24 mnemonic rules for electricians

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1. Regulations for wiring single-phase power sockets: There are various types of single-phase sockets, which are usually divided into two-hole and three-hole types. Two holes are arranged side by side on the left and right, while three holes form a triangular pattern. Letters are marked next to the wiring holes: L for live and N for neutral. Among the three holes, there is also an E, indicating that the ground connection is in the middle. When orienting the socket, there are specified rules for connecting wires to each hole. Connect the neutral wire to the left and the live wire to the right; connect the protective ground wire to the center. 2. Selection of residual current devices: When selecting residual current devices, the power supply method takes precedence. Single-phase power supply, 220 volts, two-wire two-stage or single-stage. For a three-phase three-wire 380V system, choose a three-stage protector. Three-phase four-wire: 380 volts; four-wire systems: three or four levels. ““Level” indicates the switch contacts; “Line” refers to the incoming and outgoing wires. 3. Methods for determining why a bulb doesn’t light up: A non-functional bulb can be quite frustrating; the most common cause is a broken filament. Transparent bulbs can be seen; otherwise, a test pen can be used for verification. When the switch is closed, neither end lights up, indicating that the live wire is broken. The filament breaks when the light flickers on and off; the neutral wire is broken if both ends are lit. 4. Methods for checking for broken cores and identifying break points in buried wires before installation: Before burying the wires, it is necessary to check each wire for any broken cores. Check using a megohmmeter: connect one end of the wire to terminal L, submerge the other end of the wire in water, and do the same for terminal E of the meter. Slowly rotate the megohmmeter; if the needle does not reach zero, there is a broken connection. To locate where the break in the wire is, use the DG3 instrument. Connect one end of the single-phase AC power supply to the instrument; then attach the instrument to the buried wire. Slowly move it along the length of the wire. If the instrument’s light remains on, the wire is intact. However, if the light goes out, that point is where the wire is broken. 5. Method of using a low-voltage test pen to diagnose faults in single-phase AC circuits: For testing AC circuits, if the test pen lights up, it indicates that it’s the live wire; if it doesn’t light up, it’s the neutral wire. Circuit faults can be checked by measuring live and ground with power applied. The on/off status is normal; the device checks out fine. No suspicion of any circuit disconnection. If neither end is lit, the live wire of the power supply has been disconnected. If both ends are bright, the neutral wire is broken or disconnected. 6. Method of measuring DC voltage with a pointer multimeter: Zero the instrument before measurement, and select an appropriate range. Determine the positive and negative poles of the circuit, and be clear about the parallel wiring. The black test lead should be connected to the negative pole, while the red test lead should be connected to the positive pole. If the hands of the gauge rotate in the opposite direction, the positive and negative poles of the wiring are reversed. 7. Method of measuring DC current using an analog multimeter: Zero the meter before measurement, and select an appropriate range. Determine the positive and negative poles of the circuit, and be clear about the series wiring. The black test lead should be connected to the negative pole, while the red test lead should be connected to the positive pole. If the hands of the gauge rotate in the opposite direction, the positive and negative poles of the wiring are reversed. 8. Method of measuring the DC resistance of a conductor using an analog multimeter: Select the appropriate range for measuring resistance, and then zero the instrument after selecting that range. For two short circuits, check the gauge needles; if they are not at zero, make adjustments. Rotate the ohm zero adjustment knob until the pointer reaches zero. There are still a few numbers at the end of the knob; replace the battery and then readjust it. The contact must be good; both hands should be suspended in the air when there is high resistance. To ensure accurate measurement values, it’s best for the pointer to stay within the marks. After the measurement is complete, turn off the power and adjust the knob to the voltage setting. 