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Instructional Book IB694C694-03
4-6.4 Fuse Truck Installation and Use
The fuse truck is normally installed in series with a circuit
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 inter-
locking system is always provided which prevents opening
of the fuse truck compartment 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
DSII-FT32 and DSII-FT40 fuse truck fuses are normally pro-
vided 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 cur-
rent limiting fuses up to 3000A maximum can be used on
the DSII-FT32 and up to 4000A maximum on the DSII-FT40.
After the fuse truck has been withdrawn from its compart-
ment, the fuses can be removed by unbolting them from
the conductors on the fuse truck. This is a relatively uncom-
plicated procedure on the DSII-FT40 fuse truck, because
there is sufficient working space within the truck. Since the
DSII-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 pro-
cessed are replaced.
4-6.6 Blown Fuse Indicator
CAUTION
FOR PROTECTION AGAINST SINGLE-PHASING, THE CONTROL
POWER FOR TRIPPING THE CIRCUIT BREAkER MUST BE FROM A
RELIABLE SOURCE.
The same blown fuse indicator is provided on fuse trucks
as previously described on DSLII circuit breakers. However,
since there is no opening mechanism on fuse trucks, it can-
not 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 associated 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.
eaton corporation www.eaton.com
Effective July 2010
49
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