The circular residual current transformer features an integrated, closed-loop structure and a high-permeability core, enabling precise detection of minute residual currents (at the milliampere level) with stable signal output and strong interference resistance. The product series offers a wide range of aperture sizes to accommodate various cable diameters and busbar dimensions.
1. High-Sensitivity Zero-Sequence Detection
Utilizing a high-permeability core material, the device features a continuous magnetic circuit without air gaps and excellent magnetization curve linearity. It accurately identifies milliampere-level residual current signals with high sensitivity and low error rates, effectively preventing both false alarms and missed detections. With strong resistance to external electromagnetic interference, it maintains stable, accurate signal output even in complex distribution environments, providing reliable data for earth leakage protection and fire early warning systems.
2. Integrated Closed-Loop Structure
The unit employs a closed-loop ring design with a continuous magnetic circuit, offering superior measurement accuracy and stability compared to split-core (openable) designs. The housing is injection-molded from high-strength, flame-retardant engineering plastic, while the interior is sealed with epoxy resin potting. This ensures resistance to moisture, dust, and aging, resulting in minimal thermal drift and consistent performance during long-term operation—making it ideal for continuous use within power distribution cabinets.
3. Comprehensive Aperture Range
A wide variety of aperture sizes is available, ranging from small-bore models for branch circuits to large-bore models for main incoming lines. They accommodate diverse wiring requirements, including single small-gauge cables, multiple large-gauge cables, and rectangular busbars. Suitable for all levels of the distribution network—from terminal branches to main incoming cabinets—the series offers flexible selection to meet specific installation needs across different projects.
4. Base-Mounted Design
The product features an integrated mounting base, allowing for quick and secure screw-fastening within power distribution cabinets, ensuring a stable, wobble-free installation. Features side-mounted standard terminals with clear labeling for simple, convenient wiring. It is directly compatible with mainstream electrical fire monitoring detectors, earth leakage relays, and fire monitoring control panels—eliminating the need for extra adapters and significantly boosting installation and commissioning efficiency.
Select the transformer model with the appropriate aperture size based on the specifications and quantity of cables in the circuit being monitored;
Pass all live conductors (phase lines + neutral line) of the circuit through the transformer aperture in the same direction; strictly ensure the protective earth (PE) wire does not pass through;
Use screws through the mounting base to secure the transformer horizontally onto a mounting beam or insulating board within the power distribution cabinet;
Connect the secondary output wires to the monitoring detector or protection device according to the terminal polarity markings, ensuring all connections are secure.
For three-phase four-wire circuits, all three phase lines and the neutral line must pass through the aperture simultaneously and in the same direction; for single-phase circuits, both the phase line and neutral line must pass through together; otherwise, residual current cannot be detected correctly;
Ensure reliable contact for secondary-side wiring and avoid open-circuit operation; prevent strong impacts or crushing during installation to avoid damaging the magnetic properties of the iron core;
Designed for indoor cabinet installation; additional waterproofing measures are required for outdoor or humid environments.
Electrical Fire Monitoring Systems: Real-time residual current monitoring and threshold-based alarms for distribution circuits at all levels; prevents electrical fires and ensures compliance with fire safety regulations;
Low-Voltage Earth Leakage Protection Systems: Pairs with earth leakage relays to trip circuits upon detecting leakage faults, preventing electric shock hazards to personnel;
Fire Power Supply Monitoring Systems: Monitors residual current and operational status of dedicated fire safety distribution circuits, ensuring reliable power supply for fire safety equipment;
Industrial Power Distribution Safety Monitoring: Detects leakage in factory production lines and power equipment circuits, identifying insulation aging risks early;
Smart Building Power Distribution: Provides leakage warnings and supports safe operation and maintenance for power distribution systems in commercial complexes, office buildings, and residential communities.
The entire series of circular residual current transformers is designed and manufactured in strict accordance with relevant national standards. Each unit undergoes multiple tests—including accuracy calibration, power-frequency withstand voltage, and insulation performance checks—before leaving the factory to ensure stable and reliable performance. Supports non-standard customization; parameters such as inner bore dimensions, transformation ratios, and output signals can be adjusted to meet specific requirements.
A professional technical team provides guidance on model selection and post-sales technical support.
Includes a one-year warranty, ensuring product quality.
Project Name: Electrical Fire Monitoring System Retrofit for the "Chengdong Times Square" Commercial Complex
Location: A prefecture-level city in East China
Commissioning Date: June 2025
Products Used: Full range of circular residual current transformers (zero-sequence current transformers)
Built in 2012, this commercial complex has a total floor area of approximately 72,000 m², comprising a basement-level supermarket and four floors of retail and dining areas, with a total of 326 power distribution circuits. Due to its age, the original distribution system lacked standardized residual current monitoring devices; it relied solely on the main incoming circuit's earth-leakage circuit breaker (ELCB) for fault tripping, making it impossible to provide early warnings or pinpoint fault locations.
During the 2024 rainy season, the mall experienced multiple unexplained main-breaker trips due to earth leakage. Troubleshooting required cutting power to circuits one by one for testing—taking over four hours per incident—which severely disrupted normal business operations. Additionally, local fire authorities noted during an annual inspection that the project failed to meet the mandatory requirements of GB 14287.2-2014 (Electrical Fire Monitoring Systems – Part 2: Residual Current-Type Electrical Fire Monitoring Detectors) and mandated corrective action within a specified timeframe.
Consequently, the project owners initiated a comprehensive retrofit of the electrical fire monitoring system in 2025. Circular residual current transformers were installed on all low-voltage distribution output circuits, integrated with electrical fire monitoring detectors and a backend monitoring system, enabling real-time residual current monitoring, threshold-exceedance alerts, and fault localization across all circuits.
