Page 1
Instruction
Manual
ERITECH®Clamp-On
Ground Resistance
Tester Model EST401
EST401
GROUND TESTER
Page 2
Limited Warranty
The Model EST401 is warranted to the owner for a period of one year from the date of
original purchase against defects in manufacture. This limited warranty is given by ERICO
®
,
Inc., not by the distributor from whom it was purchased. This warranty is void if the unit has
been tampered with, abused or if the defect is related to service performed without ERICO,
Inc. authorization.
What ERICO, Inc. will do:
If a malfunction occurs within the one-year period, you may return the instrument to us for
repair, provided we have your proof of purchase. ERICO, Inc. will, at its option, repair or
replace the faulty material.
Warranty Repairs
What you must do to return an Instrument for Warranty Repair:
First, request a Return Material Authorization Number (RMA#) by phone or by fax from
our Service Department (see address below), then return the instrument along with the
RMA Form. Please write the RMA# on the outside of the shipping container. Return the
instrument, postage or shipment pre-paid to:
ERICO, Inc.
34600 Solon Road
Solon, Ohio 44139
Tel: (800) 248-9343 or (440) 542-3832
Fax: (800) 677-8131 or (440) 248-8911
Caution: To protect yourself against in-transit loss, we recommend you insure your
returned material.
NOTE: All customers must obtain an RMA# before returning any instrument.
WARNING
ERICO products shall be installed and used only as indicated in ERICO’s product instruction sheets and training materials. Instruction sheets
are available at www.erico.com and from your ERICO customer service representative. Improper installation, misuse, misapplication or other
failure to completely follow ERICO’s instructions and warnings may cause product malfunction, property damage, serious bodily injury and
death.
WARRANTY
ERICO products are warranted to be free from defects in material and workmanship at the time of shipment. NO OTHER WARRANTY,
WHETHER EXPRESS OR IMPLIED (INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE), SHALL
EXIST IN CONNECTION WITH THE SALE OR USE OF ANY ERICO PRODUCTS. Claims for errors, shortages, defects or nonconformities
ascertainable upon inspection must be made in writing within 5 days after Buyer's receipt of products. All other claims must be made in
writing to ERICO within 6 months from the date of shipment or transport. Products claimed to be nonconforming or defective must, upon
ERICO's prior written approval in accordance with its standard terms and procedures governing returns, promptly be returned to ERICO for
inspection. Claims not made as provided above and within the applicable time period will be barred. ERICO shall in no event be responsible
if the products have not been stored or used in accordance with its specifications and recommended procedures. ERICO will, at its option,
either repair or replace nonconforming or defective products for which it is responsible or return the purchase price to the Buyer. THE
FOREGOING STATES BUYER’S EXCLUSIVE REMEDY FOR ANY BREACH OF ERICO WARRANTY AND FOR ANY CLAIM, WHETHER SOUNDING
IN CONTRACT, TORT OR NEGLIGENCE, FOR LOSS OR INJURY CAUSED BY THE SALE OR USE OF ANY PRODUCT.
LIMITATION OF LIABILITY
ERICO excludes all liability except such liability that is directly attributable to the willful or gross negligence of ERICO's employees. Should
ERICO be held liable its liability shall in no event exceed the total purchase price under the contract. ERICO SHALL IN NO EVENT BE
RESPONSIBLE FOR ANY LOSS OF BUSINESS OR PROFITS, DOWNTIME OR DELAY, LABOR, REPAIR OR MATERIAL COSTS OR ANY SIMILAR
OR DISSIMILAR CONSEQUENTIAL LOSS OR DAMAGE INCURRED BY BUYER.
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Table Of Contents
Limited Warranty.......................................................................................................................
Warranty Repairs .......................................................................................................................
