Checking ground
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electrode impedance for
commercial, industrial
and residential buildings
Most facilities have grounded electrical systems, so that in the event of a lightning strike
or utility overvoltage, current will find a safe path to earth. A ground electrode provides
the contact between the electrical system and the earth. To ensure a reliable connection to earth, electrical codes, engineering standards, and local standards often specify
a minimum impedance for the ground electrode. The International Electrical Testing
Association specifies ground electrode testing every three years for a system in good
condition with average up-time requirements. This application note explains earth/ground
principles and safety in more depth and then describes the principle testing methods: 3
and 4 pole Fall-of-Potential testing, selective testing, stakeless testing and 2 pole testing.
Why Ground?
The US National Electrical Code (NEC) gives two
principle reasons for grounding a facility.
• Stabilize the voltage to earth during normal
operation.
• Limit the voltage rise created by lightning,
line surges or unintentional contact with
higher-voltage lines.
Current will always find and travel the leastresistance path back to its source, be that a utility
transformer, a transformer within the facility or a
generator. Lightning, meanwhile, will always find a
way to get to the earth.
In the event of a lighting strike on utility lines
or anywhere in the vicinity of a building, a lowimpedance ground electrode will help carry the
energy into the earth. The grounding and bonding
Figure 1: A grounding system combining reinforcing steel and
a rod electrode
Application Note
systems connect the earth near the building with
the electrical system and building steel. In a lightning strike, the facility will be at approximately the
same potential. By keeping the potential gradient
low, damage is minimized.
If a medium voltage utility line (over 1000 V)
comes in contact with a low voltage line, a
drastic overvoltage could occur for nearby facilities. A low impedance electrode will help limit the
voltage increase at the facility. A low impedance
ground can also provide a return path for utilitygenerated transients.
system for a commercial building.
Ground Electrode Impedance
The impedance from the grounding electrode
to the earth varies depending on two factors: the
resistivity of the surrounding earth and the structure
of the electrode.
Resistivity is a property of any material and it
defines the material’s ability to conduct current.
The resistivity of earth is complicated, because it:
• Depends on composition of the soil (e.g. clay,
gravel and sand)
• Can vary even over small distances due to the
mix of different materials
• Depends on mineral (e.g. salt) content
• Varies with compression and can vary with time
due to settling
• Changes with temperature, freezing (and
thus time of year). Resistivity increases with
decreasing temperature.
• Can be affected by buried metal tanks, pipes,
re-bar, etc.
• Varies with depth
Since resistivity may decrease with depth, one
way to reduce earth impedance is to drive an electrode deeper. Using an array of rods, a conductive
ring or a grid are other common ways of increasing
the effective area of an electrode. Multiple rods
Figure 1 shows a grounding
F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y
should be outside of each other’s “areas of influence” to be most effective (see Figure 2). The rule
of thumb is to separate the elements by more than
their length. For example: 8-foot rods should be
spaced more than 8 feet apart to be most effective.
The NEC specifies 25 ohms as an acceptable limit
for electrode impedance. The IEEE Standard 142
Recommended Practice for Grounding of Industrial
and Commercial Power Systems (“Green Book”)
suggests a resistance between the main grounding electrode and earth of 1 to 5 ohms for large
commercial or industrial systems.
Local authorities including the authority having
jurisdiction (AHJ) and plant managers are responsible for determining acceptable limits for ground
electrode impedance.
Note: Power distribution systems deliver alternating
current and ground testers use alternating current
for testing. So, you’d think we would talk about
impedance, not resistance. However, at power line
frequencies, the resistive component of the earth
impedance is usually much bigger than the reactive
component, so you will see the terms impedance and
resistance used almost interchangeably.
How do ground impedance
testers work?
There are two types of ground impedance testers.
Three and four point ground testers and clamp-on
ground testers. Both types apply a voltage on the
electrode and measure the resulting current.
A three or four-pole ground tester combines
a current source and voltage measurement in a
“lunch box” or multimeter-style package. They use
multiple stakes and/or clamps.
Ground testers have the follwing characteristics:
AC test current. Earth does not conduct dc
•
very well.
Test frequency that is close to, but distinguish-
•
able from the power frequency and its harmonics. This prevents stray currents from interferring
with ground impedance measurements.
Separate source and measure leads to compen-
•
sate for the long leads used in this measurement.
