Application Note

7 Fluke Corporation ABCs of multimeter safety
Understanding voltage
withstand ratings
IEC 61010-1 test procedures
take into account three main
criteria: steady-state voltage,
peak impulse transient voltage
and source impedance. These
three criteria together will tell
you a multimeter’s true voltage
withstand value.
When is 600 V more than
1000 V?
Table 2 can help us understand
an instrument’s true voltage
withstand rating:
1. Within a category, a higher
“working voltage” (steady-
state voltage) is associated
with a higher transient,
as would be expected. For
example, a CAT III-600 V
meter is tested with 6000 V
transients while a CAT III-
1000 V meter is tested with
8000 V transients. So far, so
good.
2. What is not as obvious is the
difference between 6000 V
transient for CAT III-600 V
and the 6000 V transient for
CAT II-1000 V. They are not
the same. This is where the
source impedance comes in.
Ohm’s Law (Amps = Volts/
Ohms) tells us that the 2 W
test source for CAT III has six
times the current of the 12 W
test source for CAT II.
The CAT III-600 V meter clearly
offers superior transient pro-
tection compared to the CAT
II-1000 V meter, even though its
so-called “voltage rating” could
be perceived as being lower.
It is the combination of the
steady-state voltage (called the
working voltage), and the cat-
egory that determines the total
voltage withstand rating of the
test instrument, including the
all-important transient voltage
withstand rating.
A note on CAT IV: Test
values and design standards for
How to evaluate a multimeter’s safety rating
Category IV voltage testing are
addressed in IEC IEC 61010-1
standard.
Creepage and clearance
In addition to being tested to
an actual overvoltage tran-
sient value, multimeters are
required by IEC IEC 61010-1 to
have minimum “creepage” and
“clearance” distances between
internal components and circuit
nodes. Creepage measures
distance across a surface.
Clearance measures distances
through the air. The higher the
category and working voltage
level, the greater the internal
spacing requirements.
The bottom line
If you are faced with the task of
replacing your multimeter, do
one simple task before you start
shopping: Analyze the worst-
case scenario of your job and
determine what category your
use or application fits into.
First choose a meter rated
for the highest category you
could be working in. Then,
look for a multimeter with a
voltage rating for that category
matching your needs. While
you’re at it, don’t forget the test
leads. IEC 61010-1 applies to
test leads too: they should be
certified to a category and volt-
age as high or higher than the
meter. When it comes to your
personal protection, don’t let
test leads be the weak link.
Look for category and voltage ratings of test leads and multimeters.
Working Voltage Peak Impulse
Measurement (dc or ac-rms Transient Test Source
Category to ground) (20 repetitions) (W = V/A)
CAT 0 600 V 2500 V 30 Ohm source
CAT 0 1000 V 4000 V 30 Ohm source
CAT II 600 V 4000 V 12 Ohm source
CAT II 1000 V 6000 V 12 Ohm source
CAT III 600 V 6000 V 2 Ohm source
CAT III 1000 V 8000 V 2 Ohm source
CAT IV 600 V 8000 V 2 Ohm source
Table 2: Transient test values for measurement categories. (50 V/150 V/300 V
values not included.)
Fluke Corporation
PO Box 9090, Everett, WA 98206 U.S.A.
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
In the U.S.A. [phone] or
Fax [phone]
In Europe/M-East/Africa [phone] or
Fax [phone]
In Canada (800)-36-FLUKE or
Fax [phone]
From other countries [phone] or
Fax [phone]
Web access: http://www.fluke.com
©2006-2014 Fluke Corporation.
Specifications subject to change without notice.
Printed in U.S.A. 10/2012 1263690J_EN
Modification of this document is not permitted
without written permission from Fluke Corporation.
Fluke. The Most Trusted Tools
in the World.