General CM660 User manual

RUGGED
AUTO RANGING
TRUE RMS
AC/DC CLAMP METERS
USER’S MANUAL
CM660: 0 TO 600A, MAX
CM700: 0 TO 1000A, MAX
Please read this manual carefully and thoroughly before using this product.

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TABLE OF CONTENTS
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Key Features . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 –4
What’s in the Blister Pack . . . . . . . . . . . . . . . . . . . . 4
Product Overview . . . . . . . . . . . . . . . . . . . . . . . 4 –7
Safety Instructions . . . . . . . . . . . . . . . . . . . . . 7 – 10
Setup Instructions. . . . . . . . . . . . . . . . . . . . . . . . . 10
Install Batteries . . . . . . . . . . . . . . . . . . . . . . . . . 10
Operating Instructions. . . . . . . . . . . . . . . . . . 11 – 24
General Instructions. . . . . . . . . . . . . . . . . . 11 – 14
anging Options . . . . . . . . . . . . . . . . . . . . . . 11
Holding eadings . . . . . . . . . . . . . . . . . . . . . 11
Tracking Max and Min eadings . . . . . . 11 – 12
Making elative Measurements . . . . . . . . . . 12
Disabling Auto Power Off (APO). . . . . . . 12 – 13
Using the Analog Bar Graph. . . . . . . . . . . . . . 13
Turning on the Backlight . . . . . . . . . . . . 13 – 14
Measuring AC or DC Current . . . . . . . . . . . 14 – 16
Measuring AC Inrush Current . . . . . . . . . . . . 15
Measuring Microamp Currents . . . . . . . 15 – 16
Measuring AC or DC Voltage. . . . . . . . . . . . 16 – 19
Using the Non-contact Voltage Detector 16 – 19
Measuring esistance . . . . . . . . . . . . . . . . . . . . 20
Checking for Continuity . . . . . . . . . . . . . . . 20 – 21
Checking the Integrity of a Diode. . . . . . . . . . . . 21
Measuring Capacitance . . . . . . . . . . . . . . . . . . . 22
Measuring Frequency and Duty Cycle . . . . 22 – 23
Measuring Temperature . . . . . . . . . . . . . . . 23 – 24
Specifications . . . . . . . . . . . . . . . . . . . . . . . . 24 – 27
Operating & Maintenance Tips . . . . . . . . . . . . . . . 28
Warranty Information . . . . . . . . . . . . . . . . . . . . . . 29
eturn for epair Policy . . . . . . . . . . . . . . . . . . . . 30

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INTRODUCTION
Thank you for purchasing General Tools &
Instruments’ (General’s) CM660 or CM700 Rugged
Auto Ranging True RMS AC/DC Clamp Meter. Please
read this user’s manual carefully and thoroughly
before using the instrument.
Each meter combines the functions of a voltmeter and
a clamp-type ammeter. The meters are designed for
use in an industrial setting by HVAC/R contractors,
building maintenance technicians, MRO
(maintenance, repair and operations) personnel at
process and power plants, electricians and
electrical/electronic technicians.
The only difference between the CM660 and CM700
involves their current measurement range and
resolution. Where the CM660 has a 0 to 600A
measurement range and a maximum current resolution
of 0.01A, the CM700 has a 0 to 1000A measurement
range and a maximum resolution of 0.1A.
Both clamp meters are easy to use and ruggedly built.
Each meets the ETL CAT III 600V, CAT II 1000V safety
standard.
KEY FEATURES
• 16 functions, 49 ranges
• Measures AC/DC current, AC/DC voltage, resistance,
capacitance, frequency and duty cycle
• Also measures temperature from -58° to 1112°
(-50° to 600°C) using included “K” type stem
thermocouple
• Uses beeper to verify integrity of diodes and check
circuits for continuity
• 0 to 200애A/2000애A AC/DC ranges for measuring
flame rod current with 0.1애A/1애A resolution using
included test leads