International Electrical Symbols................................................................................................2
Receiving Your Shipment .........................................................................................................3
Packaging................................................................................................................................3
Important Information - Proper Operation ...............................................................................3
Description ..............................................................................................................................4
Product Construction.........................................................................................................4
Jaw Design........................................................................................................................4
Body Design ......................................................................................................................4
Electrical Specifications ............................................................................................................5
Ground Resistance.............................................................................................................5
Ground or Leakage Current...............................................................................................5
Mechanical Specifications ........................................................................................................6
Safety Specifications ................................................................................................................6
EST401 Controls......................................................................................................................7
Digital Display Features............................................................................................................8
Function Controls ....................................................................................................................9
On/Off...............................................................................................................................9
Auto-Off ...........................................................................................................................9
Hold ................................................................................................................................10
Beeper Disable ................................................................................................................10
Resistance .......................................................................................................................11
Current ...........................................................................................................................12
Function Access Summary .....................................................................................................12
Principle of Operation............................................................................................................13
Field Applications ..................................................................................................................14
Pole Ground Rods ...........................................................................................................14
Service Entrance or Meter................................................................................................15
Pad Mounted Transformer ...............................................................................................16
Transmission Towers ........................................................................................................17
Central Office Locations ..................................................................................................17
Service Panel ...................................................................................................................18
Phone Pedestal................................................................................................................19
Above Telephone Space...................................................................................................20
General Measurement Notes ...........................................................................................20
Quick Reference Card............................................................................................................21
Calibration Check Loop .........................................................................................................21
Commonly Asked Questions for Clamp-on Ground Resistance Measurements.......................22
Maintenance .........................................................................................................................23
Battery Replacement Procedure .............................................................................................23
Troubleshooting.....................................................................................................................24
Repair and Calibration...........................................................................................................24
Technical and Sales Assistance ...............................................................................................25
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WARNING
! !
These safety warnings are provided to help ensure the safety of personnel and
proper operation of the instrument.
• The instrument must not be operated beyond its specified operating range.
• Safety is the responsibility of the operator.
• All metal objects or wires connected to the electrical system should be assumed
to be lethal until tested. Grounding systems are no exception.
• Use extreme caution when using the instrument around energized electrical
equipment.
• Never attempt to use the instrument to twist or pry the ground electrode or
ground wire away from the equipment being grounded.
• Open and close the clamp-on jaws slowly to help ensure proper alignment.
• ERICO
®
even if the equipment is properly operated and correctly grounded.
considers the use of rubber gloves to be an excellent safety practice
International Electrical Symbols
This symbol signifies that the instrument is protected by double or reinforced
insulation. Use only specified replacement parts when servicing the instrument.
This symbol signifies CAUTION! and requests that the user refer to the user
!
manual before using the instrument.
Risk of electric shock. The voltage at the parts marked with this symbol may
be dangerous.
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Page 5
Receiving Your Shipment
Upon receiving your shipment, be sure that the contents are consistent with the packing list.
Notify your distributor of any missing items. If the equipment appears to be damaged, file
a claim immediately with the carrier and notify your distributor at once, giving a detailed
description of any damage. Save the damaged packing container to substantiate your claim.
Packaging
The Clamp-On Ground Resistance Tester Model EST401 is shipped with a hard carrying
case, one 9V battery (not installed), an Instruction Manual and a calibration loop. The
manual and calibration check loop are located behind the “egg crate” foam on the inside
of the carrying case cover.
Important Information - Proper Operation
The proper operation and measurement accuracy depends on the proper jaw closing. For
any measurement make sure that the jaw mating surfaces are clean and that no foreign
matter obstructs their closing.
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Description
The Ground Resistance Tester Model EST401 measures ground rod and small grid resistance
through any season, without the use of auxiliary ground rods. Clamp-on ground resistance
testers are used in multi-grounded systems without disconnecting the ground under test.
The EST401 simply clamps around the ground conductor or rod and measures the resistance
to ground. By performing measurements on intact ground systems, the user also verifies the
quality of the grounding connections and bonds. Resistance and continuity of grounding
loops around pads and buildings may also be measured.
The EST401 includes a current measurement function. The probe’s high sensitivity enables
measurement of leakage current flowing to ground or circulating in ground loops down to
1mA and neutral currents to 30Arms. This feature provides additional information which is
becoming vital as distribution ground networks carry higher levels of noise and harmonics
which affect power quality.
Battery life information is given at power-up and Auto-Off for power management.
Additional features are also displayed on the large LCD to ensure precise measurements.
The Buzzer and Auto-Off features may be disabled from the push-buttons at any time.
