I.
B.
694C694-02
4-6.4 FUSE TRUCK INSTALLATION AND USE
The fuse truck is normally installed
in
series with a cir-
cuit breaker of the same current rating. When this is
done, the fuse truck should be
in
the circuit ahead of the
circuit breaker
in
order to maximize protection of the
equipment. The fuse truck must never be permitted to
close the current circuit or to open it when levering the
truck
in
or out of the compartment, because the primary
disconnect contacts are not designed for this service.
For this reason, a key interlocking system is always pro-
vided which prevents opening of the fuse truck compart-
ment door unless the associated circuit breaker has
been opened, pulled out and held
in
the DISCONNECT
position. This key interlock is installed on the fuse truck
compartment door, not the fuse truck itself.
4-6.5 FUSE REPLACEMENT
DSll-FT32 and DSll-FT40 fuse truck fuses are normally
provided when the fuse truck is manufactured. The fuse
trucks are interlocked to prevent the use of maximum
current rated fuses other than the Cutler-Hammer truck
fuse. Class L current limiting fuses up to 3000A maxi-
mum can be used on the DSll-FT32 and up to 4000A
maximum on the DSll-FT40.
After the fuse truck has been withdrawn from its com-
partment, the fuses can be removed by unbolting them
from the conductors on the fuse truck. This is a relative-
ly uncomplicated procedure on the DSll-FT40 fuse
truck, because there is sufficient working space within
Effective
07
/97
Page
43
the truck. Since the DSll-FT32 fuse truck is more space
restricted, it is necessary to first remove the front cover,
levering device assembly and bracket (Figure 4-20).
After replacing the fuses, be sure that all connection
bolts are tight and that all truck parts removed during
the processed are replaced.
4-6.6 BLOWN FUSE INDICATOR
A CAUTION
FOR PROTECTION AGAINST SINGLE-PHASING,
THE CONTROL POWER FOR TRIPPING THE CIR-
CUIT BREAKER MUST BE FROM A RELIABLE
SOURCE.
The same blown fuse indicator is provided on fuse
trucks as previously described on DSLll circuit breakers.
However, since there is no opening mechanism on fuse
trucks, it cannot serve directly as an anti-single phase
device. In order to perform this function, the blown fuse
indicator is arranged to mechanically operate a switch,
which is wired to secondary contacts on the fuse truck.
The switchgear assembly wiring must be arranged to
connect this switch into the tripping circuit of the associ-
ated circuit breaker (Figure 4-19). Again, the indicator
must be reset after being operated to reset the switch,
or
its contact will prevent the breaker from being closed.
Courtesy of NationalSwitchgear.com
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