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Amblyonix 5004 - Ground Resistance Tester, 4 Pole

Type (3 Pole Testers): 4 Pole
Display (3 Pole Testers): Digital
Accuracy: Resistance Accuracy (percent of range): 0-20Ω, ±3% ±1 digit Voltage Measurement Accuracy (percent of range): 1-19.99V, ±3% ±1 digit
Measuring Voltage: 19.99 V
Soil Resistivity: Yes
Power Supply: Battery, Line Powered

Your Price: $1,195.00

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Ground Testers

Ground Testing Instruments offer a comprehensive solution to ground rod resistance and soil resistivity (4 point) requirements. It is the verification that the electrical system ground is connected to the earth ground and meets safety requirements as defined by the National Electrical Code, (NEC), OSHA, NFPA (National Fire Protection Association), the IEEE and other safety and standards organizations.

The National Electrical Code has established minimum safety values. The National Electrical Code, Section 250-56 states that the “system impedance to ground (ground rod) is less than 25 ohms and that facilities with sensitive electrical equipment should be 5.0 ohms or less.”

Here is a list of several Ground Testing Applications

Soil Resistivity- 4 Point Tester
Ground Resistance Rods- 3 Point Tester
Low Ground Resistance Grids or Mats or Plates- 3 or 4 Point Tester
Ground Resistance for Multiple Grounds without disconnecting system- Clamp-On Tester
Step and Touch Potential- 4 Point Tester
Continuity on Bonding or Grounding -2 or 4 Point Tester
Earth Coupling- 3 Point Tester

A grounding system is designed to provide safety for a variety of conditions that may exist

Lightening strikes to protect personnel or system components
Electrical faults
Static Electricity Problems
Voltage Regulations for Safety

A good grounding system will improve the reliability of equipment and reduce the likelihood of damage due to lightning or fault currents. The primary reason that grounding is tested is the fact that resistance to an earth ground rod or system may vary based on changes in climate and temperature and over time. Such changes can be considerable. Over time, corrosion will degrade ground rods and their connections. It is reasonable to consider an annual maintenance program that checks grounds and bonding.

Features to consider when evaluating your selection for Ground Testers

Types of Ground Testing to be Evaluated
Number of Poles (points) for tests to be completed
Display Required
Graphics Required
Memory Required and Capacity
Enclosure IP Ratings
Wiring Spools and Additional Rods Needed
Wiring Capable of Being Disconnected for Portable Clamp-On
Rechargeable Battery or Field Battery Supply
Test Current
Safety Rating
Resolution

Components of Earth Ground Electrode

Resistance of the electrode itself and connections to it, including the clamp and wire connection
Contact resistance between the electrode and the soil adjacent to it
Resistance of the surrounding earth

What affects the ground resistance measured?

The length and depth of the electrode
The diameter of the electrode
The number of electrodes
The total inherent system design

Ground testing systems to be tested also include Multiple Electrodes, Grounding Grids, Grounding Mats and Grounding Plates.

Traditional types of methods for ground testing include

(a) Three Point Fall of Potential for Ground Rods and Grids
(b) Four Point Soil Resistivity Testing
(c) Touch Potential for Electrical Safety (high ground fault possibility)
(d) Two-Point Tests (continuity tests and bonds)
(e) Clamp-On

(a) Three-Point Fall of Potential

Three Point measurements are used when electrodes or grids can be easily disconnected. Three-point measurement is used to measure resistance to ground of ground rods and grids. The potential difference between rods X and P is measured by a voltmeter, and the current flow between rods X and C is measured by an ammeter. Using Ohm’s Law, R = E/I, we may obtain the ground electrode resistance R. It is not necessary to carry out all the measurements when using a ground tester. The ground tester will measure directly by generating its own current and displaying the resistance of the ground electrode under test (Z).

Earth Coupling. In order to measure Earth coupling, a 3 point system is required. It is primarily used to estimate the influence of two earth resistance systems that are not connected to each other.

(b) Four-Point Soil Resistivity (Wenner Method)

The primary purpose of this test is to locate the areas of lowest soil resistivity which is essential for achieving an economical grounding installation. For most applications, the most accurate method is the 4-Point method. The 4-Point method requires the insertion of four equally spaced electrodes in a test area. A known current from a constant current source is passed between the outermost electrodes and a voltage is then measured across the two innermost electrodes. Most ground resistance instruments will also read the resistance of the rod in test directly in ohms. Soil Resistivity is necessary when determining the design and location of the grounding system especially for new installations to meet acceptable ground resistance requirements.

Soil resistivity is a determining factor when measuring the resistance of a grounding site. This determines the electrode resistance and the depth required for acceptable resistance. The resistivity of the soil varies widely throughout the world and changes seasonally. Soil resistivity is determined largely by its content of electrolytes, consisting of moisture, minerals and dissolved salts. A dry soil has high resistivity if it contains no soluble salts.

(c) Touch Potential (Three Pole) for Electrical Safety (high ground fault possibility)

Touch Potential is the term given to the potential difference a person might experience across their body if they were, for example, standing on the ground outside the perimeter fence of a substation and touching the fence at the time a fault to earth occurred. These tests are recommended when the ground cannot be disconnected, where ground faults are highly likely to occur, or when the “footprint” of grounded equipment (the outline of the part of equipment in contact with earth) is comparable to the size of the ground to be tested. Touch potential is defined as the voltage between an energized object and the feet of a person that may be in contact with that object. In cases close to power distribution sites and fences, the touch potential can be extremely dangerous and hazardous. A four pole tester is used for “touch potential” measurements.

Step potential is the potential difference a person would experience between their feet if they walked over the ground in which a fault current existed. A four pole tester is also used for this test.

(d) Two-Point and Four Point Tests (continuity tests and bonds)

Even though Micro-Ohmmeters with Kelvin probes are suggested to be used for primary accurate bond testing resistance values, a simpler and less accurate, quick indication of resistance value may be performed utilizing a 2 pole (2 lead) method measuring DC resistance with less test current.

A 2 Point Test may also be used to measure the continuity resistance of any wired system. It also measure the integrity of all single or multiple ground system connections.

(e) Portable Clamp-On Method for Ground Testing

Clamp-on ground resistance testing offers the ability to measure the ground resistance without disconnecting the ground rods or the wiring of the system. This type of measurement also offers the advantage of including the bonding to ground and the overall grounding connection resistances. One of the most important considerations for the portable clamp-on system would be a series-parallel resistance path down-stream from the measurement point that is lower in resistance than the point being measured. Please note figures below for typical Clamp-on placement for measurement.