Leakage current action protector is referred to as leakage protector, also known as leakage protection switch, mainly used in the equipment when leakage failure and fatal danger of personal shock protection.

Leakage protection is a relatively new technology in the field of electrical safety. In the past 30 years, with the development of electronic technology, the high sensitivity and fast action leakage protection device has been greatly developed. Germany, France, the United Kingdom, the United States, Japan and even the international electrotechnical commission have established and revised the product standards and related standards and regulations of leakage protection devices. In China, there are many manufacturers of leakage protection devices with a wide range of products. The state has formulated the national standard leakage current action protector (gb6829-86), which clearly stipulates the characteristics, classification, working conditions and installation conditions, structure and performance requirements, test methods and inspection rules of leakage protection devices.

I. principle and composition of leakage protector

Leakage protector in response to shock and leakage protection has a high sensitivity and fast action, which is other protective appliances, such as fuses, automatic switches, etc., can not be compared. When the automatic switch and fuse are normal, they should pass the load current, their action protection value should avoid the normal load current to set, so their main function is to cut off the system between short circuit fault (some automatic switch also has overload protection function). And leakage protector is the use of residual current response and action in the system, the normal operation of the system of the residual current is almost zero, so it's the set values for the action to be setting is small (typically for mA level), personal electric shock occurs when the system or equipment shell charged, appear larger residual current, leakage protector, by detecting and processing after the residual current movements in a reliable way, cut off power supply.

So how do leakage protectors protect?

We know that electrical equipment leakage, will present abnormal current or voltage signal, leakage protector through the detection and processing of this abnormal current or voltage signal, prompting the actuator action. We call the leakage protector according to the action of fault current the current type leakage protector, the leakage protector according to the action of fault voltage the voltage type leakage protector. Due to the complex structure of voltage type leakage protector, the poor stability of its operation characteristics due to external interference, and the high manufacturing cost, it has been basically eliminated. At present, the research and application of leakage protector at home and abroad are dominated by current leakage protector.

The current leakage protector is a part of the zero sequence current in the circuit (usually called residual current) as the action signal, and most of the electronic components as the intermediate mechanism, high sensitivity, complete function, so this protection device has been more and more widely used.

Ii. Classification of leakage protector

Leakage protector can be classified according to its protection function, structural characteristics, installation mode, operation mode, pole number and line number, action sensitivity, etc., here mainly by its protection function and purpose classification described, generally can be divided into leakage protection relay, leakage protection switch and leakage protection socket three.

1. Leakage protection relay refers to the leakage protection device that has the function of detecting and judging the leakage current, but does not have the function of cutting off and connecting the main circuit. Leakage protection relay is composed of zero sequence transformer, tripping device and auxiliary contact of output signal. It can be combined with the automatic switch of large current to act as the overall protection of the low-voltage network or leakage, grounding or insulation monitoring protection of the trunk road.

When there is leakage current in the main circuit, the secondary contact and the separation trip of the main circuit switch are connected in series to form a primary circuit. Therefore, the auxiliary contact is connected with the detactor and the air switch and ac contactor are disconnected, so as to make the switch off and cut off the main circuit. The auxiliary contact can also be connected to the acoustic and optical signal devices to send out the leakage alarm signal, reflecting the insulation status of the line.

2. Leakage protection switch refers to the switch elements that can not only connect or disconnect the main circuit like other circuit breakers, but also have the function of detecting and judging the leakage current. When electricity leakage or insulation damage occurs in the main circuit, the leakage protection switch can connect or disconnect the main circuit according to the judgment result. It can be used with fuse and thermal relay to form low-voltage switch elements with perfect function.

At present, this form of leakage protection device is the most widely used, the leakage protection switch on the market according to the function of the commonly used have the following categories:

(1) it only has the function of leakage protection and power failure, and it must cooperate with fuse, thermal relay, overcurrent relay and other protection elements.

(2) it also has overload protection function.

(3) it also has overload and short circuit protection functions.

(4) it also has short-circuit protection function.

(5) it also has the functions of short circuit, overload, leakage, overvoltage and undervoltage.