Input filtering designed to pick up its own signal
•
and screen out all others.
Clamp-on ground testers resemble a large clamp
meter. But they are very different because clampon ground testers have both a source transformer
and a measurement transformer. The source
transformer imposes a voltage on the loop under
test and the measurement transformer measures
the resulting current. The clamp-on ground tester
uses advanced filtering to recognize its own signal
and screen out all others.
Figure 2: Ground electrodes have “areas of influence” that
surround them
Ground Testing Safety
Always use insulated gloves, eye protection and
other appropriate personal protective equipment
when making connections. It is not safe to assume
that a ground electrode has zero voltage or zero
amps, for reasons given below.
To perform a basic ground test (called Fall-ofPotential) on an electrode, the electrode must be
disconnected from the building. New selective
methods allow accurate testing with the electrode
still connected. See “Selective Measurements.”
A ground fault in the system might cause significant current to flow through the ground conductor.
You should use a clamp meter to check for current
before performing any impedance testing. If you
measure above 1 amp you should investigate the
source of the current before proceeding.
If you must disconnect an electrode from an
electrical system, try to do so during a maintenance
shutdown when you can de-energize the system.
Otherwise, consider temporarily connecting a
backup electrode to the electrical system during
your test.
Never disconnect a ground electrode if there is a
chance of lightning.
A ground fault in the vicinity can cause voltage
rises in the earth. The source of the ground fault
may not even be in the facility you are testing, but
could cause voltage between the test electrodes.
This can be especially dangerous near utility
substations or transmission lines where significant
ground currents can occur. (Testing grounding
systems of transmission towers or substations
requires the use of special “Live Earth” procedures
and is not covered in this app note.)
Ground impedance testers use much higher
energy than your standard multimeter. They can
output up to 250 mA. Make sure everyone in the
area of the test is aware of this and warn them not
to touch the probes with the instrument activated.
2 Fluke Corporation Checking ground electrode impedance for commercial, industrial and residental buildings.
Checking Connection Resistance
Measured
Resistance
Distance of P2 from E
Current
Spike
Potential
Spike
Electrode
Under test
Electrode/Earth
Impedance
I
V
E
P2
C2
d1 d2
C2
R
H
R
E
P2 C1&P1
V
I
Leading Up to the Electrode
Before testing the electrode, start by checking its
connection to the facility bonding system. Most
Fall-of-Potential testers have the ability to measure
2-pole, low ohms and are perfect for the job. You
should see less than 1 ohm:
At the main bonding jumper
•
Between the main bonding jumper and the
•
ground electrode conductor
Between the ground electrode conductor and
•
the ground electrode
Along any other intermediate connection
•
between the main bonding jumper and the
ground electrode
The Fall-of-Potential Method
The Fall-of-Potential method is the “traditional”
method for testing electrode resistance. The procedure is specified in the IEEE-81 standard “Guide for
Measuring Earth Resistivity, Ground Impedance and
Earth Surface Potentials of a Ground System.” In it’s
basic form, it works well for small electrode systems
like one or two ground rods. We will also describe
the Tagg Slope Technique which can help you draw
accurate conclusions about larger systems.
Remember: for this method, the ground electrode must be disconnected from the building
electrical service.
The tricky part comes in determining where to
drive the stakes to get a true reading of the resistance between the electrode and the earth.
At what point does the dirt surrounding the
electrode stop being a contributor of resistance
and become the vast earth? Remember that we
are not interested in the resistance between the
electrode and our stakes. We are trying to measure
the resistance that a fault current would see as it
passes through the mass of the earth.
The current probe generates a voltage between
itself and the electrode under test. Close to the
electrode, the voltage is low and becomes zero
when the P stake and electrode are in contact.
How it works
The Fall-of-Potential method connects to the
Figure 3: 3-point measurement
earth at three places. It is often called the “threepole method.” You may want to use a fourth lead
for precise measurements on low-impedance
electrodes, but for our initial discussions we will
consider three leads.
The connections are made to:
E/C1 – the ground electrode being tested
•
S/P2 – A voltage (potential) measurement stake
•
driven into the earth some distance away from
the electrode. Sometimes called the potential
auxiliary electrode
H/C2 – A current stake driven into the earth a
•
further distance away. Sometimes called the
current auxiliary electrode
Figure 3 shows this schematically and Figure 4
shows the three connections made using a typical
ground tester.
