How to Measure Contact Resistance of Circuit Breaker: Step by Step
Measuring contact resistance is essential to verify circuit breaker health, prevent overheating, and comply with international standards like IEC 62271‑100 and IEEE C37.09. This guide gives you a clear, actionable process using a modern handheld loop resistance tester.
What You Need
-
Micro‑ohmmeter (ductor tester) with minimum 100 A DC output
-
Four‑wire (Kelvin) test leads – eliminates lead resistance error
-
PPE (insulating gloves, safety glasses)
Recommended instrument:
Handheld Loop Resistance Tester – battery‑powered, 7‑inch touch screen, selectable 30/50/80/100 A, 0.01 μΩ resolution, 0.5% accuracy, 1000‑record storage, Bluetooth printer option.
Step‑by‑Step Procedure
| Step |
Action |
| 1. Safety |
Isolate breaker, lockout/tagout, verify zero energy, ground, wear PPE. |
| 2. Visual check |
Inspect contacts for burning, dirt, corrosion – clean if needed. |
| 3. Connect |
Use Kelvin clamps: current leads outside, voltage leads inside (close to contacts). Breaker must be closed. |
| 4. Set test |
On the 7‑inch touch screen: choose current (100 A for HV breakers) and duration (5–10 s typical; 60 s available). |
| 5. Measure |
Press start. Tester injects DC current, displays resistance in μΩ. |
| 6. Repeat |
Test all phases. Tester stores up to 1000 records. |
| 7. Analyse |
Compare with manufacturer limits & phase‑to‑phase deviation (≤50% per NETA). |
Typical Acceptable Values
| Breaker Type |
Normal (μΩ) |
Investigate if > (μΩ) |
| Low voltage (MCCB) |
<200 |
300 |
| Medium voltage |
<100 |
150 |
| High voltage |
<50 |
100 |
NETA rule: If any phase exceeds the lowest phase by >50%, inspect that pole.
Key Standards
-
IEC 62271‑100 – test current up to rated current, four‑wire method
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IEEE C37.09 – minimum 100 A DC test current
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NETA ATS/MTS – 100 A, 50% deviation criterion
-
NEMA AB‑4 – proportional test current for MCCBs (our tester offers 30/50 A as well)
Why Choose Our Handheld Loop Resistance Tester
-
True 100 A output – fully meets IEEE C37.09
-
Four‑wire Kelvin method – built‑in accuracy
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0.01 μΩ resolution, 0.5% ±1 μΩ accuracy
-
60‑second max test time – complies with demanding standards
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Battery powered – >600 tests per charge
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Store 1000 results + Bluetooth printing
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Open‑circuit & overheat protection
Best Practices for Accurate Results
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Always use Kelvin connections (current & voltage separate)
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Perform tests at stable room temperature
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Keep test lead resistance ≤10 mΩ (supplied leads meet this)
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Trend historical data – use the internal memory
Conclusion
Measuring contact resistance is a fast, reliable way to catch contact deterioration early. Follow the step‑by‑step above, use a 100 A four‑wire micro‑ohmmeter, and compare results against standards and phase balance. Our Handheld Loop Resistance Tester delivers the performance, portability, and data management you need for efficient field testing.
Need more? Contact us for a demo or technical datasheet.
About Us
Wuhan Hongzhi Gaoce Electrical Technology Co., Ltd. was founded in 2010 and is located in the China Optics Valley, Wuhan East Lake High-tech Development Zone. The company focuses on the R&D and production of high-voltage power testing products. With a team of high-level researchers and technical application talents, and through technical collaboration with China University of Geosciences and Huazhong University of Science and Technology, we have developed and produced numerous power instruments and electrical testing equipment suitable for power system applications.
Wuhan Hongzhi Gaoce Electrical Technology Co., Ltd.
Professional · Accurate · Reliable
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