Low-voltage electrician operation permit examination questions and answers - Chinahourly

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When power is transmitted, the larger the general capacity, the longer the transmission distance, and the lower the transmission voltage should be safer.
The metal casing of the voltage transformer, the core and the end of the secondary side should be reliably grounded or connected to zero.
When the current transformer is in operation, the secondary circuit should be prevented from being short-circuited when the meter is exchanged.
High and low voltage disconnectors cannot be used to switch on and off the load current, but can be used to break the short circuit current.
When operating high and low voltage isolating switches, it must be well matched with the corresponding high and low voltage circuit breakers; when power is supplied, the isolation switch should be closed first, and then the circuit breaker should be closed; the operation sequence is the same when the power is off.
Under normal circumstances, when all power distribution stations are out of power, the switches of each load should be disconnected first, and then the switches of the capacitor bank should be disconnected.
The temperature of the upper layer of oil in the transformer tank should not exceed 55 ° C
The discharge circuit of the capacitor bank must be protected by a circuit breaker and a fuse.
A manual compensation method that increases the power factor is usually a capacitor with an appropriate capacity connected in series in an inductive load.
Shanghai area regulations: the entry point should not be small and 2.7M away from the land
Shanghai area regulations: The minimum cross-sectional area of ​​the entry line should be 4mm2.
Shanghai area regulations: the incoming line should be insulated with a good copper or aluminum core hard wire.
The power distribution room should have good ventilation and a reliable and reliable lighting system. The indoor lighting power switch should be located inside the power distribution room.
The secondary circuit of the current transformer should be equipped with a fuse for short circuit protection.
Shanghai area regulations: the central location of the billing energy meter should be 1.4-1.8M off the ground
The ratio of the rated current of the upper and lower fuses of the fuse shall be less than 2 times.
The insertion fuse should be installed vertically, and the rated current of the fuse should be not less than the rated current of the fuse.
The ambient temperature of the capacitor chamber must not exceed 35 °C.
The line device shall have sufficient insulation strength. The insulation strength of the indoor conductor and cable shall not be less than AC 450/750.
The maximum current allowed by wires and cables depends on the material and structure and the mode of operation, in addition to the cross-sectional area.
When selecting the cross-sectional area of ​​the conductor, it must also meet the branching requirements of the line. On the distribution branch line, each single-phase shunt should be illuminated, and the number of attached lamps should not exceed 15.
Building outline lighting should not exceed 50 single-phase shunt lamps.
On the distribution branch line, the maximum load current of each branch of the electric heating should not exceed 25A.
In the main circuit of the gas discharge lamp, the N-line cross section should not be larger than the phase line cross section.
When the plastic sheathed wire is laid, the minimum cross-sectional area of ​​the copper core is 1.5mm2, which is connected by a head tap or in a junction box.
When the sheathed wire is in close contact with the grounding conductor and the non-heating pipe, the steel pipe shall be protected, and the place susceptible to mechanical damage shall be insulated.
The rated voltage of the pipe-through conductor shall not be lower than that of the AC 400v. There shall be no joints in the pipe.
The minimum cross-section of the tube-wound wire, the copper-core insulated wire should not be smaller than 1mm2, and the aluminum-core insulated wire should not be smaller than 1.5mm2.
The steel pipe or the two ends of the steel pipe are connected with round steel or flat steel to make a good electrical path. The resistance value at any two points should be no more than the radius of curvature of the 4 ohm wire diameter, which should be no less than the wire tube. 6 times the diameter.
The bending angle of the steel pipe should not be greater than 90°, and the diameter of the pipe should not be bent and reduced.
The buried depth of the laying cable is not more than 0.7m
In a metal trunking, control, signal or similar line, the total cross-section of the wire or cable shall not exceed 40 截面 of the cross-section in the trunking, and the number of wires and cables shall not be limited.
The two ends of the joint in the metal wire trough should be connected by green/yellow two-color soft wire. The wire trough should be grounded or connected to zero reliably, and can also serve as the grounding conductor of the equipment.
When the temporary line is erected, it should be connected to one end of the power supply and then to one end of the power equipment. When the line is removed, the order is reversed.
Electrical equipment such as switches, latches, fuses and leakage protectors that are temporarily installed in electrical power shall be installed in the switch box.
Separate local illumination must be used in crowded locations.
Chandeliers weighing more than 1KG must be supported by metal chains or other methods to force the chandelier wires.
Fluorescent lamps should not be placed close to the flat surface of flammable buildings, close to the flat-top fluorescent lamps, and the ballast in the lamp holder should be sealed.
The iodine-tungsten lamp should be installed horizontally, and the inclination should not exceed 10°, otherwise the service life of the lamp will be shortened.
When moving the daily electrical appliance, the electrical switch must be disconnected.
Generally, all Class I tools should be used in the workplace. If Class II tools are used, a leakage protector or isolation transformer is required.
Class II tools should be used in narrow locations such as boilers, metal containers, and pipes.
