AEMC instruments Clamp-On 3705 User manual

Clamp-On
Ground Resistance Tester
Model 3705
USER MANUAL
INSTRUMENTS
HOLD
+
–
m A
R1
HOLD
MEM
MR
NOISE
Model 3705
GROUND TESTER
ON
OFF
150V CAT III

Limited Warranty
The Model 3705 is warranted to the owner for a period of two yearsfrom
the date of original purchase against defects in manufacture. This limited
warranty is given by AEMC®Instruments, 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 not performed by AEMC®
Instruments.
For full and detailed warranty coverage, please read the Warranty
Coverage Card, which is attached to the Warranty Registration Card.
Please keep the Warranty Coverage Card with your records.
What AEMC®Instruments will do:
If a malfunction occurs within the warranty period, you may return the
instrument to us for repair or replacement free of charge, provided we have
your REGISTRATION CARD on file. AEMC®Instruments will, at its option,
repair or replace the faulty material.
If a registration card is not on file, we will require a dated proof of purchase,
as well as your REGISTRATION CARD accompanied by the defective
material.
REGISTER ONLINE AT:
www.aemc.com
Warranty Repairs
What you must do to return an Instrument for Warranty Repair:
First, request a Customer Service Authorization Number (CSA#) by phone or
by fax from our Service Department (see address below), then return the
instrument along with the signed CSA Form. Please write the CSA# on the
outside of the shipping container. Return the instrument, postage or
shipment pre-paid to:
Chauvin Arnoux®, Inc. d.b.a. AEMC®Instruments
15 Faraday Drive • Dover, NH 03820 USA
Tel: [phone] (Ext. 360)
(603)
749-6434 (Ext.
360)
Fax: [phone] or [phone]
[email protected]
Caution: To protect yourself against in-transit loss, we recommend you
insure your returned material.
NOTE: All customers must obtain a CSA# before returning any
instrument.

Table of Contents
Warning .....................................................................................................4
International Electrical Symbols ................................................................4
Receiving Your Shipment..........................................................................5
Packaging..................................................................................................5
Accessories ...............................................................................................5
Important Information - Proper Operation .................................................5
Description ................................................................................................5
Product Construction .............................................................................6
Jaw Design ............................................................................................6
Body Design ..........................................................................................6
Electrical Specifications ............................................................................7
Ground Resistance................................................................................7
Mechanical Specifications.........................................................................7
Safety Specifications.................................................................................8
Model 3705 Controls .................................................................................9
Digital Display Features ..........................................................................10
Function Controls ....................................................................................12
On/Off ..................................................................................................12
Auto-Off ...............................................................................................13
Hold .....................................................................................................13
Resistance...........................................................................................14
Function Access Summary .....................................................................15
Principle of Operation..............................................................................15
Field Applications ....................................................................................17
Pole Ground Rods ...............................................................................17
Service Entrance or Meter...................................................................18
Pad Mounted Transformer...................................................................19
Transmission Towers ..........................................................................20
Central Office Locations ......................................................................20
Service Panel ......................................................................................21

Phone Pedestal ...................................................................................22
Above Telephone Space .....................................................................24
General Measurement Notes ..............................................................24
Calibration Check Loop...........................................................................25
Commonly Asked Questions...................................................................26
Maintenance............................................................................................27
Warning ...............................................................................................27
Battery Replacement Procedure .........................................................28
Troubleshooting ......................................................................................28
Repair and Calibration ............................................................................29
Technical and Sales Assistance .............................................................29

Ground Resistance Tester Models 3705
- 4 -
Warning
These safety warnings are provided to 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 ensuring proper
alignment.
• AEMC®Instruments considers the use of rubber gloves to be
an excellent safety practice even if the equipment is properly
operated and correctly grounded.
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.

Ground Resistance Tester Models 3705
- 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, describing any damage. Save
the damaged packing container to substantiate your claim.
Packaging
The Clamp-On Ground Resistance Tester Model 3705 (Cat. #2117.59) is
shipped with a canvas pouch, one 9V battery (not installed), a user
manual with warranty registration and a calibration loop.
Accessories
One multiple calibration loop................................................ Cat. #1223.01
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.
Description
The Ground Resistance Tester Model 3705 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. Simply
clamp the tester around the ground conductor or rod and measure 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 Model 3705 offers battery life information at power-up and Auto-Off
for power management. Additional features are also displayed on the
large LCD to ensure precise measurements.

Ground Resistance Tester Models 3705
- 6 -
Product Construction
The Model 3705 body case is built of Lexan®for rugged use. The probe
heads are encapsulated 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. This product has
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" (32mm) 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 MCM) 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.
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.
Lexan®is a registered trademark of General Electric Corporation.

Ground Resistance Tester Models 3705
- 7 -
Electrical Specifications
Ground Resistance
Measurement Range Range Resolution Accuracy*
0.1 to 1.00Ω0.01Ω± (2% R ± 0.02Ω)
1.0 to 50.0Ω0.1Ω± (1.5% R ± 0.1Ω)
50.0 to 100.0Ω0.5Ω± (2.0% R ± 0.5Ω)
100 to 200Ω1Ω± (3.0% R ± 1Ω)
200 to 400Ω5Ω± (6.0% R ± 5Ω)
400 to 600Ω10Ω± (10% R ± 10Ω)
Autoranging
0.01Ωto 1200Ω
600 to 1200Ω50ΩApprox. 25% ± 50
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.
Resistance Measurement Frequency: 2403Hz
Voltage Generated into the Loop: Approx. 60mVrms
Resistance Overload: OL displayed above 1200Ω
Mechanical Specifications
Dimensions: 9.25 x 3.94 x 2.17" (235 x 100 x 55mm)
Weight: 2.2lbs. (1kg)
Case Material: Lexan®920A (UL94V2) or equivalent
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” (32mm)
Jaw Opening: 1.38” (35mm)
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)