Product Construction
The EST401 body cases are built of Lexan
ed in a double-walled Lexan shell (or equivalent polycarbonate) for extra strength and are
reinforced at the body interfaces for enhanced field reliability. Overall construction and
mechanical design ratings such as drop test, shock and vibration, weatherproofing against
water projections, meet or exceed IEC (International Electrotechnical Commission)
standards. The products have also been designed to meet IEC 1010.
Jaw Design
The probe head, or jaw, is a key component in the measurement and overall product
performance. Considerable research and development were dedicated to ensuring its
performance, reliability and versatility.
The large jaw has an inner opening diameter of 1.25" (32 mm) permitting use on tight
ground conductors on poles and in manholes. The large opening accommodates not
only ground rods, but larger ground conductors (up to 1000 kcmil) typically found in
telecommunication or railroad applications.
The inner jaw is composed of two independent and individually shielded magnetic cores
permitting the injection of a test signal and accurate return signal measurement without
noise interference or cross talk common to separate probe instruments.
Thorough mechanical design, including small winglets, ensures repetitive jaw alignment
for accuracy and prevents undesirable insertions into the jaw spring assembly.
®
for rugged use. The probe heads are encapsulat-
Body Design
The ergonomic body design permits one-handed operation. The guard provides additional
strength, and prevents the hand from slipping or coming into contact with conductors
under test. The Lexan (or equivalent polycarbonate) body construction provides strength.
The LCD lens cover may be easily replaced if scratched. The sealed push-buttons directly
access all test functions and are easily operated even with gloved hands.
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Electrical Specifications
Ground Resistance
Measurement Range Resolution Accuracy*
Range
0.1 to 1.00Ω 0.01Ω ± (2% R ± 0.02Ω)
1.0 to 50.0Ω 0.1Ω ± (1.5% R ± 0.1Ω)
Autoranging 50.0 to 100.0Ω 0.5Ω ± (2.0% R ± 0.5Ω)
0.01Ω to 1200Ω 100 to 200Ω 1Ω ± (3.0% R ± 1Ω)
200 to 400Ω 5Ω ± (6.0% R ± 5Ω)
400 to 600Ω 10Ω ± (10% R ± 10Ω)
600 to 1200Ω 50Ω Approx. 25% ± 50Ω
Ground or Leakage Current
Measurement Range Resolution Accuracy*
Range
Autoranging
1mA to 30.00A rms
R = Reading
* Reference conditions: 23°C ± 3K, 50% RH ± 10%, battery at 8V ± 0.2V, external
magnetic field < 40A/m, external electrical field < 1V/m, conductor centered, loop
resistance noninductive. Accuracy % of Reading, Frequency: 50/60Hz.
1 to 299mA 1mA ± (2.5% R + 2mA)
0.300A to 2.999A 0.001A ± (2.5% R + 2mA)
3.00A to 29.99A 0.01A ± (2.5% R + 20mA)
Resistance Measurement Frequency: 2403Hz
Voltage Generated into the Loop: Approx. 60mV rms
Resistance Overload: OL displayed above 1200Ω
Current Measurement Frequency: 47 to 800Hz
Influence of Frequency: Add 7.5% to the reference specification
Current Overload: OL displayed above 29.99A rms
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Mechanical Specifications
Dimensions: 9.25 x 3.94 x 2.17" (235 x 100 x 55 mm)
Weight: 2.2 lbs. (1 kg)
Case Material: Lexan
Jaw Cover Material: Lexan with 10% fiberglass charge (UL94V0) or equivalent
LCD Cover Material: Clear Lexan (UL94V1) or equivalent
Color: Gray body, red jaws
Jaw Window Diameter: 1.25” (32 mm)
Jaw Opening: 1.38” (35 mm)
Operating Temperature: 14° to 131°F (-10° to 55°C)
Operating Humidity: 10 to 90% RH @ 14° to 104°F (-10° to 40°C),
75% RH @ 131°F (55°C)
Storage Temperature: -22° to 158°F (-30° to 70°C)
Altitude: Operational - 2000 m; Storage - 12000 m
Power Supply: 9V Alkaline (IEC 6LF22 or NEDA 1604A)
Battery Life: Typical: 8 hours or approx. 1000 measurements of 30 seconds
LCD: 3-3/4 digit, 1.73 x 1.10” (44 x 28 mm)
US Design Patent: No. 362,639
®
920A (UL94V2) or equivalent
Safety Specifications
IEC 1010-2-032 (Class 2), Double Insulation
Working Voltage: 150V, Cat. III - Pollution Degree 2
Environmental: IP30 (Protection Index) EN 60529 Ed. 92
Vibration Test: IEC 68-2-6
Shock Test: IEC 68-2-27
Drop Test (1 m): IEC 68-2-32
Max A Overload: 100A continuous, 200A (< 5s) 50/60Hz
Electromagnetic Compatibility: Emission: EN 50081-1 Ed. 92
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300V, Cat. II - Pollution Degree 2
IK04, EN 50102 Ed. 95
OL displayed above 29.99A rms
Immunity: EN 50082-1 Ed. 97
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EST401 Controls
1
2
7
EST401
GROUND TESTER
1. Head Assembly: Consists of two
individually shielded magnetic cores.
