Ground Testers / Voltage Detectors / Phase Detectors

This page explains in detail how to use Hioki ground resistance testers that can be rinsed in water; phase detectors that implement safe, no-metal-contact operation; and portable voltage detectors.

01. Phase detector principle and method of use

Phase detector principle

Procedure for using a phase detector (how to use the Phase Detector PD3129)

1. Checking operation prior to use
Clip the voltage clips to a single wire (live wire) carrying at least 70 V AC and verify that the line voltage indicator lights up.
•    If the indicator lights up: The instrument is functioning properly.
•    If the indicator does not light up: The instrument may be malfunctioning.

2. Checking a wire to see if it’s live
Use either of the voltage clips to check a wire to see if it’s live.

Voltage clip used     Line voltage indicator
R (red)   R-S indicator only
S (white)   R-S indicator and S-T indicator
T (green)   S-T indicator only

3. Detecting phase
1) Attach the phase detector’s voltage clips to a 3-phase AC circuit’s wires outside the insulation.

2) If all wires are live, the R-S and S-T line voltage indicators will light up.

3) If the phase order indicators flash in the order indicated by the arrow, the the connection phase order is correct (R-S-T). The instrument will beep intermittently.

How to use the Phase Detector PD3129/PD3129-10

Introducing safe, contactless phase detection! This video introduces the Phase Detector PD3129/PD3129-10, which provides visual and aural notification of detection results.

02. Voltage detector principle and method of use

Voltage detector principle

No-metal-contact voltage detectors usually detect voltage by means of electrostatic induction. When the voltage detector is placed in contact with the measurement target (for example, a power outlet), there is capacitance between the measurement target and the voltage detector. Similarly, there is capacitance between the voltage detector and its user, and between the user and the ground. If the measurement target is live, a minuscule AC current will flow via the voltage detector and its user. This minuscule AC current is detected using a high resistance inside the voltage detector and indicated to the user by conversion into light and sound. The current that flows is less than 1 μA and poses no danger to the user.

Voltage detector principle

No-metal-contact voltage detectors usually detect voltage by means of electrostatic induction. When the voltage detector is placed in contact with the measurement target (for example, a power outlet), there is capacitance between the measurement target and the voltage detector. Similarly, there is capacitance between the voltage detector and its user, and between the user and the ground. If the measurement target is live, a minuscule AC current will flow via the voltage detector and its user. This minuscule AC current is detected using a high resistance inside the voltage detector and indicated to the user by conversion into light and sound. The current that flows is less than 1 μA and poses no danger to the user.

Procedure for using a voltage detector (how to use the Voltage Detector 3120)

1. Turn on the instrument.
Turn the switch clockwise. If the green LED fails to light up or if it lights up only weakly, replace the batteries.

2. Checking operation prior to use
Using an outlet or other power source that you know has a voltage, verify that the instrument is operating properly.

•    If the red LED lights up and the instrument beeps: The instrument is functioning properly.
•    If the LED gradually goes out and the instrument beeps faintly: Replace the batteries.
•    If the red LED does not light up and the instrument does not beep: The instrument may be malfunctioning.

3. Detecting voltage
Turn the instrument on, verify that the green LED lights up, and place the detector in contact with the object you wish to check.

•    If the red LED lights up and the instrument beeps: The wire is live.
•    If the green LED remains lit up: The wire is not live or is carrying a voltage of 70 V or less.

*The instrument’s maximum detector-to-ground voltage is 600 V AC. Do not use it to measure voltages in excess of that value.

How to use the Voltage Detector 3480/3481

Introducing safe, contactless voltage detection! This video introduces the compact Voltage Detector 3480/3481.

03. Using a ground resistance tester: Measurement principles and reference resistance values

What is a ground resistance tester?

The resistance between a grounding electrode and the earth is generally known as ground resistance. More precisely, ground resistance is the total of the grounding conductor’s resistance, the contact resistance of the grounding conductor and earth, and the earth’s resistance. Ground resistance differs from ordinary resistors in that it has the following special characteristics:

•    Polarizing action
Because the earth behaves like an electrolyte, it exhibits polarizing action such that a DC current produces electromotive force in the opposite direction, making accurate measurement impossible. Consequently, ground resistance is generally measured using a square wave or sine wave at a frequency of several dozens of hertz to 1 kHz.

•    Special measurement setup
Ground resistance is the resistance between a grounding electrode and the earth. It cannot be measured without inserting the electrode into the ground. Since earth has comparatively low resistivity, a voltage drop occurs near the electrode from which the current used to make the measurement flows. Consequently, in order to accurately measure the resistance value of each grounding electrode (the E electrode, S [P] electrode, and H [C] electrode), you must move about 10 m away.

•    Existence of disturbances
Measurement of ground resistance is subject to disturbances such as ground potential and the effects of the auxiliary grounding electrodes. Ground potential caused by leakage current from devices connected to the grounding electrode is superposed on the signal that the ground resistance tester detects, affecting measured values. In addition, if the auxiliary grounding electrodes have a high ground resistance, the measurement current will decrease, making measurement more susceptible to the effects of noise such as ground potential.

The FT6031 is designed to be resistant to these external effects, allowing accurate measurement even under poor conditions.

Ground resistance tester measurement principles

An AC power supply’s voltage is applied between the H (C) and E electrodes, and the AC current I that flows as a result is measured by an ammeter. In addition, the voltage V that occurs between the S (P) and E electrodes when the current I flows is measured using an AC voltmeter.

