1. Lighting line failure caused by zero line disconnection
The voltage imbalance caused by the neutral wire breakage often causes damage to the appliance being used in one phase of the high voltage, and the ground voltage will appear at the break on the side of the neutral wire breakage load. In order to prevent the failure of the lighting line and the damage of the home appliance caused by the broken wire, the neutral wire should be the same cross-section wire as the phase wire, and should be connected reliably. Repeated grounding can also be performed at the incoming line and at the end of the line. In the event of a zero-line disconnection, the three-phase power supply can form a loop with the ground through repeated grounding devices to avoid accidents.
For the inspection of the neutral wire breakage fault, it is necessary to check whether the components such as the knife switch and the fuse are connected to the zero wire. If so, all the wires should be removed and the neutral wire should be directly and reliably connected. Check the connection point of the neutral line for disconnection, looseness, poor contact, and whether there is a situation where the neutral line is broken due to strong wind or other mechanical reasons.
2. Short circuit of lighting line
The short-circuit fault is manifested as: the fuse melts, and there is obvious burn marks and insulation carbonization in the short circuit, which will seriously burn the wire insulation layer and even cause fire. The common causes of short-circuit faults are as follows:
1) The installation does not meet the requirements. The strands of wire are not tightened, tinned, and the crimping is not tight and there are burrs.
2) The phase line and the neutral line are loosely connected, and the distance is too close. Some external forces are encountered, causing them to collide and cause a relative zero short circuit or a phase short circuit.
3) In bad weather, such as strong winds, the insulation support is damaged, the wires collide and rub against each other, the insulation of the wires is damaged, and a short circuit occurs; in rainy days, the waterproof facilities of electrical equipment are damaged, and the rainwater enters the electrical equipment and causes a short circuit.
4) There is a large amount of conductive dust in the environment where the electrical equipment is located. If the dustproof facilities are improperly selected or damaged, the conductive dust will fall into the electrical equipment, causing a short circuit failure.
5) Human factors, such as temporary movement of wires, switch boxes, switchboards, etc. during civil construction, improper handling, accidental collision with overhead lines during construction or digging of soil cables during excavation.
The short-circuit fault finding is generally a combination of branch road, segmentation and key part inspection, and the test light method is used for inspection.
3. Lighting line open circuit failure
After the lighting line breakage occurs, the load will not work properly. Common reasons for line breaks are as follows:
1) The load is too large to blow the fuse.
2) The switch contacts are loose and the contact is poor.
3) The crimping at the wire joint is not true, and the contact resistance is too large, causing local heat generation and causing oxidation at the joint. Especially when the copper-aluminum wire is connected, there is no transition joint causing severe corrosion at the joint.
4) Bad weather and human factors.
When looking for an open circuit fault, it can be tested with a test pencil, a multimeter, etc., and the segmentation search is combined with the key part inspection. For longer lines, the divisor method can be used to find the break point.
4. Lighting line leakage fault
Leakage of the lighting circuit is mainly caused by the insulation between the phase line and the neutral line being damaged by moisture or being polluted, resulting in leakage between the phase line and the neutral line; the insulation between the phase line and the neutral line is damaged by external force, and the phase is formed. Leakage between the line and the ground; the line runs for a long time, and the line insulation aging causes the line to leak. The method of checking for leakage is as follows.
1) Measure the value of the insulation resistance with an insulation resistance meter, or connect an ammeter to the main switch of the circuit under test. Turn off the power after disconnecting the load. If the pointer of the ammeter swings, it indicates that there is leakage and deflection. Big. Make sure to check for further leakage.
2) Cut the zero line. If the current meter indication is unchanged or the insulation resistance is constant, the leakage between the phase line and the earth is indicated. If the ammeter indicates zero return or the insulation resistance returns to normal, the leakage between the phase line and the neutral line is indicated. If the ammeter indication is small but not zero, or the insulation resistance is increased but still does not meet the requirements, it indicates that there is leakage between the phase line and the neutral line, the phase line and the earth.
3) Remove the shunt fuse or open the shunt switch. If the current meter indicates or the insulation resistance is unchanged, the total line leakage is indicated. If the current meter pointer returns to zero or the insulation resistance returns to normal, the shunt leakage is indicated; if the ammeter indication becomes smaller However, it is not zero, or the insulation resistance is increased but still does not meet the requirements, indicating that the main line and the sub-line have leakage. This will determine the extent of the leakage.
4) After determining the branch or line segment of the leakage according to the above method, then turn off the switch of the line lamp in turn. When the switch is disconnected, the ammeter indicates zero return or the insulation resistance is normal, indicating that the branch line is leaking. If the current meter indication becomes smaller or the insulation resistance increases, there is other leakage in addition to the leakage of this branch line; if all the lamps and switches are disconnected, the ammeter indication is unchanged or the insulation resistance is unchanged, indicating the section of the main line Leakage.
5) After the fault is narrowed down to a shorter line segment by the above method, it is possible to further check whether the joint of the section of the line, the junction box, the wire penetration wall, etc. have insulation damage and handle it.
5. Lighting circuit insulation resistance is reduced
The electrical lighting circuit has a long service life, the insulation is aging, the insulator is damaged, and the insulation of the wire is damp or worn, which will reduce the insulation resistance. The insulation resistance of the line should be checked regularly to detect problems and deal with them in a timely manner. The measurement method is as follows.
1) Measurement of insulation resistance between wires. First cut off the electrical equipment and then turn off the power. The insulation resistance meter shall be used to measure the insulation resistance between the wires. The relevant requirements shall be met. If the requirements are not met, further inspection shall be carried out.
2) Wire-to-ground insulation resistance measurement. Remove the power supply and disconnect the electrical equipment on the line. Connect one terminal on the insulation resistance meter to one of the wires to be tested. The other terminal of the insulation resistance meter is connected to the metal pipe of the water pipe and electrical equipment. Or a metal object such as a metal casing of a building that is in good contact with the earth, and then measured.
6. Fuse melt blown
1) The melt is blown for a short period of time. Due to the soft material of the melt, it is easy to be damaged during the installation process, and the melt itself may be uneven in thickness, and the resistance at the thinner portion is large. When the load is overloaded, it is first blown from here. The melt of the same specification should be replaced.
2) The melt is blasted so that the entire melt is melted. Generally due to short-circuit faults on the line, the cause of the fault should be identified and the melt replaced after removal.
3) The melt crimping screw loosens to cause an open circuit, and the crimping screw should be tightened when the melt is replaced.
7. The fuse and knife switch are overheated
1) The lacquer on the screw hole is melted and there are traces of runny.
2) The surface of the pure copper is formed with black copper oxide and is annealed and softened. The crimped screw cannot be loosened.
3) wires and knife switches, fuses, terminal crimping false; wire surface oxidation, poor contact; aluminum wire directly crimped on the copper terminals, since the electrochemical corrosion, aluminum wire corrosion, the contact resistance increases, Overheating occurs, causing an open circuit in severe cases.
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