Extech Instruments CT70 User manual

User's Guide
AC Circuit Load Tester
Model CT70

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Introduction
Congratulations on your purchase of the CT70 AC Circuit Load Tester.
This device can detect circuit and wiring problems such as: Poor ground impedance, false grounds,
missing ground fault protection, low voltage availability under load, and high ground-to-neutral
voltage. In addition, the CT70 tests GFCI and EPD circuits.
Circuit and wiring issues listed above can introduce shock hazards (from grounding issues) and can
comprise performance of machinery and equipment (from poor ground impedance, lack of sufficient
voltage under load and/or high ground-to-neutral voltage). In addition, fire can result from the heat
generated by high resistance points in a circuit.
Proper wiring habits have been shown to greatly increase power quality performance.
This meter is shipped fully tested and calibrated and, with proper use, will provide years of reliable
service.
Features
•True RMS measurements
•Voltage drop measurements on 12A, 15A, and 20A loads
•Voltage measurements: Line, ground-to-neutral, and peak
•Measures frequency of the voltage
•Checks 3-wire receptacle configuration
•Finds false grounds
•Tests GFCI and EPD circuits
Safety
International Safety Symbols
This symbol, adjacent to another symbol or terminal, indicates the user must refer
to the manual for further information.
This symbol, adjacent to a terminal, indicates that, under normal use, hazardous
voltages may be present
Double insulation
This WARNING symbol indicates a potentially hazardous situation, which if not
avoided, could result in death or serious injury.
This CAUTION symbol indicates a potentially hazardous situation, which if not
avoided, may result damage to the product.
WARNING
CAUTION

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Description
Meter Description
1. AC power cable connection
2. Measurement results menu
3. Hot-Neutral-Ground coded measurement result
4. Primary reading display
5. Secondary reading display
6. Down arrow button
7. Right arrow button
8. GFCI test button
Display Description
A Amperes (Current)
V Voltage
Vd Voltage Drop
% Percent Voltage Drop
VL Voltage load
Z Impedance
Hz Hertz (cycles per second)
ΩOhms (Resistance)
mS Milliseconds
ASCC Available Short Circuit Current
Peak Ground to positive peak measurement
RMS Root Mean Square
GFCI Ground Fault
EPD Equipment Protection Device test
NEUT Neutral
OL Overload
m, M, k Unit of measure prefixes: milli, mega, and kilo
2
4
6
1
3
5
7
8

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Operation Overview
The CT70 AC Circuit Load Tester can test outlets or circuits under load for proper wiring, reverse
polarity, and the presence of a ground. The CT70 uses a simple menu-driven display to allow the
user to quickly see line voltage, voltage drop under full load, ground-to-neutral voltage, and line
impedance. The GFCI testing utility is performed separately per UL-1436, disrupting the flow of
electricity if a functioning GFCI is present.
Note: To avoid the buildup of heat during load testing, allow at least 20 seconds to elapse between
tests. In addition to the safety benefits, this will allow the meter to maintain its stated accuracy
during repeated tests.
Warning: To avoid damage to the instrument, do not use this device on the output of a UPS
system, a light dimmer, or a square wave generator.
Warning: Use only the supplied power/test cord (CT70-AC) with this equipment
Interpreting Measurement Results
Important note: The CT70 is a microprocessor controlled device that prioritizes its tasks. Taking a
reading and analyzing the results are its top priorities. This is why, at times, the keypad may not
respond immediately. The internal computer places a higher priority on completing a test than on
recognizing a keystroke. To minimize this effect, press and hold a key until the display menu
changes.
In addition to the main Wiring Configuration icon, shown on the meter display, the measurement
modes are accessed using the four (4) menu items shown on the left side of the display. The menu
items are:
1. Voltage (V)
2. Voltage drop (Vd)
3. ASCC (Available short circuit current)
4. Impedance (Z)
Use the ▼button to scroll the menu list.
The wiring configuration screen shows correct wiring, reverse polarity wiring, and ‘no ground’
conditions. The three circles on the wiring configuration icon indicate the wiring status. The circles
are coded, changing appearance (clear, solid, and flashing) to indicate the measurement results. A
table is provided below for interpreting the circle code.
Blue Display
Red Display
Red Display
Blank Display