3. Leakage protection socket refers to the power socket with leakage current detection and judgment and can cut off the circuit. Its rated current is generally less than 20A, leakage action current 6 ~ 30mA, high sensitivity, often used for the protection of hand-held power tools and mobile electrical equipment and home, school and other civilian places.

Three, leakage protection device selection principles

In order to standardize the correct use of leakage protector, the state has promulgated the "leakage protector safety supervision provisions" (laoan word (1999) no. 16) and "leakage protector installation and operation (gb13955-92) and a series of standards and provisions.

According to these standards and regulations, we should follow the following main principles in the selection of leakage protector:

1. When purchasing leakage protector, the products of qualified manufacturers should be purchased, and the product quality inspection is qualified. Here to remind everyone: there are many leakage protectors sold on the market are not qualified products. On October 28, 2002, aqsiq announced the results of spot check on the product quality of leakage protector. About 20% of the products were unqualified. Some do not have the protection of electric shock; Some should not trip when tripping, affecting normal electricity.

2. The power supply voltage, working current, leakage current, operation time and other parameters of the leakage protector shall be determined according to the protection scope, personal equipment safety and environmental requirements.

3. When the power supply adopts leakage protection device for graded protection, it should meet the selectivity of upper and lower switch actions. Generally, the rated leakage current of the upper level leakage protection device is not less than the rated leakage current of the lower level leakage protection device, so as to protect the safety of human and equipment sensitively, and avoid overstep tripping, and narrow the scope of accident inspection.

4. Portable power tools (except class III), mobile household appliances (except class III), other mobile electromechanical equipment, and electrical equipment with greater risk of electric shock, must be installed with leakage protection devices.

5. Electric leakage protectors shall be installed in construction sites and temporary lines. This is explicitly required in the technical specification for temporary electricity safety at construction sites (jgj46-88).

6. Power leakage protectors must also be installed in the power outlet circuits in the offices, schools, enterprises and residential buildings, and in the guest rooms of hotels, restaurants and guest houses.

7. Installed in the power lines and equipment in the water and damp, high temperature, metal occupies larger coefficient and other conductive good places, such as machinery, metallurgy, textile, electronics, food processing industries of workplaces, and the boiler room, water pump room, dining room, bathroom, hospitals and other places, you must use the leakage protector for their own protection.

8. Power distribution box with leakage protector shall be used for electric equipment of fixed lines and normal production and operation places. Temporary use of small electrical equipment, should choose leakage protection plug socket or with leakage protection socket box.

9. When the leakage protector is used as the supplementary protection of direct contact protection (it cannot be used as the only direct contact protection), the leakage protector with high sensitivity and quick action should be used.

In the general environment, the action current should not exceed 30mA and the action time should not exceed 0.1s. These two parameters ensure that if the human body is electrocuted, the electrocuted person will not produce pathological physiological dangerous effects.

The rated action current of the leakage protector in the bathroom, swimming pool and other places should not exceed 10mA.

In the case of possible secondary accidents after electric shock, leakage protection device with rated action current of 6mA should be used.

10. For the electrical equipment that is not allowed to be cut off, such as the passageway lighting in public places, emergency lighting, power supply of fire fighting equipment, power supply for anti-theft alarm, etc., alarm leakage protection device should be selected to connect the sound and light alarm signal, notify the management personnel to deal with the fault in a timely manner.

Installation of leakage protector installation of leakage protector

In addition to following the general installation rules for electrical equipment, the following points should be noted:

1. The installation of leakage protector should meet the requirements of the manufacturer's product manual.

2. The leakage protection device marked with the power side and the load side shall not be connected in reverse. If connected in the opposite way, the trip coil of the electronic leakage protector cannot be cut off with the power supply, so that the power supply will burn up for a long time.

3. When installing the leakage protector, the original safety protection measures shall not be removed or abandoned. The leakage protector can only be used as an additional protection measure in the electrical safety protection system.

4. When installing the leakage protector, the neutral line and the protection line must be strictly distinguished. When using three-pole four-wire and four-pole four-wire leakage protectors, the neutral line should be connected to the leakage protectors. The neutral line passing through the leakage protector shall not be used as the protection line.

5. The working zero line shall not be repeatedly grounded on the load side of the leakage protector, otherwise the leakage protector cannot work normally.