2. Hold: Freezes last measured value
on the display.
3. Display: 3000 count LCD, function
indicators.
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3
4
6
5
Figure 1
4. ON/OFF: Power ON or OFF, activates
display self-test at power-up.
5. Ω: Resistance measurement.
6. A: Current measurement.
7. Lever: Opens or closes jaws.
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Digital Display Features
+
–
m
A
R
.1
HOLD
MEM
MR
NOISE
Figure 2
Displayed when the beeper is active. To turn the beeper On/Off, push ON & Ω
together at power-up. The beeper is active when displayed.
Displayed when the HOLD function is activated. This function locks the present
displayed value. During HOLD: A, Ω, and Alarm functions are deactivated. The
Memory function may still be used.
Indicates that the jaws of the instrument are not properly closed. The Open Jaw
indication is present only in the Ω Mode. Check for foreign matter in the jaw
mating surface.
In the Ω function, this symbol indicates the presence of excessive stray noise in
the ground electrode under test. This symbol will be present if noise signals
reach an amplitude of approx. 5A or 50V. Resistance measurement values are
no longer valid. The beeper is also activated.
Displayed when measured resistance is below 0.1Ω. This may indicate that the
grounding electrode you are clamped onto is continuous with itself (the instrument is measuring a metallic loop and not the ground electrode resistance). In
this situation, electrode resistance measurements may not be valid. The main
display can measure between 0.7 to 0.07Ω, but without any specified accuracy.
Current measurement mode.
,
Ground resistance measurement mode.
Indicates the Auto-Off feature is deactivated and the instrument stays on
permanently (until turned off by the user). With no symbol displayed, after
5 minutes of non-use the instrument will automatically shut itself off. The
Auto-Off feature is turned On/Off by pressing Hold at power-up.
Display flashes this symbol (1/second) during a low battery condition.
Measurements are still possible. When this symbol is displayed continuously,
measurements are no longer possible. Battery replacement is necessary.
Indicates the approximate percentage of useful battery life remaining (0-100%).
This function is displayed only upon initial power-up when the ON push-button
is held down for more than 2 seconds.
The overload symbol will illuminate when the measurement reading is beyond
the limits of the instrument:
Resistance > 1200Ω
Current > 30.00A rms
The beeper is activated in current overload.
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Function Controls
On/Off
The ON/OFF push-button, when pushed, actuates power on or power off with an audible
control tone. Upon initial power-up, the instrument will be in the Ohms function (Ω) and
will go to OL until clamped on. When the ON push-button is pushed and held down, after
three seconds the instrument will beep and provide a self test featuring a full function
display (Fig. 3) followed by status indications for status of remaining battery life
(battery symbol blinks, 0-100%) (Fig. 4).
Release the ON/OFF push-button to initialize the instrument.
Figure 3
Auto-Off
The instrument will shut off automatically after
five minutes of non-use. The instrument will
issue a short beep 15 seconds prior to shutting
down and the LCD flashes once per second.
The Auto-Off may be disabled by turning on the
meter while holding down the HOLD button.
The indicator will appear on the display to
indicate the Auto-Off feature has been disabled.
(Fig. 5).
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Figure 4
Figure 5
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Function Controls
Hold
The HOLD button freezes the last measured value
onto the display. When the HOLD function is
enabled, is displayed on the LCD. (Fig. 6)
When the HOLD function is enabled, other
control functions are disabled (except the
memory function).