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• Built-in Non-Contact Voltage (NCV) detector with four
sensitivity settings and audible and visual alerts
• Large backlit digital LCD with two 6000-count
readouts for simultaneous display of real-time
current or voltage on primary readout and line
frequency on secondary readout
• ast-response analog bar graph
• Bright LED work light
• Manual ranging and MIN/MAX display options
• Data HOLD and REL (zero) buttons
• INRUSH mode for measuring surge current during
motor startup
• 1.65 in. (42mm) jaw opening (largest in its class) for
conductors up to 550 MCM resists side torque
• Rugged housing can survive multiple drops onto
concrete from height of 5 ft. (1.6m)
• 20-minute Auto Power Off (APO) function can be
disabled
• ETL certified CAT III 600V, CAT II 1000V
• 3 year limited warranty
WHAT’S IN THE BLISTER ACK
The meter is supplied in a blister pack with a cavity in
the rear for a soft black nylon carrying pouch. Inside
the pouch are a set of double-insulated test leads
with screw-on alligator clips, a “K” type stem
thermocouple probe and plug adapter, 3 “AAA”
batteries and this user’s manual.
RODUCT OVERVIEW
ig. 1 shows the labels and positions of the controls,
indicators and physical structures of the CM660 and
CM700. ig. 2 shows all possible indications on the
LCD of either unit. amiliarize yourself with the
functions and meanings of these controls, indicators
and connectors before moving on to the Setup
Instructions and Operating Instructions.

5
Fig. 1.
The controls,
indicators and
physical structures
of the CM660
and CM700.
1
. Non-contact voltage (NCV) sensor
2 . NCV visual indicator
3 . LED work light
4 . Rotary function switch
5 . Multi-function buttons:
ZERO/REL —Used to 1) Reset DC current
measurement baseline
to 0A, 2) Enter relative
measurement mode
, in which main readout shows
difference between real-time reading and stored
reading shown on secondary readout, 3)
Disable
meter’s Auto Power Off
function.
AUTO
1
2
3
4
7
8
6
5
9

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FU C/I RUSH —1) Selects among resistance
measurement, capacitance measurement, diode
integrity and continuity check modes with rotary
function switch in position, 2)
Switches
between AC and DC
with rotary function switch in
or position, 3)
Enters surge current
measurement mode
with rotary function in
position, 4)
Enters CV sensitivity set mode if
pressed and held when powering on the meter.
MAX/MI —Pressed once, enters Max/Min mode .
Meter displays maximum value recorded during
current measurement session on secondary
readout.
Pressed twice, switches to display
minimum
value recorded during current
measurement session on secondary readout.
Pressed a third time, exits Max/Min mode.
HOLD—Pressed once , holds measured value(s)
(freezes main and secondary readouts).
Pressed
again
, releases both readouts.
—
Pressed briefly , enters manual ranging
mode in broadest range. Each subsequent button
press switches to next-narrowest full-scale
measurement range. Pressing button in narrowest
range returns to auto ranging mode.
Pressed and
held
for >2 seconds, activates display backlight
(and LED work light if rotary function switch is in
or position).
6 . Test lead jacks
7 . Clamp jaw release
8 . Clamp jaw
9 . Battery compartment (on back)

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Fig. 2. All possible display indications
SAFETY INSTRUCTIONS
 Warning 
To avoid possible electric shock or personal injury,
and to avoid damaging the meter or the equipment
under test:
• Do not use the meter in any way not detailed in this
manual or the meter's safety features may be
compromised.
• Before using the meter, inspect the case.
Do not use the meter if it is damaged. Look for
cracks or missing plastic. Pay particular attention to
the insulation around the connectors.
• 
WAR I G Inspect the test leads for damaged
insulation or exposed metal. Check the test leads
for continuity. Replace damaged test leads before
using the meter.
• Verify the meter’s operation by measuring a known
voltage. Do not use the meter if it operates
abnormally. Protection may be impaired. When in
doubt, have the meter serviced.
• 
WAR I G Do not apply more than the rated
voltage, as marked on the meter, between the
terminals or between any terminal and ground.
AUTO

