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Current-Limiting NX® Fuse Guard Tool
Operating instructiOns
MN132015EN November 2016
General
The NX
®
Fault Guard tool is a device that allows temporary
connection of a current-limiting fuse in series with a load
while it is being energized. The tool will limit the available
energy to the load in case of a fault thus minimizing the
expulsion blast and protecting the lineman in case of
catastrophic transformer failure.
The Fault Guard tool with the self-retracting electrical cable
is for use with distribution transformers protected by open-
fuse cutouts. The companion model, equipped with a metal
stirrup, is for use with self-protected transformers.
Application
1. Check the fuse size in the tool against the schedule
that relates transformer kVA to fuse sizes.
2. Make sure that the actuator is intact (see Figure 2).
The actuator can be seen through the opening in the
lower end of the tool. The actuator is the small phenolic
cylinder that protrudes from the bottom of the fuse. An
expended fuse will have a broken actuator.
3. Using either a universal-type or shotgun-type
switchstick, hook the lifting eye of the tool. Raise the
tool to the line and hang it by the hotline clamp (see
Figure 3).
4. Hook the open-fuse cutout pullring (or connect the
hotline clamp from the transformer bushing lead to
the stirrup on the lower-end fitting of the tool) (see
Figure 4).
WARNING
“Fuzzing” at the cutout pullring (or clamp/stirrup
connection) and non-operation of the current-limiting
fuse in the tool indicates that no fault is present and
the circuit may be safely energized (see Figure 5) . The
lack of fuzzing can indicate either a faulted load or an
open fuse in the tool . IF THERE IS NO FUZZING, DO NOT
ENERGIZE THE CIRCUIT!
5. If a fault is present, the current-limiting fuse in the
tool operates as indicated by a small report from the
actuator resembling that of a low-caliber firearm. A
visual verification of actuator operation can also be
made (Step 2).
6. After the fault is cleared and the expended fuse in the
Fault Guard tool is replaced, retest the circuit following
Step 1 through Step 5.
7. If there is no indication of a fault, close the cutout and
unhook the pullring (or remove the hotline clamp from
the transformer bushing lead to the stirrup of the tool),
and then remove the tool from the line (see Figure 6).
Figure 1 . NX Fault Guard tool for use with self-protected
transformers (left) . NX Fault Guard tool for use with
openfuse protected transformers (right) .
Figure 2 . Actuator intact .
