Extech Instruments CT80 Manuale utente

User Guide

AC Circuit Load Tester

For use on EPD, GFCI, and AFCI Circuits

Model CT80

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CT80-EN V1.1 08/12

Introduction

Thank you for selecting the Extech CT80 AC Circuit Load Tester.

This device detects 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. The CT80 can be used reliably on GFCI, EPD, and AFCI 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 device is shipped fully tested and calibrated and, with proper use, will provide years of reliable

service.

Features

True RMS AC measurements

Voltage drop measurements on 12A, 15A, and 20A loads

Voltage measurements: Line, ground-to-neutral, and peak

Measures frequency of the voltage

Measures Hot, Neutral, and Ground conductor impedances

Performs shared Neutral test

Checks 3-wire receptacle configuration

Finds false grounds

Tests GFCI, EPD, and AFCI circuits for proper operation

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CT80-EN V1.1 08/12

Safety

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

Earth Ground

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.

Safety Information

The CT80 conforms to CE and UL-1436 GFCI and AFCI testing.

Exceeding the specified measurement limits of this device may compromise the device’s

safety protection characteristics.

Always test the CT80 on a known line voltage source to confirm proper operation before and

after performing tests on other circuits.

Do not use the CT80 if it appears damaged or if the operation of the unit is inconsistent with

the supplied user guide instructions.

Voltages above 60VDC, 42.4Vpk, and 30VAC are considered shock hazards; always observe

best practice safety guidelines and precautions when working with such voltages.

WARNING

CAUTION

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CT80-EN V1.1 08/12

Description

Meter Description

1. AC power cable connection

2. Test menu

3. Hot-Neutral-Ground coded measurement result

4. Primary reading display

5. Secondary reading display

6. LED test status indicators

7. GFCI test button

8. Down arrow button

9. Right arrow button

10. AFCI test button

(Note: AC Power Cord not pictured)

Display Description

A Amps or Amperes (Current)

V Voltage

Vd Voltage Drop

% Percent Voltage Drop

VL Voltage load

Z Impedance

Hz Hertz (cycles per second)

Ohms (Resistance)

G Ground

N or NEUT Neutral

H Hot

mS Milliseconds

kA, mA kilo-amps and milli-amps

ASCC Available Short Circuit Current

Peak Ground to positive peak measurement

RMS Root Mean Square

GFCI Ground Fault Circuit Interrupter

AFCI Arc Fault Circuit Interrupter

EPD Equipment Protection Device test

OL Overload

m, M, k Unit of measure prefixes: milli, mega, and kilo

‘>’ ‘Greater than’ symbol

Over-temperature alarm (meter operation pauses until cool-down)

AFCI test in progress

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CT80-EN V1.1 08/12

Operation Overview

The CT80 AC Circuit Load Tester can test outlets or circuits under load in a matter of seconds for

proper wiring, reverse polarity, and the presence of a ground. The CT80 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 and AFCI testing utility is performed separately per UL-

1436, disrupting the flow of electricity if a functioning GFCI or AFCI is present.

Notes:

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. The meter will switch off automatically if an over-

temperature condition exists; the meter will automatically switch on when the temperature

cools to an acceptable operational range.

The CT80 is a microprocessor controlled device that prioritizes its tasks; taking a reading

and analyzing the results are its top priorities. This is the reason that the keypad may not

respond immediately to a key-press. 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.

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 with this equipment

Interpreting Measurement Results

Measurement Modes

There are the four (4) measurement modes available. These are:

1. Voltage (V)

2. Voltage drop (Vd)

3. ASCC (Available short circuit current)

4. Impedance (Z)

These measurement modes are shown on the upper left side of the display. Use the ▼button to

scroll through the mode list. Measurement results are shown on the main Wiring Configuration icon

located on the upper right of meter display in conjunction with the two LED status indicators located

above the down arrow button. Interpreting the measurement results is covered in the following

sections.

Measurement Results Coding

The three circles on the wiring configuration icon in conjunction with the two rectangular LED status

indicators are coded to indicate the test result such as for correct wiring, reverse polarity wiring, and

‘no ground’ condition. The wiring configuration icon and the LEDs change appearance (clear, solid,

flashing) to indicate the measurement results. The test results coding and a legend for interpreting

the codes are provided below.

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CT80-EN V1.1 08/12

Illustrated Measurement Result Codes and Legend

The G, N, and H circles (representing Ground, Neutral, and Hot respectively) appear on the CT80s

display and can be ON, OFF, or Flashing as shown in the legend and test result codes below. The

two LED status indicators (located above the down arrow button) can be ON or OFF as shown in the

legend and result codes below.

OFF

FLASHING

ON (LED)

OFF (LED)

Legend:

Note: For open HOT, open NEUTRAL, and H-G polarity reversal conditions, the meter is completely

switched OFF and therefore no display or LED status is available.

Open Hot,

Open Neutral, or

H - G Reversed

(blank display)

H-N Polarity

Reversed

(red display)

H-N Polarity

Reversed and

No Ground

(red display)

Correct

(blue display)

No Ground

(red display)

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CT80-EN V1.1 08/12

The Voltage (V) Measurement Menu

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) Measurement Menu

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 for the 12A and 20A displays.

The Impedance (Z) Measurement 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 these sub-menu items.

Note that testing ground impedance will trip a GFCI circuit.

The ASCC Measurement Menu

The ASCC window indicates the Available Short Circuit Current that the branch current can move

through a breaker in a short circuit situation.

For more specific information on the four measurement modes briefly described above, refer to the

testing examples provided later in this guide.

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 in the ‘Testing Procedures’ section below.

AFCI Button

Depressing the AFCI button displays the AFCI main menu. Two tests can be performed from this

menu: AFCI and NEUT. The AFCI tests Arc Fault Circuit Interrupting devices by creating a 106-141

amp short-duration arc between the hot and neutral conductors per UL1436. The NEUT tests for a

Shared Neutral or falsely grounded neutral conductor, which causes AFCI breakers to nuisance trip

with normal loads. This test applies 300mA between hot and neutral to ensure that the AFCI

breaker does not trip.

Refer to the testing procedures below for more detailed and application specific testing information.

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CT80-EN V1.1 08/12

Testing Procedures

Test 1: Wiring Verification

The wiring configuration is the first test result that is displayed. Refer to the test result codes and

legend presented earlier in the user guide.

For wiring conditions other than normal, the CT80 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 simultaneously display the results of more than one circuit issue

The meter cannot sense ground reversals

Test 2: Voltage Measurements

Warning: Do not take measurements on circuits with voltages higher than 250VAC

(maximum voltage rating).

Line voltage measurements should be within ±10% of the stated line voltage at 50/60Hz. 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 within ±10% of

the stated line voltage)

Utility company problem Contact utility company

High Ground to Neutral voltage

(Readings > 2VAC indicate 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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CT80-EN V1.1 08/12

Test 3: Voltage Drop Measurements

To determine voltage drop, the CT80 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 CT80 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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CT80-EN V1.1 08/12

Test 5: Impedance (Z) Measurements

The impedance measurement capability of the CT80 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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