AEMC’s Clamp-on Ground Resistance Testers Models 6416 and 6417 measure grounding electrode
system resistance without the use of auxiliary electrodes.
These instruments enable you to
check the integrity of a grounding electrode system
measure leakage current into the grounding system
determine ground voltage as an indicator of a potential unsafe condition
measure resistance, impedance, inductance, current, and voltage
determine the bonding integrity of the grounding system
and store results for later review and analysis
An important feature of these instruments is loop detection.
This is a condition in which the instrument’s transmitted signal injected at the measurement
point loops through a local conductor, rather than the earth.
This can invalidate grounding system impedance measurements.
For example, consider the lightning arrestor system shown on the screen.
This consists of a series of strike termination devices, also called lightning arrestors,
connected to a grid or grounding ring, typically with grounding electrodes at the corners of
the structure.
When you clamp the instrument around an individual grounding electrode below the grid or ring;
the test current induced by the instrument passes through earth and back to the instrument
by way of the other grounding electrodes.
This produces a valid measurement.
If instead the clamp is placed around a connecting conductor; the induced current loops through
the path provided by the conductors instead of the earth.
In this instance, the measurement will reflect the impedance of the conductor loop, not the
earth.
This latter measurement is valid only for ensuring that the metal elements of the grounding
system are bonded together.
To alert the user of the potential presence of a loop measurement, the Models 6416 and
6417 display a LOOP alarm when the measured impedance falls below a pre-defined threshold.
To demonstrate, we’ll first measure the impedance of a typical utility pole ground
wire, which as you can see is around 20 ohms.
Next, we’ll create an electrical loop by attaching a jumper lead to the grounding cable,
above and below the instrument.
This reduces the impedance to below the alarm threshold.
The display now alternates between the measured value and the word LOOP, alerting you of the
possibility that you may be measuring the impedance through the loop created by the
conductors, rather than through earth.
On the Model 6416, loop detection is always enabled, with a pre-set threshold of 1 ohm.
On the Model 6417, you can change this setting through the DataView Ground Clamp-On Control
Panel.
To do this, turn the instrument ON and check that the Bluetooth enabled indicator appears
on the LCD.
If not, turn the dial to SET-UP and press the HOLD key.
Also ensure that the instrument is paired with your computer.
Then open the Control Panel and connect to the instrument.
Consult the Control Panel Help system if you need guidance for making this connection.
With the instrument connected, select Instrument in the menu bar and click Configure.
The Instrument Configuration dialog box opens.
This is the main interface for configuring the Model 6417 through the Control Panel.
The dialog box includes the Loop Alarm section.
This includes a check box for enabling and disabling the loop alarm feature.
Checking this option activates the Threshold field, allowing you to change the default
setting of 1 ohm.
Allowable values range from 0.1 ohm to 199 ohms.
After you complete this field, click Write to Instrument to send the configuration to
the Model 6417.
This concludes our quick demonstration for using loop detection with the Models 6416
and 6417.
For more information about these instruments, please visit our web site.
And be sure to check our YouTube channel for additional instructional videos about other
topics in electronics, including the many products offered by AEMC.