The ground tester injects an alternating current
into the earth between the electrode under test
3 Fluke Corporation Checking ground electrode impedance for commercial, industrial and residental buildings.
(E) and the current stake (C2). The ground tester
measures the voltage drop between the P2 stake
and E. It then uses ohms law to calculate the
resistance between P2 and E.
some distance from the electrode under test. Then,
To perform the test you position the C2 stake at
keeping the C2 stake fixed, you move the P2 stake
along the line between E and C2, measuring the
impedance along the way.
Figure 4: A plot of measured impedances versus position of the
potential stake allows us to see the earth impedance
Measurement Tips
• Bring a good, long tape measure.
• Finding the horizontal part of the curve
will require at least 5, but more likely 7
or 9 measurements.
•
It’s a good idea to take three of your
resistance readings with the P2 stake
at 20 %, 40 % and 60 % of the distance
between E and C2. This will allow you
to use the Tagg Slope Technique.
• When placing the stakes make sure
the current stake, the potential stake
and the electrode under test form a
straight line.
• If you get a very high impedance
measurement or over-range, try pouring some water around the test stakes
to improve their contact to earth. This
isn’t cheating since our intention is
not to measure the resistance of our
stakes, but to measure the resistance
of the electrode.
• Keep the potential and current leads
separated to avoid signal coupling
between the two.
• At a new construction site, you may
want to take multiple sets of measurements. Resistance may drop over time
as the earth settles
Because of the possibility of interaction between an
electrode rings, grids or arrays, and the measurement
stakes you should not take shortcuts – plot the Fallof-Potential graph to be sure you are getting accurate
results.
In testing a bonded array of electrodes the
combined resistance of the array will be less than
the lowest reading you measure for any individual
electrode. If, for example, you have two 8-foot rods
spaced more than 8 feet apart you can be confident
that the combined resistance will be substantially
less for the combined system.
The three-wire measurement will deliver good
results if you use a short C1 lead, or if you don’t
mind having a fraction of an ohm of lead resistance
in your reading. For ground resistance measurements over 10 ohms, the effect of the resistance
of the C1 lead will be small. But for very precise
measurements, especially at low resistances, a
four-wire tester allows you add a fourth lead
to eliminate the contribution of the C1 lead. By
running a separate potential lead (P1) to the electrode under test you can take the drop along the C1
current lead out of the measurement.
Table 1: Approximate Distance to Auxiliary Stakes using
the 62 % Rule (in feet)
Depth of Electrode
under Test (E)
6 50 82
8 62 100
20
30
Distance from E to
Potential Stake (P2)
81 131
100 161
Distance from E to
Current Stake (C2)
Close to the electrode, the potential probe is said
to be within the influence of the electrode. Close
to the current probe the voltage is almost the full
voltage output by the tester. But somewhere in the
middle, something interesting happens.
As we move from the influence of the electrodes
and into the mass of the earth, the test current no
longer causes significant change in potential. If
you plot a series of measurements, moving the
potential stake away from the electrode under test,
and towards the current stake you will notice a
flattening of the curve. An ideal curve is shown
in Figure 3 (see previous page).
The flattest part
of the curve is where we read the earth resis-
Table 2: Approximate Distance to Auxiliary Stakes for
Electrode Arrays (in feet)
Widest Dimension
(Diagonal, diameter
or Straight-line) of
Electrode Array under
Test (E)
65 100 165
80 165 265
100 230 330
165 330 560
230 430
Distance from E to
Potential Stake (P2)
tance. In reality, the curve never goes entirely flat
but reaches a very gentle slope where changes in
resistance are small.
The extent of the influence of the electrode
depends on its depth and it area. Deeper electrodes
require that the current stake be driven farther
away (see Table 1). For large ground rings, grids or
arrays the influence of the electrode may extend for
hundreds of feet. Table 2 gives suggested starting
points for current and potential stake placement.