To exit HOLD, press the HOLD button and
normal operation is resumed.
Note: When HOLD is pressed during power-up,
the auto-off feature is disabled and is
displayed on the LCD. See Auto-Off.
Figure 6
Beeper Disable
To disable the beeper, press the ON and Ω together
at power-up. The indicator will disappear from
the LCD. (Fig. 7).
This setting is saved indefinitely. To reset the beeper,
press the ON and Ω together at power up.
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Figure 7
Page 13
Function Controls
Resistance
The Ω function provides resistance measurements
from 0.1 to 1200Ω in seven autoranges. (Fig. 8).
Range Resolution
0.07 to 1Ω 0.01Ω
1.0 to 50.0Ω 0.1Ω
50 to 100Ω 0.5Ω
100 to 200Ω 1Ω
200 to 400Ω 5Ω
400 to 600Ω 10Ω
600 to 1200Ω 50Ω
A
EST401
GROUND TESTER
ON
OFF
Upon initial power-on, the Ω function is chosen
by default.
The EST401 will track down to 0.07Ω and
indicate below 0.1Ω (Fig. 9). Accuracy is not
defined below 0.1Ω. Measurements below 0.1Ω
typically (or even 1Ω) indicate the ground tester is
clamped onto a closed loop and that the signal
is not flowing through the ground under test.
If the resistance readings are above 1200Ω, OL will
be displayed on the LCD (Fig. 10). This may indicate
high ground resistance but may also be caused by a
disconnected or poorly bonded ground.
Figure 8
Figure 9
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Figure 10
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Function Controls
Current
Press A to enter the current function. True RMS
current measurements are possible up to 30.00A
(Fig. 11).
Above 30A rms, OL will be displayed and the test
must be discontinued. The beeper is also activated
during OL.
Range Resolution
1 to 299mA 1mA
0.300 to 2.999A 0.001A (1mA)
3.00A to 29.99A 0.01A (10mA)
Function Access Summary
Figure 11
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Function Push Button(s) Function Setting
Used Saved @ Power Down
On/Off ON/OFF
Ω Function Ω Default Setting
A Function A No
Display Hold HOLD No
Auto-Off On/Off ON + HOLD No
Beeper On/Off ON + Ω No
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Principle of Operation
A typically grounded distribution system may be simulated by the basic circuit shown in
Fig. 12 or an equivalent circuit, shown in Fig. 13. If voltage (V) is applied to any measured
grounding electrode Rx through a special transformer, current (I ) flows through the circuit,
thereby establishing the following equation:
∑
n
i=1
1
1
where, usually
Rx
Ri
V
= Rx +
I
Therefore, V/I = Rx is established. If I is detected and measured with V kept constant, the
measured grounding electrode resistance Rx can be obtained. A signal is fed to a special
transformer via a power amplifier from a 2003Hz constant voltage oscillator. The resulting
current is then sensed by a detection CT. An active filter is used to dampen earth current at
commercial frequency and high-frequency noise.
Example: If we clamp around any grounding electrode in a multi-grounded system, the
measured value of the electrode under test will be the resistance of that particular rod in
series with the equivalent parallel resistance value that the rest of the multi-grounded system represents. If we had an electrical system that had 101 grounding electrodes and each
had a resistance value of 25Ω, and we were to clamp around any electrode in the system,
the measured value would be 25Ω in series with the equivalent parallel resistance or 0.25Ω.
The displayed value would be 25.2Ω (instrument resolution to 0.1Ω).
V/I = 25Ω + 0.25Ω
Rx = 25.2Ω
In most field applications, the number of
electrodes that make up a multi-grounded
system would be higher, therefore the
equivalent parallel resistance is negligible
with respect to the rod under test.
»
∑
Figure 12
n
i=1
1
1
Ri
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Figure 13
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Page 16
Field Applications
Pole Ground Rods
Remove any molding covering the ground conductor, and provide sufficient room for the
jaws of the clamp-on. The jaws must be able to close easily around the conductor. The jaws
can be placed around the ground rod itself.
Note: The instrument must be placed so that the jaws close around an electrical path from
the system neutral or ground wire to the ground rod or rods as the circuit provides.
