 100,000 amperes at 500 volts ac.
between ON and OFF) position, indicating a short
The AQB-A250 circuit breaker has an interrupting
circuit or overload, the operating handle must be
moved to the extreme off position. This automatically
rating of 20,000 amperes at 500 volts ac.
While the AQB-A250 circuit breaker could be
either front or back connected, the AQB-LF250 is
designed for back (drawout type) connection only.
NQB CIRCUIT BREAKER.-- The NQB type of
circuit breaker, such as the NQB-A250 circuit breaker
(fig. 2-39), is similar to the AQB-A250 circuit breaker,
except the NQB-A250 has no automatic tripping
devices. This type of circuit breaker is used for circuit
isolation and manual transfer applications. The
NQB-A250 is still a 250-ampere frame size as the
current-carrying parts of the breaker are capable of
carrying 250 amperes. Technically this circuit breaker
is simply a large on-and-off switch. Some types of
AQB and NQB breakers are provided with electrical
operators mounted on the front of the breaker. These
are geared motor devices for remote operation of the
breaker handle.
ALB CIRCUIT BREAKER.-- The ALB circuit
breaker is a designated low-voltage, automatic circuit
breaker. The continuous duty rating ranges from 5 to
200 amperes at 120 volts ac or dc. The breaker is
provided with a molded enclosure, drawout-type
connectors, and nonremovable and nonadjustable
Figure 2-39.-Type NQB-A250 circuit breaker, front view
thermal trip elements.
with cover removed.
Figure 2-38.-Current-limiting fuse unit assembly for type AQB-LF250 circuit breaker.
2-27

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