Detect Hidden Wire Breaks with AC Voltage!
Description
Portable electrical equipment, such as video cameras, halogen flood lights, electrical irons, hand drills, grinders, and cutters, are typically powered by connecting long 2- or 3-core cables to the mains supply. Due to prolonged operation, the power cord wires are subjected to mechanical strain and stress, which can lead to internal wire fracturing at any point. Consequently, most individuals opt for cable replacement, as pinpointing the exact location of a broken wire is frequently difficult.
In 3-core cables, it’s almost impossible to determine a broken wire and its location without physically disturbing all three insulated wires concealed within a PVC jacket. This circuit enables easy and quick detection of a broken/faulty wire and its break point in 1-core, 2-core, and 3-core cables, without requiring wire manipulation. It utilizes a CD4069 hex inverter CMOS integrated circuit.
Gates N3 and N4 function as a pulse generator that oscillates at approximately 1000 Hz within the audio frequency range. The oscillation frequency is governed by the timing components, namely resistors R3 and R4, and capacitor C1. Gates N1 and N2 are employed to sense the presence of 230V AC voltage surrounding the live wire and buffer the weak AC voltage picked up by the test probe. The voltage at output pin 10 of gate N2 can either enable or inhibit the oscillator circuit.
When the test probe is not in proximity to any high-voltage AC field, output pin 10 of gate N2 remains low. Consequently, diode D3 conducts, inhibiting the oscillator circuit from generating an oscillation. Simultaneously, the output of gate N3 at pin 6 goes ‘low’, thereby cutting off transistor T1. As a result, LED1 remains off. When the test probe is moved closer to the 230V AC, 50Hz mains live wire, during each positive half-cycle, output pin 10 of gate N2 goes high.
Therefore, during each positive half-cycle of the mains frequency, the oscillator circuit is allowed to oscillate at around 1 kHz, causing red LED (LED1) to blink. (Due to the persistence of vision, the LED appears to be continuously glowing.) This blinking reduces the current consumption from button cells used for the power supply. A 3V DC supply is sufficient for powering the entire circuit.
Circuit diagram:
AG13 or LR44 type button cells, which are also used within laser pointers or in LED-based continuity testers, can be utilized for the circuit. The circuit consumes 3 mA during the sensing of AC mains voltage. For audio-visual indication, one may employ a small buzzer (typically found inside quartz alarm time pieces) in parallel with a small (3mm) LCD in place of LED1 and resistor R5. In such a case, the current consumption of the circuit will be approximately 7 mA.
Alternatively, one may use two 1.5V R6- or AA-type batteries. Employing this gadget, one can also swiftly detect fused small filament bulbs in serial loops powered by 230V AC mains. The entire circuit can be accommodated within a small PVC pipe and utilized as a handy broken-wire detector. Prior to detecting broken faulty wires, disconnect any connected loads and determine the faulty wire first by utilizing a continuity method using a multimeter or continuity tester.
Then connect the 230V AC mains live wire at one end of the faulty wire, leaving the other end free. Connect the neutral terminal of the mains AC to the remaining wires at one end. However, if any of the remaining wires is also found to be faulty, then both ends of these wires are connected to neutral. For single-wire testing, connecting neutral only to the live wire at one end is sufficient to detect the breakage point.
In this circuit, a 5cm (2-inch) long, thick, single-strand wire functions as the test probe. To detect the breakage point, switch S1 is turned on, and the test probe is slowly moved closer to the faulty wire, beginning with the input point of the live wire and proceeding towards its other end. LED1 begins to glow when AC voltage is present in the faulty wire. When the breakage point is reached, LED1 immediately extinguishes due to the lack of mains AC voltage. The point where LED1 is turned off represents the precise broken-wire location. While testing a broken 3-core rounded cable wire, bend the probe's edge into a ‘J’ shape to increase its sensitivity and move the bent edge of the test probe closer over the cable. During testing, avoid any strong electric fields near the circuit to prevent false detections.