4 Fluke Corporation Checking ground electrode impedance for commercial, industrial and residental buildings.
Distance from E to
Current Stake (C2)
655
The 62 % Rule
Distance From Electrode Under Test Resistance
C2 P2 P2/C2 R
(feet) (feet) (ohms)
300 30 10% 3.7
300 60 20% 4.4
300 90 30% 5.3
300 120 40% 5.8
300 150 50% 6.5
300 180 60% 6.8
300 210 70% 7.0
300 240 80% 7.7
300 270 90% 8.8
Fall-of-Potential Plot
0.0
2.0
4.0
6.0
8.0
10.0
0 50 100 150 200 250 300
P2 Distance from Electrode Under Test (feet)
R (Ohms)
Current
Spike
Potential
Spike
Electrode
Under test
d
62 % d
E
P2
C2
You may be able to use a shortcut if your test meets
the following criteria:
You are testing a simple electrode (not a large
•
grid or plate)
You can place the current stake 100 feet or more
•
from the electrode under test
The soil is uniform
•
Under these conditions you can place the current
stake 100 feet or more from the electrode under test.
Place the potential stake at 62 % of the distance
between the current stake and the electrode under
test and take a measurement. As a check, take two
more measurements: one with the potential probe
3 feet closer to the electrode under test, and one 3
feet farther away (see Figure 5). If you are on the flat
portion of the fall-of-potential curve then the readings should be roughly the same and you can record
the first reading as your resistance.
If you have resistance readings at the 20 %,
40 % and 60 % points between E and C2, then you
can apply the procedure to the data you’ve already
taken.
Calculate the slope coefficient (μ) using three
resistance measurements from 20 %, 40 % and
60 % of the distance from the electrode under test
to the C2 current stake.
( R
– R
μ =
( R
60 %
40 %
– R
40 %
20 %
)
)
Then go to the table in the back of this application
note and look up the P2/C2 ratio that corresponds
to your μ. This will tell you where to look on your
graph to ascertain the earth resistance. For the
sample data in Figure 6:
( 6.8 – 5.8 )
μ =
( 5.8 – 4.4 )
= 0.71
If we go to the table, for μ = 0.71 the corresponding
P2/C2 percentage is 59.6 %. So the approximate
earth resistance would be measured at
(59.6 % X 300 feet), or at 178 feet. This is very
close to our 60 % point at 180 feet, where we
read 6.8 ohms. So it would be safe to say the earth
resistance for the electrode under test is roughly
7 ohms.
Figure 5: Stake positions for the 62 % rule.
The Tagg Slope Technique
Large electrodes or grounding systems require
5 Fluke Corporation Checking ground electrode impedance for commercial, industrial and residental buildings.
some special consideration. If you’ve plotted
resistance readings for nine different P2 locations
and there is no clear flattening on your graph,
then the Tagg Slope Technique (also called the
slope method) can help establish the earth impedance. Figure 6 shows an example dataset for
which there is no obvious flat section. This curve
is characteristic of a test in which the current and
potential probes never get outside the influence of
the electrode under test. There can be a number
of reasons for a curve like this:
For electrode systems that cover large areas it
•
You may not be able to place the C1 stake at the
•
•
may be difficult to place stakes far enough away
center of the electrode
The area you have to place stakes may be limited
Figure 6: Earth impedance can be found from this curve by using
the Tagg Slope Technique
The Selective Method
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The Selective Method is a variation of the
Fall-of-Potential method, available on high-end
ground testers like the Fluke 1625. Testers with
this capability can measure the ground impedance
of a specific ground electrode without disconnecting it from an array or from a structure’s distribution system. This means you don’t have to wait
for a shutdown to test or risk the safety hazards of
disconnecting the electrode from a live system.
The same rules for current stake and potential
stake placement apply as with Fall-of-Potential. If the conditions are met for the 62 % rule
(see previous page) then it can help reduce the
number of measurements. Otherwise it’s a good
idea to build a complete Fall-of-Potential plot. You
can use the Tagg Slope Technique if your curve
does not flatten out.
Both the Fall-of-Potential method and the
Selective Method use stakes to inject current and
measure voltage drop. The big difference is that
selective testing can accurately measure the test
current in the electrode under test.
The utility neutral, building steel and ground
electrode are all bonded and grounded. When
you inject a current into this system of parallel ground connections the current will divide.
In a traditional Fall-of-Potential test you have
no way of knowing how much current is flow-
ing between any
particular electrode
and the C2 current
stake. Selective
testing uses an
integrated, high
sensitivity clamp-on
current transformer
to measure the
test current in the
electrode under
test. Figure 8 shows
how the current
transformer fits into
Figure 7: Connections for selective ground electrode
measurement
Figure 9: Connecting the Saturn GEO X for a stakeless
measurement
6 Fluke Corporation Checking ground electrode impedance for commercial, industrial and residental buildings.
the test circuit. The
selective ground
tester digitally
filters the current
measurement to
minimize the effects
of stray currents.
