Cable burglar alarm should catch "four defenses"
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August 25 09:49:10, 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 streets or the overhead cables in mining areas, theft incidents have been frequent and persistent. This not only disrupts the functionality of public facilities but also poses risks to people's safety, either directly or indirectly. To address this growing problem, many cities have implemented daily inspection systems for their cable networks. Alongside these efforts, they have also introduced cable alarm systems and enhanced security measures in high-risk zones.
The cable anti-theft alarm system works by comparing the fixed impedance value with the actual impedance of the cable. When a section of the cable is cut, the impedance changes significantly. If this change exceeds the set threshold, an alarm is triggered. The concept of the "four defenses" — human defense, soil defense, technical defense, and joint defense — has proven effective in reducing cable theft.
Common technologies used in cable anti-theft include power carrier communication monitoring systems. This method uses existing cables to transmit detection signals, eliminating the need for additional wiring. It is widely adopted due to its ease of installation, concealment, and wide coverage. However, it has limitations, such as not being able to deter thieves or provide video evidence. Integration and systematization remain challenges.
Another approach is the capacitance detection system. It uses a pair of empty cables to short-circuit the terminals, and when a break occurs, the circuit forms a capacitor, triggering an alarm. The frequency of the alarm signal varies depending on where the cable is cut.
Current detection systems monitor whether there is any current flowing through the cable. If no current is detected, an alarm is triggered. However, this method is ineffective in systems where no current is present, such as in subway tunnels or highway ventilation systems. Additionally, it may fail to alert if only part of the cable is cut.
As urban and rural areas become more integrated, the development of buried cable anti-theft systems for streetlights has accelerated. Streetlights are essential for nighttime illumination, and their cables are now often laid underground. Underground installation methods include direct burial, pipe laying, and trenching, all of which carry the risk of theft, leading to economic losses and public disorder.
An ideal buried cable anti-theft system should operate without power during off-hours and function normally when the system is active. It should be capable of communicating multiple lines to the control room via a master device.
For highway power cables, the key requirements of an anti-theft system include availability, reliability, advanced alarm discrimination, and scalability for integration with traffic police systems. These systems must detect abnormal signals accurately and minimize false alarms.
With China's rapid economic growth and increasing urbanization, the wire and cable industry has expanded rapidly. In 2012, the average pass rate of wire and cable products reached 88.2% according to a joint quality inspection by AQSIQ. Despite improved safety and quality, the importance of security and anti-theft systems cannot be overlooked.