6. If the branch of leakage protection device is adopted, the working zero line can only be used as the zero line of this circuit. It is forbidden to connect with the working zero line of other circuits.

7. After the installation is complete, according to the construction of electrical engineering construction quality acceptance specification clause 3.1.6 (GB50303-2002), the "power and lighting engineering leakage protector should be" do simulation test requirements, the completion of the leakage protector testing, to ensure its sensitivity and reliability. Trial operational test button three times, loading points three times, confirm the action is correct, before officially put into use.

Operation of leakage protector

The safe operation of leakage protector depends on a set of effective management system and measures to ensure. In addition to regular maintenance, the leakage protection device should also be regularly on the action characteristics of the test (including leakage action value and action time, leakage no action current value, etc.), do a good record of the detection, and the initial installation of the value compared with the value to determine whether there is a change in its quality.

In use, the leakage protector should be used according to the requirements of the operation manual and checked once a month according to the regulations. That is, the test button of the leakage protector should be operated to check whether it can normally disconnect the power supply. During the inspection, it should be noted that the time of operation of the test button should not be too long. Generally, it is advisable to move the button by clicking, and the number of times should not be too much to avoid burning the internal components.

When the leakage protector trips in use, if the reason for the switch action is not found after inspection, it is allowed to try to transmit electricity once. If it trips again, the reason should be found out and the fault should be found out.

Once the leakage protector is damaged and cannot be used, it should be immediately checked or replaced by a professional electrician. Electric leakage protector, commonly known as "shock protector" or "life saver", a lot of people think, as long as the installation of leakage protector, you can put an end to the occurrence of electric shock casualties. In fact, a lot of reasons will cause leakage protection device refused to jump, so there is no protection. Therefore, it is very important to fully analyze the reason of the leakage protection device to avoid jumping, and correct the mistake of people's thinking and understanding, so as to prevent the occurrence of electrocution accidents.

5.1 the leakage protector cannot protect under the abnormal running state

5.1.1 internal failure or damage of leakage protector

Although the electric power department of the leakage protection of the management of the relevant system, such as: leakage protection of the agricultural network, generally require rural electrician to check by the cycle jump, but even so, still can not avoid the leakage protection (especially the agricultural network three-phase leakage protection) at any time the possibility of internal failure. If not timely found and troubleshooting, leakage protector will not play due protection. In order to avoid unnecessary legal liability caused by accidents on the agricultural network lines, it is suggested that the responsibility of the agricultural network leakage protection device to the person, to check frequently, and make a good record of running trial jump.

5.1.2 the leakage protector should be manually withdrawn from operation

For some reason, leakage protector misoperation or frequent tripping, individual users in order to coveting convenience, unauthorized leakage protector will be out of operation, so that leakage protector plays less than the due protection. The way to exit the leakage protector operation, in addition to the common way to untie the leakage protector's inlet and outlet line, directly connect it, there is a more concealed and worse way to loosen the leakage protector's internal current coil secondary side of the wiring screw.

5.1.3 wrong connection of leakage protector

Before installing the leakage protector, it is necessary to know its nameplate and operation manual in detail. According to the actual situation on the site, different wiring methods should be adopted. After the installation, be sure to carry out the following inspection :(1) with the load off, off the switch three times, not the wrong action; (2) test with the test button three times, should be able to break correctly; (3) each phase shall be grounded by the test resistance for three times and shall be operated correctly. Only after the above inspection items are qualified, can determine the leakage protector wiring is correct.

Leakage protector installed in TN system, it is important to pay special attention to the distinction between neutral and protective line, three phase four wire type or four pole leakage protector in the neutral wire should be connected to the leakage protector, after leakage protector of neutral line shall not be used as protection, shall not repeat grounding, or pick up equipment exposed conductive parts, protection line shall not be connected to the leakage protector.

5.2 the leakage protector is in normal operation and cannot protect

5.2.1 in TT system, the neutral ground wire of the transformer is disconnected, resulting in single-phase electric shock, and the leakage protector does not work.

