Preventing electrical equipment (hereinafter referred to as electrical appliances) from being damaged by electricity, causing electric shock to people who come into contact with electrical appliances. One of the methods that can be used is to electrically connect the metal casing of the electrical appliance to the ground or the neutral line of the power system. Protect the ground or protect the zero. The author finds that many users, even some junior and intermediate electricians, are not clear about the selection of protective grounding and protection zero, the characteristics of protection zero and protective grounding, and the problems that should be paid attention to when protecting the zero. Some still have misunderstandings, resulting in There are a lot of safety hazards during construction and maintenance. In order to ensure the safety of electricity, the electrical equipment used in the grounding grid is protected against electric shock. The safety issues to be taken when protecting the zero is mentioned below.
First, the anti-electrical casing is charged with the advantage of protection and zero. The anti-electrical casing is charged. If the protective grounding is used, if the grounding resistance RG meets the requirement of not more than 4 ohms, if the electrical enclosure is equipped with a voltage of 220V, the grounding circuit is protected. Short-circuit current I=U/(R0+RG)=220/(4+4)=27.5(A), where R0 is the grounding resistance of the transformer neutral point called the working ground resistance. In order to ensure the reliable operation of the protection device, the grounding short-circuit current is not less than 1.25 times of the automatic switch setting current or 3 times of the fuse winding current. Therefore, the short-circuit current in the above formula can only guarantee that the breaking setting current does not exceed 27.5/1.25. That is, 22A automatic switch, or 27.5/3, that is, 9.2A fuse, if the rated current value of the protection device is greater than the above value, the protection device cannot operate quickly and reliably. At this time, the ground voltage will exist for a long time on the outer casing of the electrical equipment, which is very dangerous for the person who operates the electric appliance. When the protection is connected to zero, the short-circuit current when the insulation of the electrical enclosure is broken is much greater than 27.5(A). As long as the operating current of the protection device is properly selected, when the insulation breakdown causes a single-phase short circuit, the short-circuit current is usually large enough to make the protection device Quickly cut off the power to eliminate the risk of electric shock. It can be seen that in the grounding grid, in order to prevent the electrical equipment casing from being charged and injuring people, the protection grounding ratio is much better than the protection grounding effect.
Second, the protection of the grounding and protection of the choice of zero according to the provisions of China's "low-voltage user electrical installation regulations", electrical equipment powered by low-voltage public power grid or rural collective power grid should use protective grounding, not to use zero protection. This is because the utility grid and the rural collective power grid, the low-voltage line maintenance level is low, the power supply line is long, and the possibility of zero-line disconnection exists. If the protection is connected to zero, the zero-line disconnection, a power-consuming equipment casing With electricity, all the electrical equipment in this low-voltage system is live, which is very dangerous. Therefore, the procedure requires protective grounding.
Third, the protection and zero considerations
1. The neutral point of the power supply is well grounded, the zero line operation is reliable, and the protection is connected to zero. The working ground of the system must be reliable, that is, the neutral point of the power supply must have good grounding, and the grounding resistance should be below 4Ω. Except for the working zero line of the single-phase circuit, the fuses and switches cannot be installed on the zero line of the three-phase four-wire line. One is to prevent the phase voltage from causing electric shock when the neutral circuit is disconnected; the other is to prevent the phase voltage from being asymmetrical due to the unbalance of the three-phase load and damage the electrical equipment when the neutral circuit is disconnected.
2. The working zero line must be grounded repeatedly. In order to prevent the working neutral circuit from being disconnected, in addition to the good grounding of the neutral point, the working neutral line must be repeatedly grounded. According to the "Code for Design of Grounding for Industrial and Civil Power Devices" (GBJ65-83). In the power grid where the neutral point is directly grounded, the grounding of the trunk line and the branch line of the overhead line and the zero line of one kilometer along the line shall be repeatedly grounded. The grounding resistance of each repeated grounding device shall not exceed 10 ohms, and the working grounding resistance shall be 10 In the case of Europe, the grounding resistance of each repeated grounding device should not exceed 30 ohms, but the repeated grounding must not be less than 3. Otherwise, if the zero line breaks, in the zero-connecting device on the neutral circuit, as long as one of the outer casings is charged, the outer casing of all the devices exhibits a voltage equal to the phase voltage, which is very dangerous.
