Extech Instruments CT70 Manual de usuario

User Manual

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 for 120 V circuits

Voltage drop measurements on 5A, 8A, and 10A loads for 230 V circuits

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)

Ohms (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

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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.

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.

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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

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, or 230V +/- 10% at 50Hz. 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

Out of tolerance Line Voltage

(Line should be within ±10% of

the stated line voltage)

Overloaded circuit Redistribute loads

Connection within circuit or at

the panel has excessive

resistance

Repair high resistance

connection

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

Peak Voltage out of tolerance

(For 120V Line, Peak should

measure between 153 - 183V)

(for 230V Line, peak should

measure between 292 357)

Supply voltage out of tolerance Contact power utility company

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 are provided for 120V circuits, with 12A, 15A, and 20A loads and 230V circuits with 5A, 8A,

10A loads.

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 ma

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

Voltage drop > 5% Overloaded circuit Redistribute loads

Wrong wire gauge size for

length of cable run

Check code and rewire if

necessary

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 . 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 , preferably in the 0.25 region 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: 0.048 / ft of 14 AWG wire) Excessive loading Redistribute loads

High hot and/or neutral impedance

(Limit: 0.03 / ft of 12 AWG wire) Undersized wiring Check code and rewire if

necessary

High hot and/or neutral impedance

(Limit: 0.01 / 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: 1

for personal protection) Undersized wiring Check code and rewire if

necessary

High Ground impedance (Limit:

0.25 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

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. hould appear on the lower side of the

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

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

e 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 tes appear on the lower left side of the

ress the

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

Equipment Power Rating 100 to 250 VAC 3.9 VA, 45 to 65Hz, 18.0mA

Operating Temperature 0 C to 50 C (32 F to 122 F)

Storage Temperature 0 C to 50 C (32 F to 122 F)

Operating Humidity Max 80%

Storage Humidity Max 80%

Case construction ABS UL 94V/0/5VA rated

Altitude 2000m (6561.7 ft)

Dimensions 203 x 71 x 51 mm ( )

Weight 317.5g (11.2 oz.)

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 (Single phase) 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)

Impedance

>3 (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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