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The Voltage menu displays the True RMS line voltage. Use the ►button to scroll the Voltage sub-
menu (line voltage, ground-to-neutral voltage, Peak Voltage (P), and Frequency (Hz)).
The Voltage Drop (Vd) window indicates percent voltage drop (with 15A load) and the Loaded
Voltage (Vl). The voltage drop sub-menu offers a load voltage result for 20A and 12A loads. Use the
►button to scroll the sub-menu.
The Impedance (Z) window indicates the impedance in ohms of the hot conductor. The impedance
sub-menu displays the neutral (N) and ground (G) conductor impedances. Use the ►button to move
through the sub-menu.
Note that testing ground impedance will trip a GFCI circuit.
The ASCC window indicates the Available Short Circuit Current that the branch current can move
through a breaker in a short circuit situation.
GFCI Button
The GFCI (Ground Fault Circuit Interrupt) feature performs two tests:
GFCI: Faults a circuit when 6 to 9mA from hot to ground is detected
EPD (Equipment Protective Device): For breakers equipped with an EPD, the breaker trips for
ground faults greater than 30mA.
To display the GFCI main menu window, press the GFCI button. To toggle the two tests use the ►
button. Once the desired test is selected, press the GFCI button to start the test. These tests are
further detailed below.

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Testing Procedures
Test 1: Wiring Verification
The wiring configuration is the first test result that is displayed. Refer to the table presented earlier in
the user guide for the test result key.
For wiring conditions other than normal, the CT70 is limited in the type of tests it can perform on a
circuit until the circuit’s wiring issues are resolved. For ‘no ground’ conditions, only the line voltage
and voltage drop tests can be made. For reverse polarity conditions, open neutral, or open hot
conditions the meter will not display since power will not be available.
Notes:
•The meter cannot sense two hot wires in a circuit
•The meter cannot display the results of more than one circuit issue at time
•The meter cannot sense ground reversals
Test 2: Voltage Measurements
Warning: Do not take measurements on circuits with voltages higher than 300VAC
(maximum voltage rating).
Line voltage measurements should be 120VAC ±10% at 60Hz. For noise-free sine waves, the peak
voltage should be 1.414 times the rms line voltage reading. Ground to neutral voltage should be less
than 2 VAC in which case the display backlight will appear blue in color, if ground to neutral voltage
is greater than 2 VAC the backlighting appears in red.
Higher ground to neutral voltages indicates excessive current leakage between the neutral and
ground conductors. Excessive ground to neutral voltage may result in inconsistent or intermittent
equipment performance.
Voltage Measurement Troubleshooting Suggestions
Problems Likely Causes Possible Solutions
Overloaded circuit Redistribute loads
Connection within circuit or at
the panel has excessive
resistance
Repair high resistance connection
Out of tolerance Line Voltage
(Line should be 120V±10%)
Utility company problem Contact the power utility company
High Ground to Neutral voltage
(Readings > 2VAC indicated a
problem)
Neutral to Ground current
leakage
Identify leakage, check for multiple
bonding points
Supply voltage out of tolerance Contact power utility companyPeak Voltage out of tolerance (For
120V Line, Peak should measure
between 153 - 183V) High peak loads on circuit Redistribute electronic devices
Frequency out of tolerance
(50/60Hz)
Supply frequency out of
tolerance
Contact power utility company

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Test 3: Voltage Drop Measurements
To determine voltage drop, the CT70 measures line voltage, factors in the load, measures the loaded
voltage, and then calculates the voltage drop. Results for 12A, 15A, and 20A loads are provided. For
nominal efficiency, a voltage drop of 5% is the maximum recommended by the National Electrical
Code (NEC) board. When a voltage drop measurement of less than 5% is made, the meter’s display
backlight turns blue in color. If the voltage drop is higher than 5%, the meter display appears in red.
An efficient branch circuit should have less than 5% voltage drop at the furthest receptacle from the
breaker panel at the termination of the cable run. A steady decrease in the voltage drop should then
be measured for each receptacle tested in sequence towards the breaker panel.
If the voltage drop is higher than 5% and does not noticeably decrease as the testing moves closer
to the first device on the circuit, then the problem lies between the first device and the breaker panel.
Visually check the terminations at the first device, the wiring between the device and the panel, and
the circuit breaker connections.
High resistance points can be identified as hot spots using an infrared (IR) thermometer or by
measuring the voltage across the breaker. If a voltage drop measurement exceeds 5% but noticeably
decreases as the testing moves closer to the panel, then the circuit may have an undersized wire,
too long of a cable run, or excessive current on the circuit. Check the wires to ensure that they are
sized per code and measure the current on the branch circuit. If a voltage drop reading changes
significantly from one receptacle to the next, then the problem could be a high impedance point at or
between two the receptacles. It is usually located at a termination point, such as a bad splice or
loose wire connection, but could also be a faulty receptacle.
Voltage Drop Measurement Troubleshooting Suggestions
Problems Likely Causes Possible Solutions
Overloaded circuit Redistribute loads
Wrong wire gauge size for
length of cable run
Check code and rewire if
necessary
Voltage drop > 5%
High resistance connection in
the circuit or at the panel
Locate bad connection and rewire
or replace
Test 4: ASCC Measurements
The CT70 calculates the ASCC (Available Short Circuit Current) that a branch circuit can deliver
through a breaker in a dead short circuit condition.
The ASCC is calculated by dividing the line voltage by the circuit’s line impedance. See equation
below:
ASCC = Line Voltage / Hot impedance + Neutral impedance
Use the ►button to simulate a situation where all three conductors (hot, neutral, and ground) are
shorted together. Note that this second test will trip a GFCI.