In addition, repeated grounding is an indispensable safety technical measure in the protection zero system. Its function has the following four points: one is to reduce the ground voltage of the leakage equipment; the other is to reduce the risk of zero trunk disconnection; the third is when the line, When the equipment is short-circuited to the ground, the grounding resistance is reduced in parallel with the working ground, the grounding resistance is reduced, the short-circuit current is increased, the operating speed of the protection device is accelerated, and the duration of the accident is shortened. Fourth, the shunting effect of the lightning current is repeated due to repeated grounding, and the overhead is improved. The lightning protection performance of the line is beneficial to limit the lightning overvoltage.
3. The zero line section shall not be less than one-half of the phase line section except for the single-phase load. In normal, there is no current or only a small unbalanced current in the neutral line, so the section may be smaller than the phase line. However, starting from the safety and reliability of the neutral line protection, in order to make the protection device operate quickly and reduce the zero-to-ground voltage when the fault occurs, the neutral line impedance should be as small as possible. For this reason, the zero line should have sufficient area. Generally, under the premise of meeting the single-phase load requirements of the line, the zero line section shall not be less than one-half of the phase line section. The electrical protection zero line shall also have sufficient mechanical strength. When using copper wire, it shall not be less than 1.5 square millimeter; when using aluminum wire, it shall not be less than 2.5 square millimeter; when bare wire is applied, it shall be increased to 4 square millimeter and 6 square respectively. Millimeter.
4. The protection of the equipment and the work of the neutral line should be reliable. The protection of the equipment is between the neutral line and the working zero line. The connection must be firm and ensure good contact. The protective neutral wire should be connected to the special grounding screw of the device; if necessary, spring washer or welding can be added. It is best not to use aluminum wire for the zero line. The connection between the protection zero line of the equipment and the working zero line should be connected to a place that is not susceptible to mechanical damage. The protective neutral of the equipment must be protected by the protective neutral when it is exposed to mechanical damage. At the same time, it is necessary to check the protection zero line frequently and find hidden dangers in time.
5. Single-phase load line protection zero line shall not borrow the working zero line when connecting the three-eye socket, it is not allowed to connect the hole of the power supply zero line of the socket to the hole of the protection zero line. Otherwise, if the zero line is loose or folded Will cause the metal casing of the equipment to be energized or to energize the enclosure when the neutral and cold wires are reversed. The correct connection of the three-eye socket is: connect the socket to the neutral line of the power supply, that is, the hole of the working zero line and the hole of the protection neutral line are connected to the common working zero line by two wires. That is, there is a line with a single-phase load, and the protection zero line must not borrow the working zero line. In addition, the protection neutrals of all electrical appliances must not be connected in series, but should be directly connected to the common working neutral.
6. In the same low-voltage power grid, it is not allowed to use protective grounding and protection to zero. In the same low-voltage power grid (referring to the same transformer or the same generator-powered grid), it is not allowed to use part of the electrical equipment for protective grounding, and the other part of the electrical equipment is used. Protected to zero. Otherwise, when the grounding device has a shell failure, the neutral line potential is raised, and the contact voltage can reach the value of the phase voltage, which increases the risk of electric shock.
7. The rated current of the protection equipment (fuse or circuit breaker) must be selected and adjusted according to safety requirements. The low-voltage power grid with protection and zero connection must be selected and set according to safety requirements. The protection of zero is essentially when a leakage occurs in the electrical equipment, the single-phase loop is formed by the neutral line, and the leakage current is increased to a short-circuit current, forcing the protection device on the line to act quickly to cut off the power. Therefore, the protection zero must have a reliable short circuit protection or an overcurrent protection device. Various protection devices must be selected and set according to safety requirements to improve the reliability of protection and zero connection. After the protection device is operated, it is necessary to find out the fault point and the cause of the fault. In particular, it should be noted whether the protection neutral line and its connection are damaged when the fault is short-circuited.
8. The use of protective equipment to protect against zeros is not a foolproof use of electrical equipment. It can only eliminate the serious fault of the electrical connection between the outer casing of the electrical appliance and the power supply. It cannot eliminate the leakage fault of the electrical enclosure, so the electrical enclosure is protected. At the same time of zero connection, other protective measures should be taken to eliminate the leakage fault of the electrical enclosure. The current common method is to install a current-type leakage protector.
