Residual current circuit breakers (RCCBs) play a significant role in daily life, primarily serving as grounding protection devices to prevent electric shock and accidents caused by leakage current. When the leakage current in a circuit or electrical equipment exceeds the device's set value, or when a person or animal is at risk of electric shock, it can quickly activate, cutting off the power supply to prevent the accident from escalating and ensuring the safety of people and equipment. Below, we will introduce the selection criteria and product characteristics of RCCBs.
What are the specifications of a residual current circuit breaker (RCCB)?
Residual current circuit breakers (RCCBs) effectively protect against indirect and direct electric shocks from low-voltage power grids. They are available in three-phase and single-phase versions. Since the operating value is not determined by the current setting, RCCBs offer highly sensitive protection. So, what are the typical specifications of RCCBs? Here are two models: T1B1-63C16/1T1B1 and T1B1L-63C20/1/0.03. T1B1-63C is a single-product model from the RCCB manufacturer; 20 indicates a 1P type RCCB; and 0.03 indicates an operating current of 30 mA.
I. Selection of Residual Current Circuit Breaker
1. Choose according to the intended use.
(1) Direct contact protection is to prevent electric shock accidents caused by direct contact of the human body with the live conductor of electrical equipment. When the human body is in direct contact with the live conductor, before the leakage current protection device cuts off the power, the electric current passing through the human body is not related to the operating current of the leakage current protection device. It is completely determined by the voltage of the human body and the resistance of the human body. The leakage current protection device cannot limit the electric current passing through the human body. Therefore, the leakage current protection device used for direct contact protection must have a fast action performance of less than 0.1S or have the inverse time characteristic specified in the IEC leakage current protection device standard.
(2) Indirect contact protection is to prevent dangerous contact voltages from appearing on exposed metal parts such as metal casings when insulation damage occurs in electrical equipment. The selection of the operating current I△n of the residual current device (RCD) should be considered in conjunction with the grounding resistance R and the allowable contact voltage U of the electrical equipment. The contact voltage U on the electrical equipment should be less than the specified value. Selection of the operating current I△n of the RCD: I△n≤U/R Where: U——allowable contact voltage R——contact resistance of the equipment Generally, for fixed electrical equipment with a rated voltage of 220V or 380V, such as water pumps, grinding mills, and other electrical equipment that is easily in contact with the human body, when the grounding resistance of the metal casing of the electrical equipment is below 500Ω, a residual current device with an operating current of 30～50mA and an operating time within 0.1s can be selected; when the grounding resistance of the metal casing of the electrical equipment is below 100Ω, a residual current device with an operating current of 200～500mA can be selected; for more important electrical equipment, in order to reduce instantaneous power outage accidents, a time-delay type protection device with an operating current of 0.2s can also be selected. Household electrical appliances often have plugs that are frequently plugged in and unplugged, and some residential buildings lack grounding protection. When an electrical appliance experiences an insulation fault such as leakage current contacting the casing, the casing may exhibit a dangerous voltage equal to the operating voltage, easily leading to electric shock accidents. Therefore, electrical equipment installation regulations stipulate that a highly sensitive residual current circuit breaker with an operating current of 30mA and an operating time of less than 0.1S must be installed after the electricity meter on the incoming power line to the household.
2. Selection based on the usage location: Generally, in 380/220V low-voltage circuits, if the metal casing or other metal parts of electrical equipment are easily accessible, and if the grounding resistance of this equipment cannot meet the requirements of Chinese electrical regulations (less than 4Ω or 10Ω), then a residual current device (RCD) should be installed in the power supply circuit of the equipment according to indirect contact protection requirements. Furthermore, the appropriate RCD with different operating current should be selected based on the specific usage location. For example, in damp workplaces, because the human body is more prone to sweating or getting wet, the insulation performance of the skin decreases, and the body resistance drops significantly. In the event of an electric shock, the current passing through the body will inevitably be greater than in a dry environment, posing a higher risk. Therefore, an RCD with an operating current of 15–30mA and capable of operating within 0.1S is suitable.
II. Characteristics of Residual Current Circuit Breakers
As a special type of circuit breaker, the most significant characteristic of a residual current device (RCD) is its detection and judgment function. Like a circuit breaker, an RCD can disconnect or connect the main circuit, and it also detects and judges whether there is a leakage current in the circuit. If a leakage current is detected in the main circuit, the RCD will activate its detection function, disconnecting or connecting the switching elements in the circuit. Furthermore, RCDs can be used in conjunction with thermal relays and fuses, greatly improving their structural functionality. Currently, this type of device is widely used.
III. Differences between Residual Current Circuit Breakers (RCCBs) and Air Circuit Breakers
Residual current circuit breaker
1. The residual current circuit breaker (RCCB) operates on the live wire. If a person touches the live wire, a circuit is formed between the person and the ground, resulting in an additional current flowing through the non-neutral wire. This will automatically trigger the internal electromagnetic device, causing the RCCB to trip and immediately cut off the power to protect the person.
2. When an air switch has a residual current protection function, it is called a residual current circuit breaker (RCCB). The principle for determining whether there is a leakage current is that the current flowing into and out of the switch must be equal; otherwise, it is considered a leakage current. When the leakage current reaches or exceeds a certain level, a protective action is triggered—the circuit breaker trips.
3. If the purpose is for personal safety protection, a leakage current less than 30mA is considered safe; if it exceeds 30mA, it is considered unsafe and will trigger the protective action. A leakage current protector or circuit breaker with a rated current of 30mA is considered a leakage current protector or circuit breaker of the same sensitivity. Its protective action time should also be within 0.1 seconds.
air switch
1. An air circuit breaker operates on both the neutral and live wires. It will automatically trip when the current between the two wires is too high, functioning like a fuse.
2. An air circuit breaker is used to prevent short circuits or overloads. It will trip if there is a short circuit or overload, but it will not trip if there is a leakage current.
3. An air circuit breaker is a switch that controls the opening and closing of an electrical circuit. If air is used as the arc-extinguishing medium, it is called an air circuit breaker. It is generally selected based on the rated current (load) and used as the main switch for the electrical circuit.
