Seven models from 100 to 800 A with Both Sides Grounded measurement
Measuring contact resistance without removing the breaker’s ground connections requires a micro-ohmmeter with a Both Sides Grounded (BSG) mode, which measures the current diverted through the groundings and subtracts it from the result. The RMO-G series brings it to seven models from 100 to 800 A DC with ripple below 1 %: a 30/300 A current clamp powered by the instrument itself measures the grounding current and the device compensates it, with 0.1 µΩ resolution and ±(0.1 % of reading + 0.1 % of full scale) typical accuracy, in an IP67 case of 8 to 11.5 kg.
RMO-G Series key data
- Models and current: RMO100G to RMO800G, up to 800 A DC with ripple below 1 %; all of them work continuously at 100 A and, at maximum current, from 150 s at 200 A down to 5 s at 800 A.
- Range and resolution: 0.1 µΩ to 999.9 mΩ (499.9 mΩ on the RMO800G), expandable to 6 Ω; 0.1 µΩ resolution, or 0.01 µΩ between 1 and 30 µΩ with the optional high-precision module.
- Accuracy: ±(0.1 % rdg + 0.1 % FS) typical and ±(0.2 % rdg + 0.2 % FS) guaranteed, shared by all seven models; automatic current ramps prevent magnetic transients.
- Both Sides Grounded (BSG): 30/300 A current clamp powered by the instrument that measures the current diverted through the groundings and subtracts it to give the real contact resistance.
- Modes and control: SINGLE, CONTIN, BSG and DTRtest (dead-tank breakers); optional remote control unit and probes with trigger button; the RMO100G tests at 100 A with 20 m cables of 16 mm².
- In the field: IP67 plastic case with the lid closed, 8 to 11.5 kg depending on model; memory for 500 time- and date-stamped measurements, USB or RS232 to the PC software.
Advantages
Both Sides Grounded (BSG)
The BSG mode tests the breaker without removing either of the two ground connections: a current clamp powered by the instrument itself measures what flows through the groundings and the device compensates it in the result.
Testing from a distance
The optional remote control unit starts and stops the measurement away from the instrument, and the probes with trigger button chain series of measurements at the same current without returning to the panel.
Output power with reserves
The high output voltage preserves the measuring range at high currents and tolerates long or thin cables: the RMO100G tests at 100 A with 20 m cables of only 16 mm².
Ramps without transients
The current rises and falls in automatically regulated ramps, so magnetic transients barely affect the reading and the typical accuracy stays at ±(0.1% of reading + 0.1% of full scale).
Applications
- Medium- and high-voltage circuit breakers, live tank and dead tank (DTRtest mode).
- GIS bays and disconnectors in substations with both sides grounded.
- Busbars, cable splices and welded high-current joints.
- Fuses and high-current links in the factory or in the field.
- Switchgear manufacturing, commissioning and maintenance per IEEE C37.09 and IEC 62271-100.
About the product
The measuring range spans from 0.1 µΩ to 999.9 mΩ (up to 499.9 mΩ on the RMO800G) and can be expanded to 6 Ω; the optional high-precision module resolves 1 to 30 µΩ with 0.01 µΩ. The internal memory keeps 500 time- and date-stamped measurements, and the PC software drives the test from a PC over USB or RS232 and produces configurable reports.
Accessories: current cables of several cross-sections and lengths, sense cables with clamps, 30/300 A current clamp powered by the instrument, verification shunt, built-in thermal printer, Bluetooth and transport case.
Technical specifications
| Models | RMO100G to RMO800G (7 models) |
| Test current | Up to 800 A DC; ripple below 1% |
| Measuring range | 0.1 µΩ – 999.9 mΩ; expandable to 6 Ω |
| Typical accuracy | ±(0.1% rdg + 0.1% FS) |
| Resolution | 0.1 µΩ; 0.01 µΩ with optional module |
| Test modes | SINGLE, CONTIN, BSG and DTRtest |
| Protection | IP67 with the lid closed |
| Weight | From 8 to 11.5 kg depending on model |
| Guaranteed accuracy | ±(0.2 % rdg + 0.2 % FS) |
Frequently asked questions
Which micro-ohmmeter can test a circuit breaker with both sides grounded?
One with a BSG mode, which measures the current flowing through the groundings and compensates it in the result. The RMO-G series includes it on all seven models, from 100 to 800 A DC, with a 30/300 A current clamp powered by the instrument itself and ±(0.1 % of reading + 0.1 % of full scale) typical accuracy.
Are there portable micro-ohmmeters up to 800 A for substations?
Yes. The RMO800G, the top model of the RMO-G series, injects up to 800 A DC with ripple below 1 % for 5 s (continuously at 100 A) and measures from 0.1 µΩ to 499.9 mΩ; the series weighs 8 to 11.5 kg depending on the model and comes in an IP67 case.
What does the Both Sides Grounded mode bring?
Safety: the breaker is tested with both ground connections in place. The current clamp measures the share diverted through the groundings and the device subtracts it to give the real contact resistance.
How long can it hold the maximum current?
At 100 A every model works continuously; at each model's maximum current, the duration goes from 150 s at 200 A down to 5 s at 800 A, with duty cycles that prevent overheating.
Does it suit dead-tank circuit breakers?
Yes. The DTRtest mode saturates the breaker's current transformers with an internal algorithm before measuring, so magnetisation does not distort the reading.
What is the difference between the seven models?
Only the maximum current (100 to 800 A), the consumption and the weight: the accuracy, the test modes and the measuring electronics are shared by the whole series.
Can I print results next to the breaker?
Yes. The built-in 58 mm thermal printer is optional, and the 500-measurement memory recalls any result with its time and date.
