What are the methods for finding power cable fault points?

During actual maintenance and inspection, the biggest dread for repair technicians is encountering a break in a wire or cable and being unable to locate the break. While we often replace or reroute cables when repairing weak current projects, today we'll discuss technical methods for locating cable breaks! When a cable's internal dielectric breaks, the insulation surrounding it prevents the exact location from being seen. This applies to both high-voltage and low-voltage cables. The typical approach to locating the break is to troubleshoot the problem section by section. For example, if a cable breaks, you can measure at three points: one at each end and the middle. If the break is detected, measure at the midpoint. This helps narrow down the area and quickly locate the break.

So, what are some common methods for accurately locating a break in a wire or cable? How do you locate a break in a wire or cable? Here are a few common methods to help:

1. Multimeter Test
First, connect one end of the broken cable to the live power line and leave the other end unconnected. Set the multimeter to the AC2V setting. Starting at the power connection end of the cable, hold the tip of the black pen while slowly moving the red pen along the insulation of the wire. The voltage displayed on the display should be around 0.445V. If the red pen is moved to a certain point, the voltage displayed on the display suddenly drops to a few tenths of 0.0V, about one-tenth of the original voltage. The break is located about 15cm from this point (the live wire connection end).

2. Inductive Test Pen Test Method
An inductive test pen is a device with an electronic screen that can detect voltage and continuity. First, eliminate any power sources in the cables surrounding the broken cable. Then, connect the broken cable to the live wire. Hold the test pen perpendicular to the wire, press the "Inductive Breakpoint Test" button, and slowly move it forward along the wire. When the AC signal detected by the test pen suddenly disappears, the break is determined to be at that point, with a maximum error of 10cm.

It is important to note that the cables surrounding the broken wire must not be powered. It's important to note that this method isn't a panacea. It's more effective with shorter cables, but less effective with longer cables.

3. Using an Audio Detector
An audio detector uses single-frequency or multi-frequency signals to test line continuity and identify line faults. It can directly locate cables while connected to any switch, router, or PC terminal. Tracing cable routes eliminates the need to peel the cable sheath, making it simple and quick, and it can also pinpoint the location of breakpoints.

4. Cable Fault Tester
This is a comprehensive cable fault detection instrument. It can test for high-resistance flashovers, high- and low-resistance ground faults, short circuits, cable breaks, and poor contact. Equipped with an acoustic locator, it can accurately determine the precise location of the fault. It's particularly suitable for testing power and communication cables of various models and voltage levels.

5. Broken Line Test Method
Connect one end of the wire with the break to the black test lead of a multimeter and the other to the red test lead. Set the multimeter to the 200Ω resistance setting. Bend the cable back and forth at the point most likely to break (such as a frequently bent point). If the multimeter shows intermittent continuity, this is the break. If you're still unsure, start bending the cable from one end until you find the break. This method is suitable for shorter cables.

6. Needle Puncture Test

This method involves inserting a steel needle into the broken cable at intervals. Use a multimeter to measure the continuity between the needle and the cable end to determine the break point.

Under normal circumstances, this method is not recommended as it can damage the insulation and easily cause other problems later in cable use, especially in high humidity environments. This method uses the continuity and disconnection of the cable to identify the break point.

7. Wire Pull Test

This method is also a destructive test method and is generally not used in practice, but it is included here as well. Use pliers to pull the broken wire at the cable end. If the break is near the end, the insulation will easily break. This method is suitable for cables with a break near the end.