Conducting a contact resistance test is crucial for assessing the quality of electrical connections, especially in circuit breakers, switches, and busbars. Here’s how it’s done:

Step-by-Step Guide to Contact Resistance Testing

1. Prepare Equipment and Setup:

• Use a micro-ohmmeter or contact resistance tester equipped with a four-wire (Kelvin) measurement method. This setup helps eliminate lead and contact resistances, ensuring accuracy.
• Calibrate the equipment if necessary and inspect all components to ensure reliable testing.

2. Connect the Test Leads:

• Attach current leads to each side of the contact or joint you’re testing, which will inject a controlled current.
• Connect voltage leads within the current loop, as close to the contact points as possible, to measure the voltage drop accurately across the connection.

3. Inject Current and Measure Voltage Drop:

• Set the current (typically between 50 to 100 A for power system components) on the tester, and allow the current to stabilize.
• The device measures the voltage drop across the contacts and calculates resistance using Ohm’s Law ($R = \frac{V}{I}$).

4. Account for Thermal EMF:

• Thermal EMFs, caused by temperature differences in metals, can interfere with readings. Many testers counteract this by automatically reversing polarity or averaging readings to minimize errors.

5. Repeat with Higher Current (if necessary):

• If initial readings show high resistance, repeat the test at a higher current. Higher currents can penetrate surface oxidation and contaminants, yielding more accurate measurements.

6. Analyze and Record Results:

• Compare results to previous test data or manufacturer specifications to assess connection integrity.
• High contact resistance may indicate wear, oxidation, or misalignment, signaling the need for maintenance.

7. Perform Trend Analysis:

• Regular testing and trend analysis provide insights into the condition of connections over time, helping prevent failures and ensure reliable operation.

By following these steps, contact resistance testing can effectively identify potential connection issues early, improving the safety and longevity of electrical equipment