Being able to
accurately measure
the current in the
electrode under test
effectively isolates
the electrode and
allows us to test
it without disconnecting it from the
system or from
other electrodes.
Stakeless or Clamp-on Method
The “stakeless” or “clamp-on” method allows
you to measure the impedance of a series loop of
ground electrodes. The test is simple and it may be
performed on an electrode that is connected to a
working electric service.
To make the measurement the tester uses a
special transformer to generate a voltage on the
ground conductor at a unique test frequency. It
uses a second transformer to distinguish the test
frequency and measure the resulting current
through the circuit.
This method is available in some Fall-of-Potential
testers (like the Fluke 1625) or in a single clamp on
unit. Figure 9 shows the connection of the source
and measure clamps of the Fluke 1625.
Figure 10 (see next page) shows the equivalent
test circuit for the stakeless method. When you test
a building ground electrode using this method, you
are actually testing a loop including:
Electrode under test
•
Ground electrode conductor
•
The main bonding jumper
•
The service neutral
•
Utility neutral-to-ground bond
•
Utility ground conductors (between poles)
•
Utility pole grounds
•
Because this method uses the service as part of
the circuit, it may be used only after the service has
been completely wired, that is, it cannot be used
prior to hook-up to the utility. In this method the
clamp checks the continuity of the interconnections
of all of the components above. An abnormally high
reading or an open circuit indication on the instrument points to a poor connection between two or
more of the aforementioned critical components.
Figure 8: Connections for selective Electrode Impedance Mesaurement
This method requires a low-impedance path in
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Electrode
Under test
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6
)
parallel with the electrode under test. The ground
electrode of most facilities is in parallel with numerous utility ground electrodes. These electrodes can
be pole electrodes, pole butt plates or un-insulated
neutral conductors. The impedance of the utility
ground electrodes usually combines into a very
low impedance.
Let’s take an example. Say you have 40 pole
electrodes of roughly 20
Ω each, and these electrodes are connected together by a low-impedance
ground wire from pole to pole. The equivalent
resistance of the 40 electrodes in parallel is:
Req =
1
40 x 1/
20Ω
= 1/2Ω
Since half an ohm is small compared to the resistance we expect for our electrode under test, we can
assume that most of the measured resistance is due
to the earth resistance of the electrode under test.
There are some potential pitfalls for this method:
• If you measure in the wrong place in the system,
you might get a hard-wired loop
resistance,
for example on a ground ring or on a bonded
lightning protection system. If you were intending to read earth resistance, measuring the
conductive loop would give unexpectedly low
resistance readings.
• You may get low readings due to the interaction
of two very close, bonded electrodes, like buried
conduit, water pipes, etc.
The quality of the measurement depends on
•
the availability of parallel paths. If a building
is solely supplied by a generator or transformer
that has only a single electrode, the assumption
of multiple paths won’t work and the measurement will indicate the earth resistance of
both electrodes.
This method will not measure
earth resistance.
A problem with the utility grounding system
•
might interfere with readings.
In general, if you get readings below 1 ohm,
double-check to make sure you are not measuring
a hard-wired conductive loop instead of the
earth resistance.
Two-pole Method
The two-pole method uses an “auxiliary electrode”
such as a water pipe. Figure 11 shows the connections. The tester measures the combined earth
resistance of
the electrode
under test, the
earth resistance
of the auxiliary
electrode, and
the resistance
of the measurement leads.
The assumption is that the
earth resistance
of the auxiliary electrode
is very low,
which would
probably be
true for metal
pipe without plastic
segments or
insulated joints.
The effect of the measurement leads may be
removed by measuring with the leads shorted
together and subtracting this reading from the final
measurement.
Although it’s convenient, be very careful using
the two-pole method:
A water pipe may have PVC components, which
•
could greatly increase its earth resistance. In
this case the two-point method would give an
excessively high reading.
The auxiliary electrode may not be outside the
•
influence of the electrode under test. In this case
Figure 11: Equivalent circuit for two-point
measurement
the reading might be lower than
reality.
Because of the unknowns
involved in this technique, it is
recommended only when the
grounding system and auxiliary
electrode are well known.