9. Using a pointer multimeter to determine the quality of a capacitor – A multimeter can be used for a rough assessment of whether a capacitor is in good condition or not. Use the resistance times K setting, with each test lead connected to one terminal. The hand swings close to zero, then slowly moves back. Stop when you reach a certain place; the more you return, the healthier it is. There is a short circuit when it reaches zero, while there is less leakage current when it returns. The meter stops working when measurement begins; there is a break in the internal circuit of the capacitor. 10. Using charging and discharging methods to determine the quality of capacitors – For a rough assessment of whether a capacitor is good or not, the charging and discharging method can be used. Direct current is applied across the capacitor, and it is disconnected after a short while. The conductor point is connected to two poles; pay attention to whether there is any spark. The presence of a spark is good while its absence is bad, and a larger spark indicates a stronger signal. 11. Given the rated capacity and voltage of a three-phase asynchronous motor, determine an approximate value for the rated current. For motors of medium and small capacities, regardless of voltage level, the current can be estimated based on the kilowatt rating. The relationship is that the median is used, with larger values decreasing and smaller values increasing. One kilowatt, two amperes; commonly 380 volts at low voltage. The high-voltage motor has a voltage of 3,000 volts, and its power is four kilowatts with a current of one ampere. The voltage is higher at six thousand volts, with a current of eight kilowatts per ampere. The rated voltage goes up to 10,000 volts; 13 kilowatts correspond to 1 ampere. 12. Wiring method when converting a three-phase 380V motor to operate on a single-phase 220V power supply, and calculation of the capacitance value of the capacitor to be used. When changing from three phases to single phase, the winding connection remains unchanged. All three terminals are useful: two are for connecting to the power supply, and one is for connecting a capacitor. After connection, connect to the power supply; the order of connecting neutral and live wires is reversed. Changing a three-phase motor to single-phase and the capacity of the connected capacitor. The working capacitance depends on the connection method: star connection results in a smaller value, while delta connection yields a larger value. For 100-watt motors, the microfarad value is ten for delta connection and six for star connection. The starting capacitor can be of the same size, 10 watts, 2 to 3 microfarads. The voltage rating of capacitors depends on the power supply; for a 220V supply, it’s 330V. 13. The phase relationship between current and voltage in a resistive load circuit. The beauty of an inductor lies in its ability to \"sense\" – it takes time for emotions to arise and fade away. At first meeting, we felt very strange to each other, and it was hard to express our thoughts. Once it’s time to part, there remains lingering affection despite the separation. When power is supplied, voltage is applied, but current takes some time to flow. When the power supply voltage is cut off, it is difficult to stop the current immediately. The above analogy is quite easy to understand: voltage comes first, and current follows. The difference between the two is an electrical angle, with a maximum value of ninety degrees. 14. Estimation of the weight per kilometer of wire: The weight of wire per kilometer depends on its cross-sectional area and type; the cross-sectional area is expressed in square millimeters, and different coefficient values are used for calculation. Duralumin is the lightest at 2.8, followed by pure aluminum at around 3.0. Aluminum conductor with steel core multiplied by four; 7.8 iron is relatively heavy. Pure copper weighs 8.8 again, while steel strands weigh the most at 9.0. Consider the sag and binding, then multiply by 1.03. 　15. Principle of generators and the right-hand rule: A wire cuts through magnetic field lines, inducing an electromotive force. When a wire is connected to a closed circuit, current flows through it. To determine the direction of flow, use your right hand; extend it flat. The wire moves toward the thumb, with the palm facing the N pole. The four-finger direction indicates the current flow, and this end is also the positive terminal. 16. Kirchhoff’s first and second laws. Kirchhoff is a famous figure; he invented the laws of circuits. The node current is first, with equal outflow and inflow in the two phases. The loop voltage is the second one; the voltage drop and potential are equal. 17. The relationship between the DC voltage output by a rectifier power supply and the AC voltage input, as well as the reverse voltage of the rectifying diodes. How is the output voltage determined when converting AC voltage to DC? The input voltage is one hundred, and for single-phase half-wave it is four five. Three-phase half-wave: 117; twice the number of half-waves equals the number of full-waves. If thyristors are used, it goes from zero to the maximum value. Remember regarding the tube backpressure: the numbers differ for single-phase and three-phase systems. Single-phase bridge: 141; Three-phase bridge: 239. 