Ground Resistance Tester Models 3705
- 8 -
Storage Temperature: -22° to 158°F (-30° to 70°C)
Altitude: Operational - 2000m; Storage - 12000m
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
Safety Specifications
IEC 1010-2-032 (Class 2), Double Insulation
Working Voltage: 150V, Cat. III - Pollution Degree 2
300V, Cat. II - Pollution Degree 2
Environmental: IP30 (Protection Index) EN 60529 Ed. 92
IK04, EN 50102 Ed. 95
Vibration Test: IEC 68-2-6
Shock Test: IEC 68-2-27
Drop Test (1m): IEC 68-2-32
Max A Overload: 100A continuous, 200A (< 5s) 50/60Hz
OL displayed above 29.99Arms
Electromagnetic Compatibility: Emission: EN 50081-1 Ed. 92
Immunity: EN 50082-1 Ed. 97

Ground Resistance Tester Models 3705
- 9 -
Model 3705 Controls
INSTRUMENTS
HOLD
+
–
m A
R1
HOLD
MEM
MR
NOISE
Model 3705
GROUND TESTER
ON
OFF
150V CAT III
1
2
3
4
5
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.
4. ON/OFF: Power ON or OFF,
activates display self-test at
power-up.
5. Lever: Opens or closes jaws.
Figure 1

Ground Resistance Tester Models 3705
- 10 -
Digital Display Features
+

m A
R.1
HOLD
MEM
MR
NOISE
Displayed when the beeper is active. To turn the beeper On/Off,
push ON & Ωtogether 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 ΩMode. Check
for foreign matter in the jaw mating surface.
In the Ωfunction, 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 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.
Ground resistance measurement mode.
Figure 2
HOLD
NOISE
R
.1

Ground Resistance Tester Models 3705
- 11 -
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.

Ground Resistance Tester Models 3705
- 12 -
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 the remaining battery
life (battery symbol blinks, 0-100% - Fig. 4).
Release the ON/OFF push-button to initialize the instrument.
+
–
m A
R.1 R.1
HOLD
MEM
MR
NOISE
ON
OFF
+
–
m A
HOLD
NOISE
ON
OFF
Model 3705
GROUND TESTER
®
INSTRUMENTS
Model 3705
GROUND TESTER
®
INSTRUMENTS
Figure 3 Figure 4

Ground Resistance Tester Models 3705
- 13 -
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 push-
button. The indicator will appear on the
display to indicate the Auto-Off feature has
been disabled. (Fig. 5).
Hold
The HOLD push-button freezes the last
measured value onto the display. When the
HOLD function is enabled,
HOLD
is displayed
on the LCD.
When the HOLD function is enabled, other
control functions are disabled.
To exit HOLD, press the HOLD push-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 5
Figure 6
Model 3705
GROUND TESTER
®
INSTRUMENTS
ON
OFF
HOLD
ON
OFF
HOLD
Model 3705
GROUND TESTER
®
INSTRUMENTS

Ground Resistance Tester Models 3705
- 14 -
Resistance
The Ωfunction provides resistance measurements from 0.1 to 1200Ωin
seven autoranges.
Range Resolution
0.07 to 1Ω0.01Ω
1.0 to 50.0Ω0.1Ω
50 to 100Ω0.5Ω
100 to 200Ω1Ω
200 to 400Ω5Ω
400 to 600Ω10Ω
600 to 1200Ω50Ω
Upon initial power-on, the Ωfunction is chosen by default.
The Models 3705 will track down to 0.07Ωand
indicate
R
.1
below 0.1Ω(Fig. 7). Accuracy is
not defined below 0.1Ω. Measurements below
0.1Ωtypically (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. 9). This may
indicate high ground resistance but may also be
caused by a disconnected or poorly bonded
ground.
Figure 7
Figure 8
ON
OFF
Model 3705
GROUND TESTER
®
INSTRUMENTS
ON
OFF
R.1
Model 3705
GROUND TESTER
®
INSTRUMENTS

Ground Resistance Tester Models 3705
- 15 -
Function Access Summary
Function Push Button(s)
Used
Function Setting
Saved @ Power Down
On/Off ON/OFF
ΩFunction ON/OFF Default Setting
Display Hold HOLD No
Auto-Off On/Off ON + HOLD No
Principle of Operation
Typically grounded distribution system may be simulated by the basic
circuit shown in Fig. 9 or an equivalent circuit, shown in Fig. 10. 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:
V
I=Rx+ 1
Σ
n
i=1
1
Ri
Rx » 1
Σ
n
i=1
1
Ri
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 25Ωin series with
the equivalent parallel resistance or 0.25Ω. The displayed value would
be 25.2Ω(instrument resolution to 0.1Ω).
V/I = 25Ω+ 0.25ΩRx = 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.
where, usually

Ground Resistance Tester Models 3705
- 16 -
I
V
Rx R1R2Rn-1 Rn
Figure 9
R x R 1
R n
R n-1
Figure 10

Ground Resistance Tester Models 3705
- 17 -
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.
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. 11 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, and pole number. Replace any molding you may
have removed from the conductor.


 


 


Figure 11

Ground Resistance Tester Models 3705
- 18 -
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. 13
shows multiple ground rods and in Fig. 12 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.
 
 


 


 
Water pipe
Service box
Service meter
Pole-mounted
transformer
Building wall
Figure 12
Figure 1
3

Ground Resistance Tester Models 3705
- 19 -
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. 14 and if they are
outside the enclosure, refer to Fig. 15. 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 14
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
R
.1
indicates that you are on a closed loop. In Fig.
19, 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 15