Fluke 179 Fluke Current Clamp Meters - You Can Guess Which Fuse is Bad or You
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- Fluke 179 | Fluke Current Clamp Meters - You Can Guess Which Fuse is Bad or You - Page 1
be used to test if overloading caused a fuse to open. Use a Fluke 337 with a min/max function, or a 180 Series DMM in min/max mode with a clamp accessory. Leave the clamp attached for a normal load cycle. You will be able to capture the worst-case load on the circuit. From the Fluke Digital Library - Fluke 179 | Fluke Current Clamp Meters - You Can Guess Which Fuse is Bad or You - Page 2
ohms function of measurement: Connect a DMM or clamp meter to one probe to the line side check them. Read across of phase A. Test for fuses on each individual fuse 2 675 200 or Fax (31 40) 2 675 222 In Canada (800)-36-FLUKE or Fax (905) 890-6866 From other countries +1 (425) 446-5500 or
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Application Note
You’ve got a bad fuse in your
three-phase disconnect or
combination motor starter.
With several to pick from, how
do you know which one is
the culprit? Use these simple
troubleshooting methods to
find out quickly.
Ideally circuits should be
de-energized to replace a fuse,
but initial troubleshooting is
sometimes done on live circuits.
Remember, always wear the
appropriate personal safety
gear.
The first step is to open
the panel and visually inspect
it for arcing or burning – good
indications of a phase-to-
ground fault that is popping
the fuse. A damaged enclosure
or component will require
replacement.
You can guess
which fuse is bad…
or you can try this
From the Fluke Digital Library @ www.fluke.com/library
The first step, after opening
the enclosure, is always to test
the line side voltage, which
should be hot.
After that, one of
several methods can be used to
isolate a bad fuse:
•
Current measurement:
Use a clamp to read the
current on each phase: the
phase with an open fuse will
have zero current.
Of course
this assumes that normal
loads are still running on
the good phases.
On three-
phase induction motors, this
method is particularly useful.
That’s because a three-phase
induction motor will continue
to run even if one of the
phases is dead (unless
control circuit power is
drawn from that phase, in
which case the motor starter
will trip).
Eventually, the
motor will overheat and the
overloads should trip.
The
condition is called single-
phasing.
A clamp can easily
spot the open phase.
Of course, there is still
the question of why the fuse
opened. A clamp can also
be used to test if overloading
caused a fuse to open. Use
a
Fluke 337 with a min/max
function, or a 180 Series
DMM in min/max mode with
a clamp accessory.
Leave the
clamp attached for a normal
load cycle. You will be able
to capture the worst-case
load on the circuit.
Checking Fuses
L1
L2
Line
Load
L3
Test Point 1
480 V
L1
L2
Line
Load
L3
Test Point 2
480 V
L1
L2
Line
Load
L3
Test Point 3
480 V
L1
L2
Line
Load
L3
Test Point 4
480 V
Line
Test Point 5
L1
L2
Line
Load
L3
Test Point 6
A
B
C
A
B
C
A
B
C
A
B
C
480 V three-phase system – one bad fuse
L1
L2
Load
L3
Open
Fuse
0 V
A
B
C
A
B
C
480 V
Verify voltage
is present
Find the
bad fuse