When the neutral ground wire of the transformer in the TT system is disconnected, the total leakage protector installed on the load side of the transformer will repeat the following situation: when the trial jump button is pressed, the trial jump is normal, but the leakage protector refuses to jump when the relative short circuit (i.e. single-phase electric shock accident) occurs. The reason for this situation is that the test jump button can only detect whether the leakage protector itself is normal, and after the grounding wire of the transformer's neutral point is disconnected, the short-circuit current cannot flow back to the distribution transformer through the protected line and the ground, so the leakage protector cannot operate.

The above situation should especially cause the attention of the agricultural power management personnel, because many agricultural power management personnel always think: as long as the leakage protection device trial jump is normal, can play a protective role. Especially in recent years the transformer grounding wire stolen shear is quite serious, so it should strengthen the inspection, take extended grounding bar and other technical means. In the normal case of the leakage protector test jump, but also with the grounding resistance grounding test.

5.2.2 in case of phase zero or phase electric shock, the leakage protector will not operate

When the body contact phase zero (or phase), the body resistance is equivalent to a load, while the people are standing on the earth, but through the body electric shock after the electricity flows through the shunt, the vast majority of the phase zero (or phase) wire forming circuit, and get an electric shock electricity flows through the land back to the distribution transformer is few, the electric current cannot make leakage protector action.

According to gb6829-86 "leakage current action protector", "leakage protector cannot protect against the danger of electric shock caused by the simultaneous contact with two lines of the protected circuit".

5.2.3 the leakage protector tripping step by step and cannot operate

In the implementation of graded protection, if the leakage protector has only the action current level difference, but no action time level difference, it is easy to cause the phenomenon of step over gate. The damage of overstep gate is to enlarge the scope of power failure.

5.2.4 the neutral fuse of the knife switch before the leakage protector fuses off and the leakage protector does not work

If the leakage protector is installed together with the switch, the power supply inlet line enters the switch first and then the protection switch. When the neutral fuse of the switch is fused, the leakage protector's "own circuit" will push the working power supply, and it cannot work. At this point, if the phase line fuse is not refreshed, all kinds of electrical appliances have stopped working, but the following line is still live, forming a "false" power failure. When the user USES the electrical appliances or check the "false" power failure, the leakage protection device because of the loss of power refused to move and prone to electric shock accidents. In order to make the leakage protector can give full play to its due role, it is suggested that the users who adopt this connection mode should remove the neutral fuse in the switch and replace it with the same specification of wire.

Electric leakage protection device is not "life-saving device", many reasons can cause it to refuse to jump, the majority of agricultural electricity workers and users should have a clear understanding, to prevent a moment of carelessness, resulting in the occurrence of electrocution accidents.

And to residential electricity should be installed leakage switch, there are the following several wrong views, leakage switch will occur wrong action, resulting in power failure, so do not install leakage switch; As long as the grounding is reliable, can not install leakage switch, has been installed leakage switch, the electrical equipment shell is not connected to the grounding does not matter; Has installed the leakage switch, and then the electrical equipment shell and the water pipe connected, how tunnel; Already installed leakage switch, electrical equipment is grounded also, the toilet that contains bath crock need not make local and so potential connection again. The following is an analysis of each of the above errors.

1. Tripping of leakage switch can be divided into normal tripping and abnormal tripping.

Normal trip shows that: if the rated leakage action current is 30MA leakage switch, the load of the leakage current more than 25MA, leakage switch will trip. Since the current of 25MA is safe to flow through the human body, death by electric shock will not occur; Similarly, there is no danger to the line or electrical equipment, and the work of the electrical equipment will not produce abnormal phenomena. In this case, do not add analysis, mistakenly think that there is a problem with the quality of the leakage switch, arbitrarily remove the leakage switch, is extremely wrong, after the removal of the leakage switch, see the electrical equipment is working normally, think that the dismantling is right, this is a dangerous practice.

Abnormal trip is caused by the leakage switch itself is not qualified, divided into two categories; Unable to close and sometimes trip for no reason. In the case of leakage switch connected to the power supply and not connected to the load, if not close, must be the quality problem of leakage switch, do not repair themselves, because after the repair must carry out technical performance test after the test can be set into use, no test equipment after the use is not safe. The second type is the occasional trip, especially in the middle of the night trip or no one at home trip, this trip shows that the leakage switch anti-interference performance is poor. The leakage switch with abnormal trip should be removed and replaced with a good leakage switch.

