Fluke 179 Fluke Multimeters - ABCs of Multimeter Safety Multimeter Safety and
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- Fluke 179 | Fluke Multimeters - ABCs of Multimeter Safety Multimeter Safety and - Page 1
to do with misuse-it was a momentary high-voltage spike or transient that hit the multimeter input without warning. 189 TRUE RMS MULTIMETER TEMPERATURE A mA A COM V 10A MAX FUSED 400mA FUSED CAT 1000V Voltage spikes-an unavoidable hazard As distribution systems and loads become more complex - Fluke 179 | Fluke Multimeters - ABCs of Multimeter Safety Multimeter Safety and - Page 2
can deliver large currents. If a transient causes an arc-over, the high current can sustain the arc meters, primary overcurrent protection equipment. • Outside and service entrance, service drop from pole to building, run between meter V) test equipment. Fluke Corporation ABCs of multimeter safety - Fluke 179 | Fluke Multimeters - ABCs of Multimeter Safety Multimeter Safety and - Page 3
. 3. Make sure you're grounded (through your hand, to the floor), to complete the capacitive voltage connection. Use either a voltage detector "wand" or a DMM with non-contact measurement built in. This meter has a built-in non-contact voltage tester. ABCs of multimeter safety Fluke Corporation - Fluke 179 | Fluke Multimeters - ABCs of Multimeter Safety Multimeter Safety and - Page 4
. When the arc forms inside the meter, a very high-pressure shock wave can cause a loud bang!-very much like a gunshot or the backfire from a car. At the same instant, the tech sees bright blue arc flashes at the test lead tips-the fault currents superheat the probe tips, which start to burn away - Fluke 179 | Fluke Multimeters - ABCs of Multimeter Safety Multimeter Safety and - Page 5
Arc blast and electric shock Use the right high-energy fuses TEMPERA A mA A COM V 189 TRUE RMS MULTIMETER V TEMPERATURE AA COM mA A COM V 10A MAX FUSED 400mA FUSED CAT 1000V Figure 3. Misuse of DMM in Ammeter Mode. Transients aren't the only source of possible short circuits and arc - Fluke 179 | Fluke Multimeters - ABCs of Multimeter Safety Multimeter Safety and - Page 6
. What is realistic, and highly recommended, is to select a multi meter rated to the highest category in which it could possibly be used. In other words, err on the side of safety. Fluke Corporation ABCs of multimeter safety Use protective equipment such as safety glasses and insulated gloves. - Fluke 179 | Fluke Multimeters - ABCs of Multimeter Safety Multimeter Safety and - Page 7
voltage and source impedance. These three criteria together will tell you a multimeter's true voltage withstand value. Measurement Category Working Voltage (dc or ac-rms to ground) Peak Impulse Transient (20 repetitions) Test Source (Ω = V/A) CAT I 600 V 2500 V 30 Ohm source CAT I 1000
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ABCs of
multimeter safety
Multimeter safety and you
Voltage spikes–an
unavoidable hazard
As distribution systems and
loads become more complex,
the possibilities of transient
overvoltages increase. Motors,
capacitors and power conver-
sion equipment such as vari-
able speed drives can be prime
generators of spikes. Lightning
strikes on outdoor transmission
lines also cause extremely haz-
ardous high-energy transients.
If you’re taking measurements
on electrical systems, these
transients are “invisible” and
largely unavoidable hazards.
They occur regularly on low-
voltage power circuits, and can
reach peak values in the many
thousands of volts. In these
cases, you’re dependent for pro-
tection on the safety margin
already built into your meter.
The voltage rating alone will
not tell you how well that meter
was designed to survive high
transient impulses.
Early clues about the safety
hazard posed by spikes came
from applications involving
measurements on the supply
bus of electric commuter rail-
roads. The nominal bus voltage
was only 600 V, but multi-me-
ters rated at 1000 V lasted only
a few minutes when taking
measurements while the train
was operating. A close look re-
vealed that the train stopping
and starting generated 10,000 V
spikes. These transients had
no mercy on early multime-
ter input circuits. The lessons
learned through this investiga-
tion led to significant improve-
ments in multimeter input
protection circuits.
New safety standards
To protect you against tran-
sients, safety must be built into
the test equipment. What per-
formance specification should
you look for, especially if you
know that you could be work-
ing on high-energy circuits?
The task of defining new safety
standards for test equipment
was recently addressed by
the IEC (International Electro-
technical Commission). This
organization develops interna-
tional safety standards for
electrical test equipment.
For a number of years the in-
dustry used IEC 348 in design-
ing equipment. That standard
has been replaced by IEC 1010.
While well-designed IEC 348
meters have been used for years
by technicians and electricians,
the fact is that meters designed
to the new IEC 1010 standard
offer a significantly higher level
of safety. Let’s see how this is
accomplished.
A
mA
COM
V
TEMPERATURE
A
TRUE RMS MULTIMETER
189
400mA
FUSED
10A MAX
FUSED
CAT
1000V
Application Note
From the Fluke Digital Library @ www.fluke.com/library
Don’t overlook safety–
your life may depend on it
Where safety is a concern,
choosing a multimeter is like
choosing a motorcycle helmet–
if you have a “ten-dollar” head,
choose a “ten-dollar” helmet. If
you value your head, get a safe
helmet. The hazards of motor-
cycle riding are obvious, but
what’s the issue with multime-
ters? As long as you choose a
multimeter with a high-enough
voltage rating, aren’t you safe?
Voltage is
voltage, isn’t it?
Not exactly. Engineers who
analyze multimeter safety often
discover that failed units were
subjected to a much higher
voltage than the user thought
he was measuring. There are
the occasional accidents when
the meter, rated for low voltage
(1000 V or less), was used to
measure medium voltage, such
as 4160 V. Just as common, the
knock-out blow had nothing to
do with misuse–it was a mo-
mentary
high-voltage spike or
transient
that hit the multimeter
input without warning.