9. Selecting the type of power distribution according to the power environment There are three types of low-voltage power distribution methods that use protection and zero connection, namely TN-S system, TN-C-S system and TN-C system. Among them, the TN-S system has a special protection zero line (PE line), that is, a system in which the protection zero line and the working zero line (N line) are completely separated, that is, the so-called three-phase five-wire power supply system, the explosion danger This type of system is used in places with high or high security requirements. With the development of the economy, residents in China's economically developed areas have begun to adopt this type of power supply. The TN-C-S system is a system in which the main line protection neutral line is shared with the front part of the working zero line (constituting the PEN line), and the rear part is separated. This system is commonly used in low-voltage incoming workshops and in civil buildings. The TN-S system is a system in which the main line protection zero line and the working zero line are completely shared. It is suitable for places with no explosion hazard and good safety. It is rarely used now.
100% authentic best 18650 cells, below is our regular inventory list:
authentic sony li ion battery cells
US18650VTC6 3000mAh 15A/20AdischargeUS18650VTC5A 2500mAh 30Adischarge
US18650VTC5 2500mAh 20Adischarge
US18650VTC4 2100mAh 30Adischarge
US18650V3 2200mAh 10Adischarge E bike cells
US18650VC7 3400mAh 5A/8Adischarge
US18650NC1 2900mAh 10Adischarge E bike cells
US454261A8T 1590mAhlipo cells
Original Sanyo cells:
NCR18650BF 3400mAh
NCR18650GA 3450mAh 10AdischargeE bike cells
UR16650ZTA 2500mAh
UR18650ZTA 4.35V 3000mAh
UR18650FJ 2100/2200mAh red top
UR18650FM 2500/2600mAh blue head
UR18650FK 2300/2400mAh green top
UR18650ZY 2450/2550mAh Made In Japan
UR18650ZY 2450/2550mAh
UR18650AY 2150/2250mAh white head
UR14500P 830mah
UR18500F(K) 1620/1700mAh
UR18650NSX 2600mAh 20Adischarge
UF103450PN 1880/2000mAh with fuse
UF103450PN 1880/2000mAh no fuse
UF463450F
UF703450 1430/1480mAh
UF653450 1250/1300mAh
UF624447F 1530mAh
UF553450ZP 1150/1200mAh
UF553450ZP 1150/1200mAh
UF553443ZU 1000mAh
UF463048F
UF553436G
Authentic Panasonic cells:
NCR18650B3 3400mAh
NCR18650A 3100mAh
NCR18650BM 3200mAh
NCR18650 2900mAh
NCR18650PF 2900mAh 10AdischargeE bike cells
NCA103450 2350mAh no breaker
NCA903864 3120mAh
NC-1900SCR
NCR18500A 1940/2040mAh
NCR18650GA 3450mAh 10AdischargeE bike cells
Original Samsung li ion cells:
INR18650-25RM 2500mAh 20Adischarge
INR18650-25RM 2500mAh 20Adischarge
INR18650-25R 2500mAh 20Adischarge,
INR18650-20RM 2000mAh 22Adischarge
INR18650-30Q 3000mAh 15Adischarge
ICR18650-30B 4.35V 3000mAh
INR18650-35E 3500mAh 10Adischarge
INR18650-29E 2900mAh 8.25Adischarge
INR18650-32E 3200mAh 10Adischarge
ICR18650-22P 2150mAh 10Adischarge
ICR18650-22PM 2150mAh 10Adischarge,
ICR18650-22F 2200mAh
ICR18650-22FM 2200mAh
ICR18650-26JM 2600mAh
ICR18650-26FM 2600mAh
ICR18650-26HM 2600mAh
Original LG cells:
INR18650HE4, 2500mAh 20Adischarge
INR18650F1L, 3400mAh
ICR18650S3, 2200mAh,
ICR18650B4/B4L, 2600mAh
ICR18650MF1/MF2,2200mAh,10Adischarge
ICR18650M26,2600mAh, 10Adischarge
INR18650MG1 2900mAh 10Adischarge
INR18650MH1 3200mAh 10Adischarge
INR18650MJ1 3500mAh 10Adischarger
18650 Battery,Best 18650 Battery,18650 Lithium Battery,18650 Lithium Ion Battery
Asarke Industry Co., Limited , https://www.asarke-industry.com