Cable burglar alarm should catch "four defenses"
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August 25 09:09:00, 2025
In recent years, the theft of cables has become a serious issue, affecting both urban infrastructure and public safety. Whether it's the streetlight cables in city areas or the overhead cables in mining zones, theft has been on the rise, causing disruptions to essential services and even endangering lives. To combat this, many cities have implemented daily inspection systems for power lines. In addition to setting up cable alarm systems, they’ve also strengthened measures in high-risk areas.
The cable anti-theft alarm system works by comparing the fixed impedance value with the actual impedance of the cable. When someone cuts through a section of the cable, the impedance changes. If the change exceeds the pre-set threshold, the system triggers an alarm. This system is part of the "four defenses" strategy—human defense, soil defense, technical defense, and joint defense—which together help reduce cable theft effectively.
There are several common technologies used in cable anti-theft systems. One of the most widely adopted is the power carrier communication monitoring system. This method uses the existing cable as a medium to transmit detection signals. If the signal is interrupted due to a cut, the system automatically alerts the control center. This approach is cost-effective, easy to install, and covers a wide area. However, it doesn't deter criminals directly and lacks video evidence, which limits its effectiveness in investigations.
Another method is the capacitance detection system. It involves using a pair of empty cables to short-circuit the terminals and connect them to an oscillator. Normally, the oscillator doesn’t produce a signal. But when a cable is cut, it acts like a capacitor, triggering the alarm. The frequency of the signal varies depending on where the cut occurs.
The current detection system monitors whether there is any current flowing through the cable. If no current is detected, the system sounds an alarm. However, this method isn’t suitable for low-current environments, such as subway tunnels or highway ventilation systems. Also, it only triggers an alarm if all branches of the circuit are cut, leading to potential “non-reporting†issues.
As urbanization continues, the need for effective buried cable anti-theft systems is growing. Streetlight cables, now mostly laid underground, face significant risks of being stolen, resulting in economic loss and public disorder. An ideal system should operate without power during off-hours and remain active during normal operation, independent of the cable length or lamp model. Communication between multiple lines and the control room is also crucial.
For expressways, where power cables are critical, the anti-theft system must be reliable, accurate, and scalable. It should integrate with traffic management systems and minimize false alarms. Advanced discrimination features are necessary to distinguish between normal and abnormal conditions.
With China’s rapid economic growth and industrial development, the wire and cable industry has expanded significantly. According to a 2012 quality inspection report, the pass rate for cable products reached 88.2%. Despite these improvements, security and anti-theft systems remain vital to protect valuable infrastructure from theft and damage.