No, contact resistance testers are typically designed for use on de-energized (non-live) circuits. Using a contact resistance tester on a live circuit can pose serious safety hazards to both the user and the equipment, and it can also damage the tester. Here’s why contact resistance testing should generally be performed on de-energized circuits, along with alternative methods for live testing if absolutely necessary:

Why Contact Resistance Testers Are Not Suitable for Live Circuits

1. High Current Injection: Contact resistance testers often inject a significant current (ranging from a few amps to several hundred amps) to measure resistance. Applying this current to an energized circuit can lead to erratic measurements, interference, or dangerous electrical faults.

2. Safety Hazards: Measuring resistance on live circuits can lead to electric shock, arc flash incidents, or equipment damage. This is particularly risky when testing high-voltage equipment like circuit breakers and busbars.

3. Tester Damage: The design of most contact resistance testers does not account for handling the voltage present in live circuits. Connecting the tester to an energized circuit can damage internal components, void warranties, and necessitate costly repairs.

4. Measurement Interference: Power running through a live circuit can interfere with the resistance measurement, leading to inaccurate or unstable readings.

Alternative Options for Testing on Live Circuits

While contact resistance testing requires the circuit to be de-energized, here are some alternatives for diagnosing issues in live circuits:

1. Infrared Thermography: Using an infrared camera, you can detect “hot spots” on live circuits. Hot spots often indicate high resistance due to loose, corroded, or worn contacts.

2. Ultrasound Testing: Ultrasonic devices can detect abnormal sounds, like arcing or partial discharge, in live equipment. These sounds often correlate with issues in contact resistance and poor connections.

3. Voltage Drop Testing: If testing on a live circuit is absolutely necessary, voltage drop testing may be used as a rough indicator. By measuring the voltage across a known connection while current flows through it, you can calculate resistance indirectly. However, this is typically less accurate than contact resistance testing and does not directly replace it.

4. Specialized Live-Testing Equipment: Some manufacturers produce specialized equipment for testing specific live circuit parameters safely. However, these tools are generally for detecting voltage drops, partial discharge, or other specific electrical parameters, rather than directly measuring contact resistance.

Best Practices for Contact Resistance Testing

1. De-energize the Circuit: Always isolate and de-energize the equipment before performing contact resistance testing.
2. Use Personal Protective Equipment (PPE): When working on high-power equipment, even de-energized, wear appropriate PPE to guard against residual risks.
3. Follow Lockout-Tagout (LOTO) Procedures: Ensure the circuit is properly isolated from power sources, and secure it with LOTO practices to prevent accidental re-energizing during testing.

In Summary

• No, contact resistance testers should not be used on live circuits due to safety and measurement accuracy concerns.
• For live testing, consider infrared thermography, ultrasound testing, or voltage drop testing as safer alternatives.
• Always de-energize the circuit and follow safety protocols for accurate and safe contact resistance testing.

If you’re unsure whether your application requires live testing, consult the equipment’s manual or a qualified technician.

Nov 15,2024