18. Calculation of the total resistance when resistors are connected in series and parallel. The resistance increases as resistors are connected in series; the longer the series connection, the greater the resistance. The parallel resistance value decreases, and the equivalent cross-sectional area increases. It is difficult to determine the total parallel resistance; first, the reciprocals of each value must be found. The reciprocal of the sum of the reciprocals is the resistance when connected in parallel. In parallel, there are only two resistors, so the total resistance can be calculated using a simplified formula. The product of the two resistances is used as the numerator, and the sum of the two resistances is used as the denominator. 19. Two wiring methods and two outlet configurations for three-phase AC power supplies. There are two types of three-phase wiring: delta and star. The corners form a triangle, with the three phase wires at the three vertices. Stars are connected to three tails with a single point in between; this connecting point is called the neutral point. Three conductors lead to the three phase wires; the neutral wire comes from the midpoint. The phase wire is commonly known as the live wire, while the neutral wire is commonly known as the neutral line. In a star connection, two types of wiring can be produced: three-phase three-wire and four-wire. Three-phase three-wire systems have no neutral wire, while three-phase four-wire systems have a neutral wire. 20. Method for determining the positive and negative poles of a rectifier diode: A diode has two poles, an anode and a cathode. Determining polarity is simple; first, one can refer to the chart. One end of the triangle is highly negative, while the end with the short bar is the anode. Without a diagram to show the shape, the end that is rounder is the anode. Larger sizes come with screws, one end of which is anode. If you’re not confident using a meter, have a multimeter ready. Multiply by the 100 ohm resistance setting, with the two probes connected to the electrodes respectively. Measure the resistance values twice, forward and reverse; note carefully which one is higher and which one is lower. When the resistance is low, check the test leads: red indicates the positive electrode and black the negative one. 21. Connection method of bridge rectifier circuits, as well as issues related to resistance and capacitance protection and rectifier diodes: In a single-phase bridge rectifier, there are four diodes, which are connected in pairs in series and then combined in parallel. DC is output at both ends in parallel, and the connection point of the two tubes leads to the power supply. Six tubes in a three-phase bridge configuration, connected in pairs in series and then in parallel. DC is output at both ends in parallel, and the connection point of the two tubes leads to the power supply. RC protection diode – three connection methods to choose from. One is connected to the AC side, and the other is connected to the DC side. There is also a more complex type, with one at each end of the tube. Reverse voltage of inductive load, with a parallel continuous diode. 22. Magnets and their properties, magnetic fields, and magnetic field lines: Regardless of their size or thickness, magnets have two poles. South Pole S, North Pole N – the maximum magnetic force at each end. Like poles repel, opposite poles attract; this principle applies to everything. Describe the magnetic field lines, each of which is a closed curve. From N to S outside the body, and from S to N inside the body. The lines do not intersect with each other and are relatively dense at both ends. 23. The filtering circuit designed to reduce output current ripple: To obtain a stable current, the filtering circuit is connected to the output. One capacitor and one resistor, connected to form a T-shaped circuit. Two capacitors and one inductor; this configuration is called a Pi circuit. There is also a simpler version, with two capacitors and one resistor. 24. Effects of the brush deviating from the neutral line and methods for adjustment: Turn on and then turn off the excitation, while monitoring the instruments. The instrument pointer swings back and forth; a large amplitude of swinging causes the brushes to shift. Gently rotate the brush holder to adjust the amplitude to the minimum. The motor is powered on to rotate in both directions, and the two speeds are subtracted from each other. If the resulting difference is large, it indicates that the brush is offset. Gently rotate the brush holder to fine-tune the minimum difference.