The AMRU-120 measures earth resistance by the 3- and 4-wire method, with a clamp for multiple earth electrodes and with two clamps when auxiliary electrodes cannot be driven into the ground, as well as soil resistivity by the Wenner method and continuity of equipotential bonding and protective conductors.
Measurement methods
- Earth resistance using auxiliary electrodes, by the 3- and 4-wire method.
- Earth resistance using auxiliary electrodes and a clamp, for multiple earth measurements.
- Earth resistance using two clamps, when auxiliary electrodes cannot be driven into the ground.
- Soil resistivity by the Wenner method.
- Continuity of equipotential bonding and protective conductors, with auto-zero and a 200 mA test current, to IEC 60364-6-61:2000 section 6.12.2.
- Resistance of the auxiliary electrodes RS and RH, and interference voltage with its frequency.
Applications
The meter is intended for checking earth electrodes in electrical, industrial and building installations, where it is useful to measure without disconnecting the earthing system or removing electrodes already in place. The clamp and double-clamp methods verify multiple and interconnected earths without interrupting service, while the soil resistivity measurement supports the design of new earthing installations. The 200 mA test current makes work easier on difficult ground, such as sandy or stony soil.
Power, memory and software
It runs from a rechargeable 4.8 V Ni-MH battery pack (3 Ah as standard, 4.2 Ah optional), giving over 500 measurements per charge and recharged through the supplied Z7 adaptor. It stores up to 990 measurements in 10 banks of 99 cells, each with the real-time clock's time stamp, and transfers them to a computer over the supplied USB cable; an optional OR-1 USB radio interface adds wireless transfer from the meter. Two optional PC applications complete the set: one for creating measurement documentation and one for creating drawings and diagrams of the installations measured.
Technical specifications
| Earth resistance (3- and 4-wire) | 0.00 Ω...19.9 kΩ; to IEC 61557-5, from 0.30 Ω |
| Resistance with clamp (3-wire + clamp) | 0.00...1999 Ω; to IEC 61557-5, from 0.44 Ω |
| Resistance with double clamp | 0.00...149.9 Ω |
| Soil resistivity | 0.00 Ωm...999 kΩm (Wenner method) |
| Protective continuity | 0.00 Ω...19.9 kΩ, current ≥200 mA |
| Measurement category | CAT III 600 V, to EN 61010-1 |
| Protection rating | IP54 |
| Memory | 990 measurements (10 banks of 99 cells) |
| Power supply | 4.8 V Ni-MH battery, 3 Ah (4.2 Ah optional) |
| Warranty | 36 months |
Frequently asked questions
Can it measure earths without disconnecting the system?
Yes. The clamp method and the double-clamp method measure earth resistance without disconnecting the connections or removing auxiliary electrodes.
What test current does it use for continuity?
It uses a 200 mA test current with auto-zero, meeting section 6.12.2 of IEC 60364-6-61:2000.
How are measurements transferred to a computer?
Through the supplied USB cable; the optional OR-1 USB radio interface adds wireless transfer from the meter.
What is the maximum test voltage?
The maximum test voltage is selectable between 25 V and 50 V.
How many measurements does it store?
Up to 990 measurements, organised in 10 banks of 99 cells, each with the date and time from the real-time clock.