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•  WAR I G Do not measure voltages above 1000V
in Category III installations.
• 
WAR I G Do not measure voltage when the
function switch points to the resistance (ohms),
current, capacitance or temperature settings. Never
measure current when the switch points to the
resistance (ohms), capacitance or temperature
settings.
• Use caution when working with voltages above
42VACRMS, or 60VDC. These voltages pose a shock
hazard.
• Use the proper terminals, function, and range for all
measurements.
• 
WAR I G Do not operate the meter around
explosive gas, vapor, or dust.
• 
WAR I G When using the probes, keep your
fingers behind the finger guards. Do not touch the
metal probes of the test leads when making a
measurement.
• When making connections, connect the black (–)
test lead before connecting the red (+) test lead;
when disconnecting, disconnect the red (+) test
lead before disconnecting the black (–) test lead.
• Disconnect circuit power and discharge all high-
voltage capacitors before measuring/testing
resistance, continuity, diodes, or capacitance.
• or all DC functions in both auto and manual
ranging mode, to avoid the risk of shock due to
possible improper reading verify the presence of
any AC voltages by first using the AC function. Then
select a DC voltage range equal to or greater than
the AC range.
• Before measuring current, turn off power to the
circuit before connecting the meter.
• Do not operate the meter with the case (or part of
the case) removed.

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• Use only three “AAA” batteries, properly installed in
the battery compartment, to power the meter. Do
not use rechargeable batteries.
• Replace the batteries as soon as the low battery
indicator “ ” appears. Operated with weak
batteries, the meter might produce false readings
that could lead to electric shock and personal injury.
• Remove the test leads from the meter before
opening the meter case or battery compartment.
Electr cal Symbols Used On the
Meter and In Th s Manual
Symbol Description Symbol Description
AC (Alternating use
Current)
DC Double
(Direct Current) Insulated
Caution, risk of Risk of danger.
electric shock. Important
Hazardous information.
voltage. Refer to the
manual.
Battery
(Low battery) Earth ground
when shown
on display
Diode Continuity
Beeper
AC or DC AC/DC

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Symbol Description Symbol Description
Application and or measurements
removal from made on building
hazardous live equipment such
conductors as distribution panels,
permitted feeders and short
branch circuits, and on
lighting systems in
large buildings.
SETU INSTRUCTIONS
INSTALL BATTERIES
The battery compartment of the CM660/700 is
located at the back of the meter.
To open the compartment, use a small Phillips-head
screwdriver to remove the single screw securing the
battery compartment cover. Be careful not to lose the
small screw. Put the screw and the cover to the side.
Install the three supplied “AAA” batteries in the
battery compartment. Use the polarity marks
stenciled inside the compartment as a guide.
Replace the battery compartment cover and secure it
with the Phillips-head screw.
or measurements on
circuits connected
directly to the source of
power for a given build-
ing (for example, on the
cable to the power
transformer ahead of
a building’s circuit
breakers). Very high
levels of energy avail-
able at CAT IV level
make arc flash possible.
Auto Power Off
function CAT IV

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O ERATING INSTRUCTIONS
GENERAL INSTRUCTIONS
The CM660/700 provides several functions that can
be applied to measurements and displays of multiple
parameters.
Ranging Options . By default, the meter automatically
chooses the measurement range that maximizes the
resolution of its current, voltage, resistance,
capacitance, frequency and temperature
measurements. The term
AUTO —in reverse type on
the left side of the LCD—indicates operation in auto
ranging mode.
To switch to manual ranging for any measurement
other than frequency, press the button once. This
will make the term disappear and cause the
meter to enter the broadest full-scale range available
for that parameter (see the Specifications section on
pp. 24 to 27 for a list of the measurement ranges
available for each parameter).
Once the meter is in manual ranging mode, each
subsequent press of the button will narrow the
full-scale range by an order of magnitude (a factor of
10). or example, pressing the button with the
meter operating in the 0 to 600애 full-scale manual
range will narrow the full-scale range to 0 to 60애
(and improve measurement resolution). The next
press of the button will narrow the range to 0 to 6애.
When the narrowest full-scale range has been
reached, the next press of the button will cause the
meter to re-enter Auto Ranging mode.
Holding readings . Pressing the HOLD button “freezes”
the values on both the primary and secondary
readouts and causes a reverse-type “H” ( ) to
appear on the top of the LCD. Pressing the button
again releases the hold and removes the .
Tracking Max and Min Readings . Pressing the
MAX/MI button once switches the secondary

