Cables may experience faults during use, such as cable breakdown, conductor damage, and core breakage. The conductors in flame-retardant cables have a small cross-sectional area and can be pulled apart during the cable manufacturing and extrusion processes. So how can you detect broken conductors in flame-retardant cables?
First: The Capacitance Method
Some cable manufacturers typically use capacitance comparison to locate the approximate location of a broken conductor. This method, which uses continuous current to pinpoint the break, is inefficient. It typically takes about an hour and a half to locate a single break. This method is nearly impossible to locate broken conductors in flame-retardant cables that have already been shielded, armored, and sheathed. Faulty workmanship can even render the cable scrapped. This method is now largely unused.
Second: A Combination of Capacitance and Induction Methods:
This method is used to detect broken conductors in cables that are not covered with a metal coating or extruded sheath. When searching for a cable break, first use a capacitor to locate the approximate location of the break. Then, use the induction voltage method to precisely locate the break. This method is simple, quick, and currently the most commonly used. The induction voltage method involves applying a 650V AC voltage to one end of the broken cable core, while the other end and the rest of the core are grounded. Then, a light-emitting sensor pen is used for testing. When the sensor pen passes over the broken core, the signal changes, allowing the cable break to be precisely located.
Three: Combining a Constant Current Source and a Bridge Method
This method is used on finished cables or metal-coated cable cores. First, a constant current source is used to burn the insulation at the broken core of a flame-retardant cable, causing it to break down. Then, a bridge fault locator is used to precisely locate the fault. This is also a commonly used method.
