NQB.--The NQB-A250 circuit breaker is
Constructed as one compact unit, the AQB-LF
similar to the AQB-A250 circuit breaker, except
circuit breaker includes the current-limiting fuses
the NQB-A250 has no automatic tripping devices.
(fig. 9-15, view B) as integral parts of the CB. The
This CB is used for circuit isolation and manual
trip units and trip features in the AQB-LF circuit
transfer applications. The NQB-A250 is a
breaker are the same as those in the AQB-A250
250-ampere frame size. The current-carrying parts
circuit breakers.
of the breaker are capable of carrying 250
The current-limiting fuse unit is designed to
amperes. Technically, this CB is simply a
trip the breaker and open all poles if any current-
250-ampere on-and-off switch.
limiting fuse (fig. 9-15, view C) blows. After a
fuse blows, the CB cannot be reclosed until the
ALB.--The ALB circuit breakers are
blown fuse is replaced. Any attempt to remove
designated low-voltage, automatic CBs. The
the fuse unit causes the CB to automatically go
continuous duty rating ranges from 5 to 200
to the trip position.
amperes at 120 volts ac or dc. The breaker is
provided with a molded enclosure, drawout type
The AQB-LF250 circuit breaker is mechan-
of connectors, and nonremoveable and non-
ically interchangeable with the AQB-A250 circuit
adjustable thermal/magnetic trip elements.
breaker, except a larger cutout is required in the
This CB is a quick-make, quick-break type.
SWBD front panel to accommodate the fuse unit
After the CB trips, before resetting it, you must
of the AQB-LF250.
place the handle in the OFF position.
The AQB-LF250 circuit breaker is a 250-
ampere frame size. However, the CB has an
NLB.--The NLB circuit breakers are just like
interrupting rate of 100,000 amperes at 500 volts
the ALB circuit breakers, except that they have
ac, 60 Hz. The AQB-A250 circuit breaker has an
no automatic tripping device. They are used only
interrupting rating of 20,000 amperes at 500 volts
as on-off switches.
ac, 60 Hz.
POWER DISTRIBUTION
While the AQB-A250 circuit breaker can be
COMPONENTS
either front or back connected, the AQB-LF250
is designed only for back (drawout type) connec-
Many components of the 60-Hz distribution
tion. It uses the same type of slip connectors and
system are located throughout the ship to
terminal studs as shown in figure 9-14.
Figure 9-16.--Typical 60-Hz vital circuit using the ABT.
9-16
