Causes and Troubleshooting of Switch Circuit Resistance Tester Failures

The Loop Resistance Tester, also known as the RX Transformer Loop Resistance Tester, is an essential tool used in electrical testing, especially for measuring the resistance of conductive loops in various switchgear. According to the updated "Transmission and Preventive Test Regulations for Electrical Equipment," the minimum current required for measuring the conductive loop resistance of switches must be at least 100A. In response to this requirement, our factory has developed a new generation of intelligent loop resistance testers that are both advanced and user-friendly. These devices are ideal for testing the contact resistance of main contacts in high and low voltage switches, as well as the DC resistance of power cables. Here are some common issues users may encounter with the Loop Resistance Tester and their corresponding solutions: 1. **Issue**: The tester is connected to a 220V AC power supply, but the fan does not run, and the “Test Switch” is pressed, yet the ammeter and micro-ohmmeter do not display anything. **Cause**: The 220V AC power is not properly connected, or the fuse is missing or blown. **Solution**: Check the power connection and ensure the fuse is correctly installed. If the 100A instrument’s fuse is blown, replace it with a 6A fuse. Avoid connecting DC or 380V AC power by mistake. 2. **Issue**: After pressing the “Test Switch,” the ammeter shows no current, and the highest digit on the micro-ohmmeter reads “1.” **Cause**: The 100A current loop is not properly connected, or the switch was not closed. **Solution**: Inspect the test leads, reconnect them, and ensure the clamp is securely attached. Then close the switch. 3. **Issue**: The test current appears normal, but the highest digit on the micro-ohmmeter still shows “1.” **Cause**: The voltage clamp is incorrectly positioned, the tested circuit has a resistance higher than 2000Ω, or the voltage signal line is broken or disconnected. **Solution**: Check the voltage signal loop, reposition the voltage clamp, and verify the connections. If the reading is out of range, use a multimeter to measure the voltage between P1 and P2, then divide by the current value to calculate the resistance. 4. **Issue**: The output current is significantly lower than 100A. **Cause**: The power supply voltage is too low, the power cable has high resistance, or there is poor contact. This can result in a voltage drop below 190V during DC output. Additionally, loose connections at C1, C2, P1, and P2 terminals may cause this issue. **Solution**: Use a stable and qualified power source, avoid using excessively long or thin cables, and ensure all terminal connections are tight. Apply proper force when tightening the connectors. 5. **Issue**: The test current is normal, but the micro-ohmmeter reading is abnormal and inconsistent. **Cause**: Poor contact in the voltage signal circuit or instability in the measured resistance itself. **Solution**: Ensure all connections are secure and reliable. Recheck the contact points and eliminate any potential interference. 6. **Issue**: The micro-ohmmeter displays a negative value while the test current is normal. **Cause**: The voltage clamp is misaligned or reversed. **Solution**: Correct the position of the voltage clamp. The correct configuration should be: P1+ and P2-. 7. **Issue**: The displayed value fluctuates during the test. **Cause**: The test leads are inductive and not fully extended. **Solution**: Spread out the test leads to reduce inductance and stabilize the readings. These troubleshooting steps help ensure accurate and consistent performance of the Loop Resistance Tester, making it a reliable tool for electrical maintenance and testing professionals.

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