Leakage protection devices used to prevent electric shock accidents can only be used as additional protection.When installing leakage protection devices, the original safety protection measures shall not be cancelled or abandoned.

The electric leakage protection device is used to prevent the person to be electrocuted and the electric leakage causes the accident one kind of earthing protection device, when the electric leakage current of the circuit or the electric equipment is larger than the device setting value, or the person, the animal produces the electric shock danger, it can move quickly, cuts off the accident power supply, avoids the accident expansion, guaranteed the person, the equipment safety.Therefore, the correct selection and maintenance management of leakage protection switch is the main technology and management measures for rural safe electricity use.

First, the correct selection of leakage protection device

The selection of leakage protection device should be determined according to the protection mode of the system, the purpose of use, the installation site, the voltage grade, the leakage current of the controlled circuit and the grounding resistance value of the electrical equipment and other factors.

1. Choose according to the purpose of use

According to the different requirements of direct contact protection and indirect contact protection, the electric leakage protection device used to prevent electric shock to human body should be selected.

(1), direct contact with the protection is to prevent the human body directly touch the electrical equipment of electric shock caused by electric conductor casualty, when the human body and charged conductor direct contact, before the leakage protective device to cut off the power supply, through the body of the shock current and leakage protection action current choice has nothing to do, it is completely determined by the human body electric shock voltage and the human body resistance, residual current protection device can limit through the body of the shock current, so the leakage protection device for direct contact with the protection, it must be less than 0.1 S rapid movement performance, or with IEC electrical leakage protection device standard inverse time characteristics.

(2) indirect contact protection is to prevent the electrical equipment in the event of insulation damage, exposed metal parts such as the metal shell presents dangerous contact voltage.The choice of the action current of the leakage protection switch I delta n should be considered in connection with the grounding resistance R of the electrical equipment and the permitted contact voltage U, the contact voltage U on the electrical equipment is less than the specified value.Leakage protector of the action current delta n I choice: I delta n U/R or less: U R -- - allows contact voltage equipment general contact resistance for the rated voltage of 220 v or 380 v fixed electrical equipment, such as water pump, grinder and other easy to contact with the human body of electrical equipment, when the metal shell of the electrical equipment grounding resistance under 500 Ω, 30 ~ 50 ma, optional action within 0.1 s of leakage protection device;When the metal shell of the electrical equipment grounding resistance under 100 Ω, can choose the electric leakage protection device of 200 ~ 500 ma;For more important electrical equipment, in order to reduce instantaneous power failure accidents, delay protection device with operating current of 0.2s can also be used.Household electrical equipment is often equipped with a plug that is frequently plugged in and out. At the same time, some residential buildings do not consider grounding protection facilities.When the electrical equipment insulation failure, such as leakage touch shell equipment shell the same dangerous voltage and working voltage may be present, easily happened casualty accident getting an electric shock, therefore, electric equipment installation procedures, must be behind the family line into the homes of watt-hour meter, install the operating current is 30 ma and action within 0.1 S of high sensitive type leakage protection switch.

2. Choose according to the place of use

Generally in 380/220 v low voltage line, if the metal casing of electrical equipment such as metal parts easy to hit, at the same time the electricity equipment and not be in accordance with the requirements for electricity regulation in China make the grounding resistance less than 4 Ω or 10 Ω, criterion appropriate requirement according to indirect contact protection, the power supply circuit of electrical equipment installed in the electric leakage protection device, at the same time also should be used according to different places, reasonably select the different operating current leakage switch.In damp place of work, for example: because the body is easy to sweat or wet, make the skin of the insulation performance, human body resistance decreased obviously, when an electric shock accident, through the body's current must be bigger than dry places, high risk, therefore, is suitable for installation of 15 ~ 30 ma, and can be within 0.1 S action of leakage protection device.

3, according to the normal leakage current of the circuit and electrical equipment to choose

(1) the lower the operating current of the leakage protection device is, of course, it can improve the sensitivity of the switch.However, in any power supply circuit and electrical equipment, insulation resistance cannot be infinite, and there will always be some leakage current.Therefore, from the perspective of ensuring the stable operation of the circuit and providing uninterrupted power supply, the operation current selection of the leakage protection device is restricted by the normal leakage current of the circuit.

(2), as a result of the determination of current leakage current, there must be more complex testing method or the use of special test equipment to measure, convenient for use, can refer to the following empirical formula: for the lighting circuit and residents living power single-phase circuit: I delta n IH / 2000 or more for three-phase three-wire system and three-phase four-wire system power circuit and power and lighting circuit: I delta n IH / 1000 or more among them:I delta n - leakage protection switch device current IH - the actual maximum power supply current average household power supply circuit, if users of 3 a watt-hour meter, normally every around the leakage current of 1 ma, in principle, the leakage current in single-phase circuit in the family less than 1/3000 of the maximum power supply current circuit, the circuit for maintenance.

(3) the insulation level of rural low-voltage power grid in China is low, and the leakage current is large.According to the measured results, there is no significant relationship between the leakage current and the distribution transformer capacity, but there is an obvious relationship between the leakage current and the number of residential households in the low-voltage power grid. That is to say, no matter what the transformer capacity is, the larger the number of households supplying the domestic electricity, the greater the leakage current will be.Therefore, this point should be considered when installing leakage switches in rural power grids.Generally speaking, in order to protect the reliable operation of the power grid and ensure the selectivity of multi-level protection, the operating current of the lower level of leakage protection should be less than the operating current of the upper level of leakage protection, and the operating current of each level of leakage protection should be 1.2 ~ 2.5 times different.The first-stage leakage protection device should be installed at the outlet end of the main line at the low-voltage side of the distribution transformer. The protection line of this stage is long and the superimposed leakage current is large.The maximum leakage operating current shall not exceed 100mA without multistage protection, and 300mA without multistage protection.The second level of leakage protection device should be installed at the outlet end of each branch line. As the protected line is short and the leakage current is relatively small, its leakage operating current should be between the leakage operating current of the upper and lower protection, generally taking 30 ~ 75mA.The third level leakage protection device (also known as the final level protection) is used to protect the safety of electrical equipment and personal, the protected circuit is short, the leakage current is small, generally not more than 10mA, the leakage action current should be selected according to the human body to get rid of the current value (10 ~ 20mA), should not be greater than 30mA, generally take 15 ~ 30mA.