Then the ground resistance RX of the E electrode is calculated from the measured current I and voltage V. It is not possible to accurately measure the voltage between the H (C) and E electrodes, or the voltage between the H (C) and S (P) electrodes.

Types of grounding installations and grounding reference resistance values

The Technical Standards of Electric Installation set forth the following grounding installation types and ground resistance values*1:

Grounding installation    Ground resistance value
Class A (formerly Class 1)    10 Ω or less
Class B (formerly Class 2)    Calculated value*2
Class C (formerly Class 3)    10 Ω or less*3
Class D (formerly class 3)    100 Ω or less*3

*1 The values from Japanese standards are listed.
Please note that these values vary by country.

*2 Ohm value equivalent to the result of dividing the ground-fault current in amperes of one wire in the circuit on the high-voltage or special-high-voltage side of the transformer by 150 (or, if the low-voltage circuit’s voltage to ground exceeds 150 V due to the combination of the circuit on the low-voltage side of the transformer with [a] the circuit on the high-voltage side of the transformer or [b] a circuit on the special-high-voltage side with a service voltage of 35,000 V or less, by either [1] 300, if equipped with a device that will automatically shut off the high-voltage circuit or special-high-voltage circuit with a service voltage of 35,000 V or less in more than 1 but less than 2 seconds, or [2] 600, if equipped with a device that will automatically shut off the high-voltage circuit or special-high-voltage circuit with a service voltage of 35,000 V in less than 1 second)

*3 If equipped with a device that will automatically shut off the the low-voltage circuit in question within 0.5 seconds in the event of a ground fault, 500 Ω

04. Using the Earth Tester FT6031: Three-pole method

Performing zero-adjustment

Connect the black measurement cord to the E terminal, the yellow measurement cord to the S (P) terminal, and the red measurement cord to the H (C) terminal and short the tips of the three measurement cords as shown in the figure below.

Then operate the ground resistance tester to perform zero-adjustment.

Connecting the measurement cords

Connect the grounding electrode and the E terminal with the black measurement cord.
Carrying the two reels, move to the measurement location while paying out the measurement cords. Insert an auxiliary grounding electrode into the ground once all of the yellow measurement cord has been paid out and connect the yellow measurement cord to the electrode.
Reposition yourself by walking along the straight line connecting grounding electrode E and the auxiliary grounding electrode S while paying out the red measurement cord from its reel.
Insert another auxiliary grounding electrode into the ground once all of the red measurement cord has paid out and connect the red measurement cord to the electrode.

Measuring the ground resistance

Press the power button to turn on the instrument. Then press the Fn button to display “3 POLE.” The ground potential will be displayed.
Pressing the MEASURE button will cause the instrument to automatically check the ground potential, check the auxiliary ground resistance, and measure the ground resistance.
Measurement will complete in about 8 seconds, and the instrument’s display will light up and show the measured value. Check the measured value.

Measuring ground resistance on concrete

Since concrete is a conductor, it is possible to place the auxiliary grounding electrodes on concrete.
Place the auxiliary grounding electrode on the concrete and pour some water over it, or place a wet cloth on top of the auxiliary grounding electrode.
If this method fails to lower the auxiliary grounding electrode’s ground resistance, spread the optional 9050 Grounding Mesh on the concrete, place the auxiliary grounding electrode on top of the grounding mesh, and then pour water over both. Allow the water to soak into the concrete before measuring the resistance. An object such as a metal plate or a sheet of aluminum foil can be used as a substitute for the grounding mesh. However, the grounding mesh is more effective at lowering the auxiliary grounding electrode’s ground resistance.

Since asphalt is an insulator, it is not generally possible to place auxiliary grounding electrodes on asphalt. However, water-moistened asphalt may permit measurement in some cases.

05. Using the Earth Tester FT6031: Simple measurement and the 2-pole method

Performing zero-adjustment

Connect the black L9787 Test Lead to the E terminal on the instrument and the red L9787 Test Lead to the H (C) terminal and connect (short) the tips of the test leads.

Then operate the ground resistance tester to perform zero-adjustment.

Connecting the measurement cords

The figure to the right provides an example of how to connect the measurement cords when measuring a commercial power supply whose neutral (N) side is grounded.

A Class A grounding installation or buried metal object such as a metal pipe can be used as a low-resistance ground resistor for measurement purposes. Be sure the low-resistance ground resistor is at least 5 m away from the grounding electrode being measured. Accurate measurement will not be possible if the resistor is located too close to the grounding electrode.

Measuring the ground resistance

Using a voltage detector or other suitable instrument, verify that the neutral (N) side of the commercial power supply is not carrying a voltage.

Press the power button to turn on the instrument. Then press the Fn button to display “2 POLE.”

Connect the black L9787 Test Lead to the grounding electrode that is serving as the measurement target, and connect the red L9787 Test Lead to the neutral (N) side of the commercial power supply.

The instrument will display the ground potential.

Pressing the MEASURE button will cause the instrument to automatically perform the sequence of measurements described below. The measured value will be displayed for about 3 seconds, and the HOLD indicator will light up.

The instrument will check whether the ground potential peak value falls within the allowable range. Then it will measure the ground resistance. The instrument will measure the total of the grounding electrode’s ground resistance and the ground resistance of the neutral side of the commercial power supply (Rx + Ro).

06. Example measurements using a ground resistance tester

Measuring the ground resistance of the Class D grounding installation of a residential solar power system

 

Measuring the ground resistance of the Class B grounding installation inside a cubicle (2-pole method)

 

Measuring the ground resistance of the Class B grounding installation in a cubicle (3-pole method)