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Test 5: Impedance (Z) Measurements
The impedance measurement capability of the CT70 is used to check Hot and Neutral impedance
when voltage drop measurements are too high (greater than 5%). To determine where the problem
is, measure the impedances and analyze the data as follows:
•If one impedance measurement is exceedingly higher than the other then the problem is
with the conductor that shows the higher impedance.
•If both impedances are high the problem could be an undersized conductor, a faulty load, or
poor connections.
Ground impedance should be less than 1 Ω, preferably in the 0.25 Ωregion to ensure that the
ground conductor can safely return current when necessary.
Surge suppressors require good grounding to adequately protect against transient voltages.
Note: A small amount of current is applied to the ground conductor during impedance measurements
and can trip a GFCI circuit.
High Impedance Troubleshooting Suggestions
Problems Likely Causes Probable Solutions
High hot and/or neutral impedance
(Limit: 0.048Ω/ ft of 14 AWG wire) Excessive loading Redistribute loads
High hot and/or neutral impedance
(Limit: 0.03 Ω/ ft of 12 AWG wire) Undersized wiring Check code and rewire if
necessary
High hot and/or neutral impedance
(Limit: 0.01 Ω/ ft of 10 AWG wire)
High resistance connection in
the circuit or at the panel
Locate bad connection and rewire
or replace
High Ground impedance (Limit: 1Ωfor
personal protection) Undersized wiring Check code and rewire if necessary
High Ground impedance (Limit: 0.25Ω
for equipment protection
High resistance connection in
the circuit or at the panel
Locate bad connection and rewire
or replace

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Test 6: GFCI (Ground Fault Circuit Interrupter) Testing
A ‘GFCI’ can protect personnel from shock hazards. The CT70 tests GFCI circuits by forming a Hot-
Neutral imbalance, leaking small amounts of current (6 to 9 mA) from Hot to Ground through a fixed
resistance.
A good GFCI circuit will sense this imbalance and switch off the power. The CT70 displays the
current value in mA. To test a GFCI circuit:
1. Plug the meter into the receptacle under test.
2. Press the CT70 GFCI button to enter the GFCI test mode menu.
3. GFCI is the default test and the letters ‘GFCI’ should appear on the lower side of the meter’s
display. If not, press the ►button once to switch to ‘GFCI’.
4. Press the GFCI button again to start the test. The current that is leaked to ground will
display. The rotating display affect lets the user know that the test is in progress.
5. The GFCI circuit should typically trip within 200ms (the meter’s display will switch off
because the power has been removed by the GFCI circuit).
6. When the GFCI circuit is reset, the CT70 will display the elapsed time from start of test to
power down.
7. Press any button to return the meter to normal operation mode.
8. If the GFCI circuit fails to respond in 6.5 seconds, the CT70 stops the test automatically and
‘OL’ will display on the meter.
Notes:
1. To test a GFCI circuit on a two wire system, a three-to-two wire adaptor must be used with the
adaptor manually connected to ground (cold water pipe, for example).
2. Appliances connected to the circuit under test should be disconnected to avoid measurement
errors.
Test 7: EPD (Equipment Protective Device) GFCI Testing
An EPD device can protect equipment as well as personnel. The CT70 tests EPD circuits by forming
a Hot-Neutral imbalance, leaking current from Hot to Ground through a fixed resistance. A larger
amount of current (30mA) is used than would normally be used to test a standard GFCI (6 to 9mA). A
good EDP/GFCI circuit will sense this imbalance and switch off the power. The CT70 displays the
current value in mA.
To test an EPD/GFCI circuit:
1. Plug the meter into the receptacle under test.
2. Press the CT70 GFCI button to enter the GFCI test mode menu.
3. GFCI is the default test and the letters ‘GFCI’ will appear on the lower left side of the meter’s
display. Press the ►button once to switch to ‘EPD’.
4. Now follow steps 4 through 8 in Test 6 (GFCI) above.