In the grounding or zeroing system, when the protective conductor is made of insulated copper core wire, its cross section should not be smaller than 1,5mm2
The lightning protection device consists of a lightning receptor, a down conductor and a grounding wire.
The protection radius of the lightning rod on the ground is 0, 5 times the height of the lightning rod.
The lightning rod is attached to the building or structure to allow the grounding resistance to be grounded to the electrical equipment, but the grounding resistance of the common grounding device is not more than 4 ohms.
The lightning arrester is the main measure to prevent lightning wave intrusion. The installation is as close as possible to the object to be protected. The grounding resistance of the independent grounding device should not be as large as that of all 4 ohm mobile electrical equipment and hand-held power tools.
In order to avoid malfunction, the non-operating current of the leakage protector is lower than 1/2 of the operating current.
Wires and cables generate heat when passing current, but generate heat when passing normal normal load current, not less than the maximum allowable temperature during normal operation.
In a three-phase four-wire or two-phase three-wire distribution line, when the electrical load is mostly single-phase electrical equipment, the cross section of the N-line or PEN line is not easily larger than the phase-line cross section.
The steel pipe wiring has the advantages of moisture proof, fireproof, corrosion resistance, etc., and can be used in places where the metal has serious corrosion.
All wires of an AC circuit shall be worn in the same steel pipe. Plastic pipes are not allowed to pass through a single wire, except DC circuits and protective earthing wires.
Semi-rigid plastic pipes can only be used in general houses of six floors and below. The minimum pipe diameter should not be less than the inner diameter of 10mm.
The AC single-core cable must not be worn in the steel pipe, but the single-core cable of the same circuit can be put into the same steel pipe together.
The connection of the metal trunking should be continuous and uninterrupted, and the connecting bolts should be fixed from the outside to the inside and the anti-loose device.
The low-voltage circuit breaker is a kind of protection device widely used in low-voltage distribution lines, and can also be used as a control switch for frequently starting the motor.
When installing the open load switch, it should be installed vertically, so that the switch operation direction is from the bottom to the top, and the switch is closed from the top to the bottom to prevent mis-closing.
In the same power supply system, the power equipment should be protected from zero, and the lighting and sockets can be grounded.
The ammeter should be connected in parallel with the load circuit under test. The voltmeter should be connected in series with the load circuit under test.
When the insulation resistance meter measures the insulation resistance of electrical equipment, it should be read after stopping the shaking.
The multimeter can measure the AC voltage, DC voltage, current and resistance of the electrical equipment under the charged state.
If the brain cells are hypoxic for more than 4 to 6 minutes, irreversible damage can occur, so if someone finds "clinical death", they must immediately perform mouth-to-mouth resuscitation.
When "clinical death" occurs during electric shock, the tissue cells in the body are severely deprived of oxygen, which is very urgent. Time is life and must be sent to the hospital immediately.
When the heart is pressed in vitro, the palm of the hand should be placed in the nip, and the correct part of the nip is the left chest outcrop.
An electrician who does not have a special operation permit can only perform maintenance work on all electrical equipment or lines that have been cut off.

The power outage maintenance work must be carried out after the test is clear and there is no electricity. If it is not possible to determine whether the power is cut off, the insulation protection should be done before the maintenance can be carried out.
Work on a live line, such as disconnecting the wire, first disconnect the phase line, then disconnect the neutral line. When lapping the wire, connect the phase line first, followed by the neutral line.
When using an insulated rod for live operation, do not wear insulated gloves.
The live working must be monitored by a person with practical experience in live working, and the guardian can operate directly if necessary.
The portable grounding wire must be installed after it has been verified that there is no electricity. When connecting, it should be connected to the grounding terminal first, then connected to the equipment or the line terminal. The order of removal is the same.
The portable grounding wire shall be a multi-strand copper core hard wire with a cross-section of not less than 25mm2 and a transparent insulating material.
All screen guards must be protected against grounding or zeroing to prevent accidental electrification of the screen protector and cause electric shock.
The insulating material, also called dielectric, is a material having a resistivity of 10/5 ohm·m or more.
An extra low voltage power outlet is provided, and in special cases, it can also be plugged into the plug of a non-extra low voltage consumer.
The input circuit and the output circuit that provide extra low voltage must be isolated on the circuit, so they must be taken from the autotransformer.
For a long period of overload operation, the intercepting portion of the electric equipment will be excessively heated, so that the insulation performance of the electric equipment is improved.
Generally, an overload protection device should be installed on the continuously running motor, and the position is easy to move away from the control device or component.
<<The People's Republic of China Safety Production Law>> was implemented on October 1, 2002.
Practitioners can get on the job by knowing the safety production regulations and operating procedures in their workplaces and jobs.
Specialized safety production laws include <<Fire Law>>, <<Occupational Disease Prevention and Control Law>>, <<Dangerous Chemical Safety Management Regulations>>, etc.
Electrical workers who have obtained intermediate or above skills certificates, or electrical workers with intermediate titles or above, can work on the job.