If the leakage current of normal tripping fluctuates above and below 25MA, the phenomenon is similar to that of occasional tripping, which is often caused by aging insulation of wires, that is, tripping when the environment is wet and not tripping when the environment is dry. A reliable way to distinguish between such normal tripping and occasional tripping is to measure the insulation resistance of lines and electrical equipment. Standard regulation, each wire insulation resistance shall be not less than 0.5 M Ω, electrical equipment insulation resistance is generally greater than 0.5 M Ω. If the leakage switch after the load, the total measuring insulation resistance is less than 8.8 K Ω Ω (220 v / 25 ma = 8.8 K), so normal trip will occur.

It is, of course, wrong to regard the normal trip as a misoperation of the leakage switch and not to install the leakage switch. Because once the leakage expands beyond 30MA, there's a risk of an electric shock.

Grounding of electrical equipment is the basic measure of electricity safety. However, even if the grounding resistance of the grounding pole meets the requirements, the grounding reliability of the electrical equipment cannot be guaranteed. Residential electrical equipment within the earth wire is not more than 2.5 was, from the main grounding, grounding, grounding feeder to electrical equipment, there is a lot of points, with a little connection is unreliable or fracture, especially the grounding socket pile head poor contact, can cause ground unreliable, so can't guarantee the electrical equipment grounding is absolutely reliable, reliable grounding, or only guarantee measurement inspection can guarantee always reliable. Therefore, there are other measures to increase the safety of electricity, leakage switch is a very effective method.

3. The housing built in the past is not attached importance to the connection to the ground. Although many families have three-hole sockets, they only have two wires and lack the grounding wire. In order to use electricity safely, each installation leakage switch. Installed after the leakage switch, once appear, leakage, switch trip immediately, to avoid the risk of electric shock, in this case, some people think that the earth wire increase too much trouble, with leakage switch is safe, can not increase the ground wire, this view is wrong, because the leakage switch also has the possibility of failure, with the ground wire, can increase the degree of safety.

4. Up to now, there are still many families to the water pipe as a grounding line, which is not reliable, one is the grounding resistance can not be guaranteed, the second is the fault voltage is very easy to spread along the water pipe. Shanghai television has reported a shikumen housing, the tap of the water is one example; In an analysis of electrocuting reported in electricity world magazine, an elderly woman was electrocuted to death while touching a tap from which electricity was transmitted. Grounding construction is an important hidden work, must be professional team construction, supervision and acceptance. Grounding and installed leakage switch, is not a one-time thing, the grounding resistance of the grounding device should be re-tested once a year, the connection of the grounding wire is reliable, also must be checked frequently.

5. Gb50096-1999 "residential facilities specification" 6.5.2 provisions: toilet should do local equipotential connection. The electrical resistance of the human body can be ignored in the case of complete wetting, such as soaking in a bathtub. In this case, the voltage of electric shock hazard is not regulated in China. According to the IEC, the voltage shall not exceed 12V, while in Japan, the voltage shall not exceed 2.5v. If you don't make equipotential connection, so the risk of low voltage is extremely easily, between the grounding line and neutral line voltage is often more than 10 v, if light neutral line and water pipe short circuit, floodlight is still normal work, people sitting in the bathtub, bathtub drain pipe is at ground potential, wash bath faucets in its hands, at this time will be electric shock.

Equal potential connection is the metal body that all inside toilet (include conduit, pit, downpipe, metal towel rack to wait) link into an organic whole, connect with ground wire.

The electrical equipment inside toilet should have leakage protection, want to have reliable ground, make even equipotential connection.

Two last points need to be made in particular:

1. When single-phase electric shock occurs in human body (this kind of accident has the highest probability in the electric shock accident), that is, when a phase line (fire line) is contacted on the load side of the leakage protector, it can play a good protective role. If the body is insulated from the ground, the leakage protector cannot protect when a phase line and a zero line are touched.

2. Because the role of the leakage protector is to prevent it from happening, the importance of it cannot be reflected when the circuit works normally, and it is often not easy to attract people's attention. Some people in leakage protector action is not seriously looking for reasons, but leakage protector short or remove, this is extremely dangerous, is absolutely not allowed.

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