What Is a Residual-Current Device?

Residual current refers to the current of each phase (including the neutral line) in the low-voltage distribution line. In general, when an accident occurs on the power side, the current flows from the charged body through the human body to the ground, so that the current I in the main circuit and the line I are not equal in magnitude.At this time, the effective value of the instantaneous vector synthesis of the current is called the residual. Electric current, commonly known as leakage.

Residual current is the leakage current. The instantaneous current flowing through the main circuit of the residual current action protection device is the current effective value.
As the residual current changes, indicating that the insulation of the live conductor to the ground is damaged, the detection of the residual current link is used to start the protective device trip to prevent fire caused by electric shock and grounding arc. ^[1]

The wires in the building are in disrepair for years, and the insulation layer is damaged.

The installation and construction of the conductors in the building are not standardized. For example, if the conductors do not pass through the flame-retardant pipe, they are directly buried in the wall or placed on the truss.

The construction quality of the wire is rough, cutting corners and cutting materials. When the steel pipe is used for threading, the inner wall of the steel pipe scratches the wire insulation layer.

When performing secondary renovations, such as entertainment venues and other public activities, the electric wires are laid randomly, which causes various constructions to be left close to flammable materials;

Improper electrical design, including the user increasing the load at will, causing the conductor to overload and heat up, and the conductor insulation layer to age and fail.

The user internally pulls messy lines, and the installation is extremely irregular.

The circuit is affected by natural conditions, such as the conductor hitting a tree, the wind blowing off the conductor, and the dampness of the air causing the insulation level of the conductor to drop.

Disconnections caused by various artificial damage.

To prevent electrical fires caused by ground faults, the following measures should generally be taken:

(1) Carefully check whether the wiring installation meets the requirements of the electrical installation regulations. For example, the distance between the wires, the distance between the front and rear supports, and the maintenance of the damaged insulation should all meet the safety requirements of the device.

(2) Periodically measure and inspect the insulation of the line. If the measured insulation resistance between line conductors and conductors to ground is less than the specified value, the insulation damage must be treated, and severely damaged conductors must be replaced.

(3) Correctly select a fuse that matches the cross section of the conductor. It is strictly forbidden to replace the melt with other metal wires.

(4) Lines and electrical equipment should be operated under permissible load conditions to prevent leakage or short circuit due to insulation damage caused by long-term overload.

(5) Frequently monitor the operation of the line, and deal with it in time if serious overload is found.

To prevent ground fault fires caused by excessive contact resistance, the following measures can be taken:

(1) When connecting between wires, the relevant regulations must be implemented.

(2) The connection of wires with various electrical equipment, especially the connection of aluminum wires with electrical equipment, shall be performed in accordance with the relevant regulations.

(2) Periodic inspections of the running circuits and equipment should be conducted in time if the joints are found to be hot or loose.

Effective measures to prevent electrical fire caused by arcing ground fault

General low pressure

Residual current operated protector

Self-investment in Rural Network

Residual current electrical fire monitoring detector

In order to effectively curb electrical fires, according to the characteristics of electrical fires, the state has formulated "GB14287.2-2014 Electrical Fire Monitoring System Part Two: Residual Current Type Electrical Fire Monitoring Detectors" and the high-rise civil building design code GB50045-95 explained "GB50045", residual current type electrical fire monitoring detector is designed to detect the residual current in electrical circuits to prevent electrical fires. According to relevant regulations, the residual current monitoring of the entire power supply line is generally divided into 3 levels: the main line, the secondary line and the load terminal.

In practical applications, residual current electrical fire monitoring detectors are used in conjunction with residual current action protectors (RCDs). Residual current action protectors are generally installed at the load terminal. They are mainly used to cut off the power supply in time when an electric shock occurs to prevent electric shock. Residual current electrical fire monitoring detectors are installed at the power distribution room and distribution box to detect the residual current of the mains and secondary trunks in real time. If the residual current alarm value is exceeded, an audible and visual alarm signal is immediately issued to prompt maintenance. To prevent electrical fire caused by leakage. The combination of the two can form a complete protection system for "overall monitoring and local tripping" of leakage. It is not suitable to install residual current action protectors in places where large-scale power outages caused by cutting off the overall or mains power supply may cause significant economic loss and adverse social impact. Instead, residual current electrical fire monitoring detectors should be installed.