Select the current range “A.” Clamp onto the ground conductor and measure the ground
current. The maximum range is 30.00A Trms. However, if the ground current exceeds 5A
or noise exceeds 50V, ground resistance measurements are not possible. Do not proceed
further with the measurement. Remove the instrument from the circuit noting the
location for maintenance and continue to the next test location.
After noting the ground current, select the ground resistance range (Ω) and measure the
resistance directly. The reading you measure with the clamp-on tester indicates not just
the resistance of the rod, but of the connection to the system neutral and all bonding
connections between the neutral and the rod.
Note that in Fig. 14 there is both a butt plate and a ground rod. In this type of circuit, it is
necessary to place the instrument above the bond so that both grounds are included in the
test. For future reference, note the date, Ohms reading, current reading and pole number.
Replace any molding you may have removed from the conductor.
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Figure 14
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Page 17
Field Applications
Note: A high reading or OL indicates one or more of the following:
A. Poor ground rod
B. Open ground conductor
C. High resistance bonds on the rod or splices on the conductor;
watch for buried split butts, clamps, and hammer-on connections.
Service Entrance or Meter
Follow the same procedure as for Pole Ground Rods. Notice that Fig. 15 shows multiple
ground rods and in Fig. 16 the ground rods have been replaced with a water pipe ground.
You may also have both types acting as a ground. In these cases, it is necessary to make
the measurements between the service neutral and both grounded points.
Figure 16
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Figure 15
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Page 18
Field Applications
Pad Mounted Transformer
Observe all safety requirements - High voltage may be present!
Locate and number all rods (usually only a single rod is present). If the ground rods
are inside the enclosure, refer to Fig. 17 and if they are outside the enclosure, refer
to Fig. 18. If a single rod is found within the enclosure, the measurement should be
taken on the conductor just before the bond on the ground rod. Often, more than
one ground conductor is tied to this clamp, looping back to the enclosure or neutral.
Figure 17
In many cases, the best reading can be obtained by clamping the instrument onto the
ground rod itself, below the point when the ground conductors are attached to the rod,
so that you are measuring the ground circuit. Care must be taken to find the conductor
with only one return path to the neutral.
Generally < 0.7Ω indicates that you are on a closed loop. In Fig. 18, the ground rod
is located outside the enclosure. Clamp at the indicated measuring point to obtain
the correct reading. If more than one rod exists at different corners of the enclosure, it is
necessary to determine how they are connected to properly measure the ground resistance.
Figure 18
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Page 19
Field Applications
Transmission Towers
Observe all safety requirements - Dangerously high voltage may be present!
Locate the ground conductor at the base of the tower. Many different configurations exist.
Care should be taken when searching for the ground conductor. Fig. 19 shows a single leg
mounted on a concrete pad with an external ground conductor. The point at which you
clamp the instrument should be above all splices and connections that allow for multiple
rods, butt wraps, or butt plates.
Note: Current flowing to ground may be high.
Figure 19
Central Office Locations
The main ground conductor from a ground window or a ground plane is usually the
location to clamp the tester. Due to the wiring practices within the central office, there
are many locations at which you can look at the water pipe or counterpoise from within
the building. An effective location is usually at the ground buss in the power room, or
near the backup generator.
By measuring current and resistance at several points and comparing the readings, you
will be able to identify neutral loops, utility grounds and central office grounds. The test
is effective and accurate when the ground window is connected to the utility ground at
only one point.
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Page 20
Field Applications
Service Panel
If we clamp-on the grounding electrode conductor in Fig. 20, the multi-grounded system
required to complete the circuit may be from different sources. These sources may include
the following: Electric Neutral, Phone, CATV, and Water.
The Electric Utility Neutral should be the principle conductor of the low-impedance signal
return path required to test the resistance of this ground electrode with the EST401. This
can be verified by removing other ground connections, noting if any changes appear in the
readings. If by removing one of these signal return paths a much higher reading is noted,
it could mean that the primary signal return path (the Electric Neutral) is defective or open.
Warning: For safety reasons do not remove any ground source without first
!
de-energizing the service panel.
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Figure 20
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Page 21
Field Applications
Phone Pedestal
Provide sufficient room for the EST401 jaws, which must be able to close easily around
the conductor (Fig. 21). The jaws can be placed around the ground rod itself.