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readout to show the largest value of the parameter
being measured since entering that measurement
mode. The primary display and the analog bar graph
below it will continue to show real-time readings.
Pressing the
MAX/MI button a second time switches
the secondary readout to show the
smallest value of
the parameter being measured since entering that
measurement mode. The primary display and the
analog bar graph below it will continue to show real-
time readings.
Pressing the
MAX/MI button a third time resumes
“normal” display operation, with different values in
the primary and secondary readouts.
When the
MAX/MI button is pressed, the meter will
automatically exit Auto Ranging mode and enter
Manual ranging mode using the full-scale range in
effect at that moment.
Making Relative Measurements . Pressing the
ZERO/REL button during measurement of a current,
voltage, resistance or capacitance freezes the value
being measured at that moment on the secondary
readout. The term
REL will appear on the top line of the
LCD to indicate operation in this special mode. In
REL
mode, the primary readout will show the difference
between ongoing measurements and the frozen value.
REL mode is useful for tracking changes in dynamic
processes or deviations from baseline readings.
When the
REL button is pressed, the meter will
automatically exit Auto Ranging mode and enter
Manual ranging mode using the full-scale range in
effect at that moment.
To exit
REL mode and resume operation in “normal”
display operation, press the
ZERO/REL button again.
Disabling Auto Power Off (APO ). By default, the meter
will automatically power itself off if no front-panel
buttons are pressed within any span of 20 minutes.

13
The icon on the left side of the LCD indicates that
the APO function is enabled.
Once the APO function has activated and powered the
meter off, you cannot reactivate the meter simply by
turning the rotary function switch to a different
position. You must either rotate the switch to the
OFF
position and then to another position, or press a
button—any button.
To disable the
APO function, you must power on the
meter in a special way—by pressing and holding the
ZERO/REL button while turning the rotary function
switch to a position other than
OFF . If the meter is
powered on in this way, the icon will not appear.
If the meter is left unattended, it will remain powered
on until its batteries discharge (typically, several days
later).
Using the Analog Bar Graph
The bar graph at the bottom of the LCD (see below)
provides an analog representation of every
measurement shown in digital form on the primary
readout above it.
The key feature of the bar graph is its fast response
time. It can reflect a change in a measured value
10 times more quickly than the digital readout can.
Accordingly, it is useful for tracking parameters that
change very rapidly (a voltage or current, for
example).
Turning On the Backlight
Pressing and holding the button for at least
3 seconds turns on the LCD’s bright white backlight,
making measurements much easier to read in dark
spaces. If the rotary function switch is in the or
position, pressing and holding the button also
turns on the bright white LED work light at the base of
the clamp jaw ( ig. 1, Callout 3).

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To avoid having the backlight drain the meter’s
batteries, the backlight (and work light, if activated)
automatically extinguishes in 20 seconds.
MEASURING AC OR DC CURRENT
 Warning 
Before making current measurements, make certain
that all test leads are disconnected from the meter
terminals.
(1) Set the rotary function switch to the (AC
current) or (DC current) position to match the type
of current you wish to measure. The corresponding
or symbol will appear on the left side of the
LCD. Before measuring DC current, press the
ZERO/REL button to reset the DC current
measurement baseline to
0A .
(2) Squeezing the clamp jaw release to open the jaw,
place it around the conductor whose current you wish
to measure. Be sure to enclose only one conductor
(see figure below). Enclosing both conductors of a pair
will produce a reading of 0.
otes:
Clamp the jaw around one
conductor only.
Close the jaw completely.
Center the wire in the jaw
for highest accuracy.
When measuring DC currents,
observe the “+” polarity mark
on the right jaw to avoid
negative readings.
(3) Read the measured value(s) from the display.
During measurements of AC current, the primary
readout in the center of the LCD shows the measured
current value, while the secondary readout in the
upper right corner shows the frequency of the current.
AUTO