Figure 10: Test current paths in the stakeless method
7 Fluke Corporation Checking ground electrode impedance for commercial, industrial and residental buildings.
Summary of Ground Electrode Test Methods
Advantages Drawbacks
Fall-of-Potential • Widely accepted
• When you see the character
istic curve you know you’ve
got a good measurement.
Selective Method • Don’t have to disconnect
electrode
• Widely accepted
• When you see the character
istic curve you know you’ve
got a good measurement.
Stakeless Method • Convenience • Assumes a low-impedance
Two-pole Method • Convenience • Impossible to judge the
• You have to disconnect the
-
ground
• The stakes may not be easy
to drive
• There may not be space
around the ground electrode
to drive the stakes
• The stakes may not be easy
to drive
• There may not be space
-
around the ground electrode
to drive the stakes
parallel path
• Possible to get very low
readings by mistakenly
measuring on a hard-wired
loop
integrity of the “auxiliary
electrode.”
• Can’t be sure you are outside
the area of influence
Table for the Tagg Slope Technique
(for 2 decimal places)
P2/C2
µ
%
0.40 64.3
0.41 64.2
0.42 64.0
0.43 63.9
0.44 63.7
0.45 63.6
0.46 63.5
0.47 63.3
0.48 63.2
0.49 63.0
0.50 62.9
0.51 62.7
0.52 62.6
0.53 62.4
0.54 62.3
0.55 62.1
0.56 62.0
0.57 61.8
0.58 61.7
0.59 61.5
0.60 61.4
0.61 61.2
0.62 61.0
0.63 60.9
0.64 60.7
8 Fluke Corporation Checking ground electrode impedance for commercial, industrial and residental buildings.
P2/C2
µ
0.65 60.6
0.66 60.4
0.67 60.2
0.68 60.1
0.69 59.9
0.70 59.7
0.71 59.6
0.72 59.4
0.73 59.2
0.74 59.1
0.75 58.9
0.76 58.7
0.77 58.5
0.78 58.4
0.79 58.2
0.80 58.0
0.81 57.9
0.82 57.7
0.83 57.5
0.84 57.3
0.85 57.1
0.86 56.9
0.87 56.7
0.88 56.6
0.89 56.4
%
P2/C2
µ
0.90 56.2
0.91 56.0
0.92 55.8
0.93 55.6
0.94 55.4
0.95 55.2
0.96 55.0
0.97 54.8
0.98 54.6
0.99 54.4
1.00 54.2
1.01 53.9
1.02 53.7
1.03 53.5
1.04 53.3
1.05 53.1
1.06 52.8
1.07 52.6
1.08 52.4
1.09 52.2
1.10 51.9
1.11 51.7
1.12 51.4
1.13 51.2
1.14 50.9
%
P2/C2
µ
1.15 50.7
1.16 50.4
1.17 50.2
1.18 49.9
1.19 49.7
1.20 49.4
1.21 49.1
1.22 48.8
1.23 48.6
1.24 48.3
1.25 48.0
1.26 47.7
1.27 47.4
1.28 47.1
1.29 46.8
1.30 46.5
1.31 46.2
1.32 45.8
1.33 45.5
1.34 45.2
1.35 44.8
1.36 44.5
1.37 44.1
1.38 43.8
1.39 43.4
%
P2/C2
µ
1.40 43.1
1.41 42.7
1.42 42.3
1.43 41.8
1.44 41.4
1.45 41.0
1.46 40.6
1.47 40.1
1.48 39.7
1.49 39.3
1.50 38.9
1.51 38.4
1.52 37.9
1.53 37.4
1.54 36.9
1.55 36.4
1.56 35.8
1.57 35.2
1.58 34.7
1.59 34.1
%
Fluke. Keeping your world
up and running
Fluke Corporation
PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
In the U.S.A. (800) 443-5853 or
Fax (425) 446-5116
In Europe/M-East/Africa +31 (0) 40 2675 200 or
Fax +31 (0) 40 2675 222
In Canada (800)-36-FLUKE or
Fax (905) 890-6866
From other countries +1 (425) 446-5500 or
Fax +1 (425) 446-5116
Web access: http://www.fluke.com
©2005-2007 Fluke Corporation. All rights reserved.
Specifications subject to change without notice.
Printed in U.S.A. 3/2007 2550440 A-EN-N Rev C
®
.
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