Note: If not enough room is available for this task refer to Fig. 22 and continue with
this example. The clamp must be placed so that the jaws are in an electrical path from
the sheath bond(s) or ground bar to the ground rod(s) as the circuit provides.
Select the current range “A.” Clamp onto the ground conductor and measure the ground
current. The maximum current range is 30A. If the ground current exceeds 5A, ground
resistance measurements are not possible. Do not proceed further with the measurement.
Remove the clamp-on tester from the circuit, noting the location for maintenance, and
continue to the next test location.
After noting the ground current, select the ground
resistance range “Ω” and measure the resistance
directly. The reading you measure with the EST401
indicates the resistance of not just the rod, but
also the connection to the sheath ground and all
bonding connections between the sheath bond
and the rod.
A high reading indicates one or more of the
following:
A. Poor ground rod
B. Open ground conductor
C. High resistance bonds on the rod or splices
on the conductor. Also look for bad connections
on the ground bar to the sheath(s).
Note: This same test can be done using the TIP instead
of the sheath ground. However keep in mind that this
is intended to be grounded only back at the central office.
Figure 21
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Figure 22
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Page 22
Field Applications
Above Telephone Space
Select the current range “A.” Clamp onto the ground wire and measure the current
(Fig. 23). The maximum current range is 30A. If the ground current exceeds 5A, resistance
measurements are not possible. Do not proceed further with the measurement. Remove
the clamp-on tester from the circuit, noting the location for attention, and continue to the
next test location.
After noting the current, select the ground
resistance range “Ω” and measure the resistance directly. The reading you measure with
the EST401 indicates the bonding connections
between the Telephone ground and the Power
company ground. One of the following two
scenarios should be observed:
A. If “OL” or a high resistance reading
is displayed this would indicate no
bond has been established or a poor
connection exists between the
Telephone and Power grounds.
B. If and/or a very low reading is
displayed then the bond between
these two grounds has been verified.
Figure 23
General Measurement Notes
A reading of OL is most likely a cable that is not connected to the ground at both ends.
It may be there is no ground rod at all, or that there is no path back to the system neutral.
A reading which is < 0.1Ω generally indicates that the cable where you are clamped is
continuous with itself. You may have located a ground loop, which can usually be confirmed
by comparatively high current readings, also obtained when readings are taken at multiple
locations. A good low resistance ground may also have very high AC current flowing,
depending upon the type of equipment being grounded.
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Page 23
Quick Reference Card
Included with the EST401 you will find a quick reference card like the one shown here.
This card summarizes all the features of the EST401.
Figure 24
Calibration Check Loop
The calibration loop of 25Ω is provided to perform a quick check of the instruments. Check
the clamp-on ground resistance tester by clamping around the loop; the EST401 should read
between 24.2Ω and 25.8Ω.
* Value is for ambient temperature between 68° and 78°F. Value may differ a few counts
under or above this temperature.
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Figure 25
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Commonly Asked Questions for
Clamp-on Ground Resistance Measurements
Q. Can the Clamp-on method be used effectively on high tension towers despite
the distance or spacing between them?
A. Yes. Extended distances will not adversely affect the measurement results. The important
factor is that it be a multiple electrode system.
Q. Does the grounding electrode have to be disconnected and isolated as is
required when using the “Fall-Of-Potential” test with auxiliary electrodes?
A. No. Actually the electrode must be connected to the system to provide the path for test
signal injection as well as to provide the background impedance necessary as the reference.
Additionally, if the tested rod is poorly bonded to the ground connector, a high reading will
be present.
Q. Does this mean I am not able to test an independent electrode?
A. No, however as soon as the connection is made to a multiple electrode system,
usually provided by the connection to the system neutral, you can clamp on and make
a measurement.
Q. Must the instrument be clamped directly on the electrode?
A. No, the instrument will provide valid measurement results when clamped on to the
electrode or the conductor leading to the grounding electrode. The reading through the
conductor will also verify not only the grounding electrode resistance, but connections
of the ground wire to the rest of the system.
Q. Does the system under test have to be energized or de-energized to perform
the test?
A. We are measuring the grounding network. The only requirements are that ground
connections be made to the system under test and that the voltage-to-ground at the
tested point not exceed the instrument rating.