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Specifications
General Specifications
Display 128 x 64 LED with backlighting
Voltage display update rate 2.5 seconds max.
Over range indication ‘OL’ display
Equipment Power Rating 100 to 250 VAC 3.9 VA, 45 to 65Hz, 18.0mA
Operating Temperature 32°F to 122°F (0°C to 50°C)
Storage Temperature 32°F to 122°F (0°C to 50°C)
Operating Humidity Max 80%
Storage Humidity Max 80%
Case construction ABS UL 94V/0/5VA rated
Altitude 6561.7 ft. (2000m)
Dimensions 8 x 2.8 x 2” (203 x 71 x 51 mm)
Weight 11.2 oz. (317.5g)
Safety approvals CE, ETL
General safety For indoor use and in accordance with the requirements for
double insulation to IEC1010-1 (2001): EN61010-1 (2001)
Overvoltage Category II 300V Pollution Degree 2.
Measurement Specifications
Range and Resolution Accuracy
Line Voltage 100.0 to 250.0 VAC ± (1.0% + 0.2V)
Peak Line Voltage 121.0 to 350.0 VAC ± (1.0% + 0.2V)
Frequency 45.0 to 65.0 Hz ± (1.0% + 0.2Hz)
Voltage drop (%) 0.1 to 99.9% ± (2.5% + 0.2%)
Voltage (under load) 10.0 to 250.0 VAC ± (2.5% + 0.2V)
Neutral to Ground Voltage 0.0 to 10.0 VAC ± (2.5% + 0.2V)
0.00 to 3.00 Ω(Hot) ± (2.5% + 0.02Ω)
Impedance
>3 Ω(Neutral, Ground) Unspecified
GFCI Trip Current 6.0 to 9.0mA ± (1.0% + 0.2mA)
EPD Trip Current 30.0 to 37.0mA ± (1.0% + 0.2mA)

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Support lines: U.S. 877-439-8324, Intl. 603-324-7800
Technical support: Option 3; E-mail: [e-mail]
Repair & Returns: Option 4; E-mail: [email protected]
Product specifications subject to change without notice
Visit our website: www.extech.com
Extech Instruments Corporation, 9 Townsend West, Nashua, NH 03063
ISO 9001 Certified since 1995
Maintenance
WARNING: To avoid electrical shock, remove all inputs before opening the case.
Cleaning and Storage
Periodically wipe the case with a damp cloth and mild detergent; do not use abrasives or solvents to
clean the instrument.
Pack the meter away safely when not in use. Do not allow the meter to remain connected to live
circuitry when not in use.
Warranty
EXTECH INSTRUMENTS CORPORATION (a FLIR company) warrants this instrument to be free of defects in parts and
workmanship for one year from date of shipment (a six month limited warranty applies to sensors and cables). If it should
become necessary to return the instrument for service during or beyond the warranty period, contact the Customer
Service Department for authorization. Visit our website www.extech.com for contact information. A Return Authorization
(RA) number must be issued before any product is returned to Extech. The sender is responsible for shipping charges,
freight, insurance and proper packaging to prevent damage in transit. This warranty does not apply to defects resulting
from action of the user such as misuse, improper wiring, operation outside of specification, improper maintenance or
repair, or unauthorized modification. Extech specifically disclaims any implied warranties or merchantability or fitness for a
specific purpose and will not be liable for any direct, indirect, incidental or consequential damages. Extech's total liability is
limited to repair or replacement of the product. The warranty set forth above is inclusive and no other warranty, whether
written or oral, is expressed or implied.
Calibration and Repair Services
Extech offers repair and calibration services for the products we sell. Extech also provides NIST certification for most
products. Call the Customer Service Department for information on calibration services available for this product. Extech
recommends that annual calibrations be performed to verify meter performance and accuracy.