S&C Instruction Sheet 662-510
23
Re-Fusing
How to Detect and Replace
a Blown Fuse
Open the appropriate fuse-compartment door and secure
it with the door holder. On double-door models, the adja-
cent door should be closed and latched to minimize expo-
sure to high voltage. Also remove the dual-purpose front
barrier (using the Grappler tool) or inner barrier panel,
if fur nished.
S&C Power Fuses
From a safe distance, observe the blown-fuse target for
the fuse type furnished. Refer to Figure 28:
•
SML-4Z Power Fuse
—A fl uorescent-orange target in
the translucent SML-4Z Holder moves to the BLOWN
indicator window when the fuse operates, permitting a
positive visual check of fuse condition without remov-
ing the fuse from its mounting. The target fl uoresces
when illuminated.
•
SML-20 Power Fuse or Fault Fiter Electronic
Power Fuse
—A red blown-fuse target projects from
the top of the SML-20 Power Fuse upper end-fi tting or
the Fault Fiter Holder when the fuse has operated . . .
making it easy to check fuse condition with the fuse
in the
Closed
position. The blown-fuse target retracts
within the end-fi tting or holder when the blown fuse
unit or interrupt ing module is replaced.
Note On Handling:
The present-design upper end-fitting
for use in SML-20 Power Fuses and the Fault Fiter Holder
use a free-floating blown-fuse target that can move
(by force of gravity) into the
Blown
position should the
fuse be inverted during handling. The fuse condition
can be veri fied by returning the fuse to the upright posi-
tion. If the fuse is blown, the target will remain in the
extended (projecting) position.
Remove the blown fuse from its mounting following
the instructions found in the “Opening and Removing
the Fuse” section on pages 20 through 22. Then, follow
the instruc tions for replacing blown SM-4 Refill Units,
SMU-20 Fuse Units, or Fault Fiter Interrupting Modules
(as applicable) provided with each new refill unit, fuse
unit, and interrupting module.
Current-Limiting Fuses
To fi nd the blown fuse(s), remove each fuse in turn from
its mounting (the target cannot be seen while the fuse is
in its mounting), following the instructions found in the
“Opening and Removing the Fuse” section on pages 20
through 22. Then, inspect the fuse and check for a blown-
fuse target.
Note:
Following a two- or three-phase fault at a three-
phase installation, any unblown fuses that carried the
fault current should also be replaced. For instructions
on replacing current-limiting fuses in S&C Holders,
refer to S&C Instruction Sheet 660-500. S&C Holders
will accommodate the current-limiting fuses listed in
Appendix D starting on page 31.
Installing the Fuse in the Mounting
Follow the instructions found in the “Installing and
Clos ing the Fuse” section on pages 16 through 18.
Figure 28. Blown-fuse target locations for the fuse types used in PMH models of S&C Pad-Mounted Gear.
Fault Fiter Electronic Power Fuse
Red target projects from
top of holder when fuse
has operated
Fluorescent-orange target appears
in
the BLOWN indicator window
when fuse has operated (visible
through translucent holder)
SML-4Z Power Fuse
Red target projects
from top of holder when
fuse has operated
SML-20 Power Fuse