Q. Can the clamp-on method be used for substation grid resistance testing?
A. It depends. It can be used as long as the instrument can be clamped onto a point on
the grounding system at a common point where it ties to the system neutral. Testing a
grid must be treated as if it were a single electrode. Often, clamping on to points within
the grid system will yield a closed loop reading.
Q. How does clamp-on ground testing compare with the standard
“Fall-Of-Potential” test?
A. Empirical testing has validated that when performed correctly, both methods will provide
accurate and repeatable readings for ground electrode resistance.
Q. How large a conductor can the jaw accommodate?
A. The inner diameter of the jaw is 1.25" and can accommodate cables up to 1000 kcmil.
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Maintenance
!
Warning
• To ensure optimum performance, it is important to keep the probe jaw mating surfaces
clean at all times. Failure to do so may result in error in readings. To clean the probe jaws,
use a very fine sand paper (fine 600) to avoid scratching the jaw, then gently clean with
a soft cloth. Do not leave any residue.
• For maintenance use only specified factory replacement parts.
• Avoid electrical shock: do not attempt to perform any servicing unless you are qualified
to do so.
• Avoid electrical shock and/or damage to the instrument: do not allow water or other
foreign substances into the case. Disconnect the unit from all circuits and test cables
before opening the case. Use caution with metallic tools that may short battery packs,
power supplies, etc.
Battery Replacement Procedure
The Clamp-On Ground Resistance Testers are powered by a single 9V battery. The battery
replacement indicator will display continuously when battery replacement is required.
Recommended replacement type is Alkaline (IEC 6LF22, 6LR61 or NEDA 1604A). Ni-Cad
batteries may also be used.
To change the battery, follow this procedure:
1. The instrument must be OFF and disconnected from any conductor.
2. Place the meter face down and remove the two Phillips screws on the back
of the instrument.
3. Remove back cover by pulling it down and away from the instrument.
4. Lift the battery away from the case and disconnect the battery.
5. Connect the new battery and position the leads so that they won’t get pinched
when the cover is replaced.
6. Replace the back cover noting that it slips beneath the hold down lip and fits
securely into position.
7. Install and tighten screws.
Typical battery life is approximately 8 hours of use or about 1000 separate
30-second measurements.
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Troubleshooting
Symptom Indication/Recommended Action
Instrument will not turn ON Low Battery
Continuous audible tone Alarm setpoint tripped
Display is erratic Foreign matter in jaws
Function controls inoperative Hold button on
Light pulsing audible beep Normal operation
Replacement required
Deactivate Alarm or
Change Setpoint Trigger mode
Clean jaw mating surfaces
Turn HOLD off
Battery power management feature
Repair and Calibration
To ensure that your instrument meets factory specifications, we recommend that it be
submitted to our factory Service Center at one-year intervals for recalibration, or as required
by other standards or internal procedures.
For instrument repair and calibration:
You must contact our Service Center for a Return Material Authorization number (RMA#).
This will ensure that when your instrument arrives, it will be tracked and processed
promptly. Please write the RMA# on the outside of the shipping container. If the instrument
is returned for calibration, we need to know if you want a standard calibration, or a
calibration traceable to N.I.S.T. (includes calibration certificate plus recorded calibration
data).
ERICO, Inc.
34600 Solon Road
Solon, Ohio 44139
Tel: (800) 248-9343 or (440) 542-3832
Fax: (800) 677-8131 or (440) 248-8911
(Or contact your authorized distributor)
Costs for repair, standard calibration, and calibration traceable to N.I.S.T. are available.
NOTE: All customers must obtain an RMA# before returning any instrument.
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Technical and Sales Assistance
If you are experiencing any technical problems, or require any assistance with the proper
operation or application of your instrument, please call, mail, fax or e-mail our technical
support hotline:
ERICO, Inc.
34600 Solon Road
Solon, Ohio 44139
Tel: (800) 248-9343 or (440) 542-3832
Fax: (800) 677-8131 or (440) 248-8911
www.erico.com
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Lexan is a registered trademark of General Electric Company
Copyright ©2006 ERICO International Corporation. All rights reserved.
CADDY, CADWELD, CRITEC, ERICO, ERIFLEX, ERITECH, and LENTON are registered trademarks of ERICO International Corporation.
www.erico.com
E1154IS06
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