Lack of tiered residual current monitoring; inability to provide early warnings for potential hazards. The original system provided earth-leakage protection only at the main incoming line, with no residual current sensing devices on branch circuits. Hazards such as insulation aging and equipment leakage could not be detected early; issues were only identified once a fault escalated to the point of tripping the breaker, resulting in a significant lag in hazard prevention and control. Hidden leakage faults are difficult to locate, resulting in extremely low troubleshooting efficiency. Shopping malls feature numerous power distribution circuits and complex wiring; when a leakage fault occurs, troubleshooting requires cutting power to circuits one by one. A single fault takes over four hours to resolve on average. Frequent power outages severely disrupt store operations, and food and beverage tenants have repeatedly suffered losses due to ingredient spoilage.
Non-compliance with fire safety acceptance standards poses regulatory risks. Current fire safety regulations mandate the installation of residual current-based electrical fire monitoring devices in densely populated commercial venues. The original system lacked this function—a critical defect for fire safety acceptance—creating a risk of forced closure for rectification.
Aging wiring exacerbates leakage risks. The building has been in operation for over a decade, and the insulation on some cables has aged or suffered moisture damage. The risk of leakage is particularly acute in the underground supermarket area due to high humidity, creating a potential fire hazard.
To ensure full circuit coverage, six specifications of circular residual current transformers (based on inner diameter) were selected, tailored to the cable specifications and load types of different circuits. Core design principles include:
Zero-sequence measurement principle: All phase lines and the neutral line pass through the transformer's aperture in the same direction. Under normal operation, the vector sum is zero; when leakage occurs, the residual current induces a signal that is transmitted to the monitoring detector.
Tiered alarm thresholds: The alarm threshold is set to 300mA for terminal circuits and 1A–2A for trunk circuits, balancing the need to prevent false alarms with the sensitivity required for early fault warning.
Flame-retardant insulation design: The transformer housing is made of high-temperature resistant, flame-retardant material suitable for the enclosed, high-temperature environment inside power distribution cabinets; insulation performance meets low-voltage electrical safety standards.
Standardized installation: Units come with an integrated mounting base for screw-fixing inside distribution cabinets; terminals feature a standard plug-in design, ensuring convenient installation and secure connections.
Comprehensive specification coverage for diverse cabling scenarios: The selection ranges from small-bore (φ25mm) to large-bore (φ200mm) models, perfectly accommodating every circuit from lighting branch lines to main incoming lines. Standardized supply eliminates the need for custom manufacturing, thereby shortening the construction period. Stable measurement accuracy and low false alarm rate: Utilizing a high-permeability toroidal core with evenly distributed windings ensures excellent linearity in residual current measurement and accurate detection of low-current signals. Post-commissioning data shows an alarm accuracy rate exceeding 96%, with no instances of frequent false alarms disrupting normal power usage.
Convenient installation with minimal power interruption: The feed-through design combined with a base-mount fixture allows installation by powering down only the specific circuit being addressed; the average installation time per transformer is approximately 15 minutes. The entire project was completed in just 12 days—well ahead of schedule—minimizing the impact on the shopping mall's business operations.
Flame-retardant and high-temperature resistant, suitable for harsh cabinet environments: The housing is made of flame-retardant engineering plastic, while the core and windings are encapsulated in epoxy resin for moisture protection. The unit maintains insulation performance and measurement accuracy without degradation during long-term operation in the enclosed, high-temperature (above 40°C) environment of power distribution cabinets.
Integration with backend systems for visual O&M: Transformer output signals feed into electrical fire monitoring detectors and aggregate at the fire control room's backend system. This enables real-time monitoring of residual current values for each circuit; if limits are exceeded, an automatic pop-up alarm displays the specific circuit location, allowing O&M personnel to pinpoint the fault immediately.
Successfully passed specialized fire safety acceptance inspection: Following the retrofit, the system passed the local fire rescue agency's specialized acceptance inspection for electrical fire safety. Residual current monitoring functions, alarm logic, and graded protection schemes all comply with the GB 14287 standard, fully resolving previous compliance issues.
Significantly improved fault early warning and localization efficiency: By the end of 2025, the system had issued early warnings for 27 instances of excessive residual current (19 caused by insulation faults in tenant equipment and 8 by moisture or aging in wiring). O&M personnel can pinpoint faults directly based on the alarmed circuit; the average troubleshooting time was reduced to under 20 minutes, representing an 85% increase in efficiency.
Closed-loop management of electrical fire hazards: All leakage hazards were rectified before any circuit tripping occurred. Since the retrofit, there have been no unplanned power outages caused by leakage, and moisture-related leakage risks in the underground supermarket area have been effectively controlled, resulting in zero electrical safety accidents throughout the year. Operational and maintenance costs are significantly reduced; there is no need for manual, circuit-by-circuit troubleshooting of leakage faults, thereby minimizing merchant losses caused by power outages and cutting down on manual inspection expenses. The equipment operates stably with no damage or signal drift, requiring minimal maintenance.
The circular residual current transformer serves as a core sensing component in electrical fire monitoring systems and is widely applicable to various low-voltage power distribution environments, including commercial buildings, residential complexes, industrial facilities, and municipal venues. Utilizing the feed-through zero-sequence measurement principle, it accurately detects minute leakage signals within circuits, enabling the early detection, warning, and remediation of potential electrical fire hazards.
Through comprehensive model selection, standardized installation, and systematic integration, this project has demonstrated the high adaptability and reliability of circular residual current transformers in the renovation of aging commercial complexes, proving them to be essential components for upgrading fire safety in low-voltage power distribution systems.
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