15
Notes:
A. General’s X3000 lex Clamp Adapter (optional)
makes it possible to enclose a thick or hard-to-
reach conductor, a bundle of conductors, or a
busbar carrying up to 3000A. The accessory uses
induction to convert current readings to millivolt
values that can be displayed by the CM660 or
CM700. or more information or to order, visit
www.generaltools.com and enter “ X3000” in the
SEARCH box.
B. General’s ACL10 Line Splitter (optional) makes it
possible to safely attach the CM660 or CM700 to
a line cord carrying up to 15A AC without
separating its conductors, thereby damaging
the cord. or more information or to order, visit
www.generaltools.com and enter “ACL10” in the
SEARCH box.
Measuring AC Inrush Current
To measure the inrush current
of a motor during
startup, press the
FU C/I RUSH button with the rotary
function switch in the position. The term
I R will
appear on the top line of the LCD and the primary
readout will show the motor’s surge current (to a
maximum of 600A for the CM660 and 1000A for the
CM700). or this application, the current is measured
by the clamp jaw, after it has been placed around one
conductor of the motor’s power supply line.
To return to AC current measurement mode, press the
FU C/I RUSH button again.
Measuring Microamp Currents
The CM660/700 provides two dedicated ranges
(0 to 200애A, and 0 to 2000애A) for measuring minute
amounts of AC or DC current (such as from a furnace
flame rod). or this application, the test leads are
placed in series with the device conducting the
current.

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To measure a microamp current:
1. Turn the rotary function switch to the 애A position.
2. Plug the red and black test leads into the red and
black jacks at the bottom front of the meter.
3. Connect the test leads in series with the device
whose current flow you wish to measure.
4. Read the measured current amplitude on the
primary readout.
MEASURING AC OR DC VOLTAGE
 Warning 
Do not measure voltage higher than 1000V. Doing so
may damage the meter’s internal circuitry. If the
voltage is over 1000V, the beeper will sound
continuously, indicating an over-range measurement.
(1) Set the rotary function switch to the position.
By default, when the switch is set to this position the
meter will measure AC voltage. To measure DC
voltage, press the
FU C/I RUSH button to change the
icon at the lower left of the LCD from to .
(2) Plug the red and black test leads into the red and
black jacks at the bottom front of the meter.
(3) Touch or clip the black test lead to the lower-
potential point of the circuit under test, and the red
test lead to the higher-potential point.
(4) Read the measured voltage on the display. If the
test leads are reversed, a minus sign will appear at
the left of the displayed value.
Using the on-contact Voltage Detector
The NCV function provides a safe (non-contact) way
to check whether a line, cable or AC outlet is “hot”
(energized). At the tip of the clamp jaw ( ig. 1, Callout
1) is an NCV sensor that can detect from a short
distance the electromagnetic field created by AC
voltage. If voltage is detected, the meter produces
audible and visual alarms (a beeping sound, and a

17
flashing white light behind a red lens near the tip
( ig. 1, Callout 2)).
Even unloaded AC circuits generate electromagnetic
fields. Although these fields are extremely weak, their
constantly changing nature means that they generate
some current. A sensitive NCV detector can sense this
current via induction, in much the same way that a
sensitive radio receiver can sense weak radio waves.
NCV detectors cannot detect DC voltages, such as
those present in automotive electrical systems. In
addition, the CM660/700 typically cannot detect
120VAC from a distance of more than 0.25 in.
(6.2mm), and never through a wall or metal conduit.
Unlike other NCV detectors with only one sensitivity
level—and therefore the ability to detect only one
range of voltages (typically 50 to 600VAC)—the
detector in the CM660 and CM700 has four sensitivity
levels. They were chosen to optimize voltage
detection over four practical ranges: 12 to 25VAC,
70 to 125VAC, 150 to 240VAC and 250 to 600VAC.
The ability to detect the presence of 12VAC in
noncontact fashion comes in very handy during
troubleshooting of branch circuits and process plant
and industrial automation systems and equipment
such as gas and water valves, fans, lights, relays,
inverters, solenoids and horns. 12VAC is also
commonly used to power hardwired commercial and
residential building doorbells/buzzers and
thermostats. Separately, the CM660/700’s ability to
detect 480V using its lowest sensitivity range makes
troubleshooting and installing generators and
fluorescent lighting ballasts easier, faster and safer.
User-adjustable sensitivity does more than make the
NCV detector in the CM660/700 more versatile. It also
improves the instrument’s performance. The value of
the detector’s highest sensitivity level (12 to 25VAC) is
obvious: it allows non-contact detection of 12VAC, an

