Megger’s popular 4-terminal ground testing instrument family includes four basic models with different kit variants for each that include select accessories for greater testing flexibility.
The top-end models (DET4TC2 and DET4TCR2) include a current measuring function for ART (Attached Rod Technique) testing capabilities. With this added function, on-site grounds can be tested separately without having to remove the utility connection (as explained further in this document). They also provide stakeless testing capability. This method allows the operator to use the instrument like a clamp-on ground tester in applications where that method is viable, while also being able to operate as a fall of potential tester if required.
The basic kit includes the test leads, stakes, batteries and calibration certificate, delivered in a tough polypropylene carry case – everything you need to start testing in one package.
All models are rated to IP54, making them truly outdoor instruments. They are designed to meet stringent safety standards and are rated CAT IV 100 V. The ground testers have been designed to be easy to use – a large selector switch makes selection of 2, 3 or 4 pole tests easy with gloved hands – and the design makes the fitting of shorting links to perform 2-pole tests a thing of the past. A large, clear, easy to read LCD and thumb sized test button also make the instruments particularly well suited to the outdoor conditions of ground testing. In addition to this ease of use feature, the instruments automatically check the connection and conditions of the P spike, C spike, and also the level of ground noise, indicating the status on the display. They also include a voltmeter to enable measurement of ground voltage.
The DET4TD2 and DET4TR2 can measure resistance from 0.01 ohms to 20 kΩ, while the DET4TC2 and DET4TCR2 can measure resistance from 0.01 ohms to 200 kΩ, a key capability for soil resistivity testing. Also, to allow accurate testing in noisy environments, the instruments are capable of rejecting noise up to 40 V peak to peak.
The DET4TD2 and DET4TC2 are powered by eight AA batteries which are widely available and also give excellent testing time – the status of these batteries is given by a bar graph on the LCD display, allowing the operator to decide when to change the batteries before they expire. The DET4TR2 and DET4TCR2 are powered from rechargeableAA cells. The battery charger is built in and the instrument is supplied with an AC/DC adapter. For all instruments, the battery status is displayed using a bar-graph.
The DET4TC2 and DET4TCR2 include additional capabilities. By using the optional ICLAMP the user can augment the traditional fall-of-potential measurement method with ART (Attached Rod Technique), which allows electrode testing without disconnection and also leakage current measurements down to 0.5 mA. A second optional clamp, the VCLAMP, enables true stakeless (clamp-on) measurements to be made in situations where driving stakes is not practical.
The DET4TC2 and DET4TCR2 also feature a backlit display, which extends the operational environment of the instrument to cable cellars and other dark locations. Finally, all units have selectable 25 V or 50 V output for compliance with IEC 61557-5. The 25 V output is required for testing in agricultural environments.
|Model DET4TCR2 shown performing the stakeless ground testing method using only clamps.
Proper grounding provides many varied benefits to both people and facilities. It lessens the chance of injury due to faulty installation, reduces the likelihood of damage from lightning strikes and induced voltages, improves the performance of computer, communication and other sensitive equipment and protects against static electricity from friction. Over time, ground systems can degrade or become ineffective. Corrosion and weather influences exert mechanical strain on ground rods and cause metallic corrosion. Catastrophic events like lightning strikes or large fault currents can cause instant degradation. In addition, soil resistivity can change over time due to environmental conditions and facility expansion can create different ground system needs.
The risks from ground system deterioration include potentially deadly electrical shock situations, plant-wide equipment damage, disruption in the performance of sensitive equipment and heat build-up on a single piece of electrical equipment.
The maintenance of an adequate low resistance ground connection is essential to both the protection and performance of any electrical system. Ground testing should be performed both upon installation, to meet design specification, and periodically thereafter in order to maintain service. All Megger models can also perform bonding tests (using an ac signal), to determine that adequate connection has been made from equipment to the grounding system, and can perform soil resistivity tests. This additional function can be used in prospecting, locating, and designing new grounding electrodes and systems. Furthermore, the addition of built-in current clamp capability enables fall of potential testing of attached grounds (ART) without lifting the utility connection and the addition of voltage clamp technology enables stakeless testing from the same instrument.
Grounding electrodes from simple to complex systems can be tested, including:
FEATURES AND BENEFITS
- Primary and secondary electrical grounding systems
- Utility pole grounds
- Lightning protection systems
- Residential grounds
- Machinery safety grounds
- Computer and communication system grounds
- EMI/RFI system grounds
- Antenna and pedestal grounds
- CATV system grounds
- Stakeless testing capability, which allows the operator to use the instrument like a clamp-on tester in applications where the method is viable
- Attached Rod Technique capability, which allows fall of potential testing without the need to disconnect the ground rod
- Multiple, user selectable test frequencies allows the operator to find the most effective frequency for making the measurement
- 200,000 Ω measurement range provides the ability to measure the resistivity of any type of soil
- User selectable test voltage ensures that the units can be used in agricultural environments
- Microprocessor control for improved error detection
- Clear, unambiguous warnings and error indications ensure the reliability of the reading and reduce test time
- Rugged, weatherproof case to IP54 makes the units truly outdoor instruments
- Backlit LCD allows for testing in dark environments
- Noise rejection to 40 V pk to pk allows accurate testing in noisy environments
- Testing kits and certificates supplied — everything needed to start testing immediately
- Accuracy of 2% of reading enhances reliability of measurements
- Voltmeter function included allows you to measure the ground voltage and enhances operator safety
- CAT IV 100V provides increased operator safety