18
ability that most other NCV detectors lack. However,
the detector’s lower sensitivity levels, which cover
common AC power voltages, also have great value,
for the following reason.
Merely detecting the presence of 120VAC near a
bundle of wires does not tell you which wire of the
bundle is the “hot” wire; any of the wires could be
activating the alarms. The NCV detector in the
CM660/700 can help you isolate the hot wire. This
application calls for turning down the sensitivity in
stages after the NCV detector senses voltage. As you
reduce sensitivity, at some stage only the energized
wire will produce a field strong enough to activate the
NCV’s alarms. In this way, the adjustable sensitivity of
the CM660/700’s NCV detector takes the guesswork
out of identifying the “hot” wire of a bundle.
By default, powering on the CM660/700 enables the
NCV function (indicated by the term NCV on the left
side of the LCD) and sets it to a sensitivity of 3. At this
level, the corresponding voltage detection range is 70
to 125VAC—optimum for detecting energized outlets
in the U.S.
To disable the CV function or change its sensitivity ,
you must first power off the meter and then power it
back in special way—by pressing and holding the
FU C/I RUSH button while turning the rotary function
switch to a position other than
OFF .
Powering on the meter in this way produces the
following display on the LCD.

19
To change the NCV sensitivity level, press the
button one or more times. Pressing the button
once from a starting sensitivity of 4 changes the level
to 0, effectively disabling the NCV function. Pressing
the button an additional one, two or three times
changes the sensitivity level to 1, 2 and 3,
respectively.
Once you have determined which level of NCV
sensitivity suits your application, use the button
to set it to that level. After you disable the NCV
function or change its sensitivity level, you must then
save the setting by pressing the
HOLD button. The
meter will remember this setting and resume
operation at that sensitivity level the next time it is
powered on, and even after a battery replacement.
 Warning 
The NCV detector in the CM660/700 is designed to
indicate the presence of AC voltage with an amplitude
between 12VAC and 600VAC. Accordingly, do
not
assume that the absence of a positive indication
means that the circuit under test is de-energized (not
“hot”). Although they can cause shock and/or serious
personal injury, voltages below 12V may not be
detected by the CM660/700. Whenever you have
reason to suspect that a line or outlet is “hot”,
confirm your suspicion by measuring the voltage of
the line or outlet using the test leads and with the
meter’s rotary function switch in the position.
To check whether a line, cable or AC outlet is “hot”
(energized), touch it with the tip of the clamp jaw or
bring the tip within 1/4 inch of it. If the beeper sounds
repeatedly and the LED flashes rapidly, the line or
outlet is energized.

20
MEASURING RESISTANCE
 Warning 
To avoid electrical shock or damage to the meter
when measuring resistance or continuity in a circuit,
make sure power to the circuit is turned off and all
capacitors are discharged.
(1) Turn the rotary function switch to the position.
By default, when the switch is initially set to this
position with the test leads
not plugged in, the
meter will automatically enter the 60MΩ range,
display
O.L (indicating an open circuit) on the
primary readout, and display the term
MΩ above
the right end of the bar graph at the bottom of
the LCD.
(2) Plug the red and black test leads into the red and
black jacks at the bottom front of the meter.
(3) Measure the resistance by touching or clipping the
tips of the leads to the desired test points of the
circuit or to the terminals of a component, as
shown below.
(4) Read the measured resistance on the display. If
the measured resistance value is greater than
60MΩ,
O.L will appear on the primary readout.
The meter will take a few seconds to stabilize
when measuring resistances greater than 1MΩ.
CHECKING FOR CONTINUITY
(1) Turn the rotary function switch to the position.
Press the
FU C/I RUSH button once to select the
continuity check function. If test leads are not
plugged into the meter’s front-panel jacks, the
primary readout will show
.OL , with the icon of a
continuity beeper ( ) above it.
ED TEST LEAD BLACK TEST LEAD