1. Regulations for Wiring Single-Phase Power Outlets
There are various types of single-phase outlets, commonly divided into two-hole and three-hole types.
Two holes are arranged side by side, while three holes form a “T” shape.
Next to the wiring holes are marked letters: L for live, N for neutral, and E in the center of the three holes indicates ground.
When facing the outlet, there are regulations for connecting each hole.
Connect the neutral wire to the left, the live wire to the right, and the ground wire to the center.
2. Selecting Residual Current Devices (RCD)
When selecting an RCD, the power supply method is the first consideration.
For single-phase power at 220V, use two wires for two-level or single-level.
For three-phase three-wire at 380V, choose a three-level RCD.
For three-phase four-wire at 380V, use either three-level or four-level.
“Level” indicates the number of switch contacts, while “wire” indicates the incoming and outgoing lines.
3. Troubleshooting Non-Lighting Bulbs
When a bulb doesn’t light, it can be frustrating. A common reason is a broken filament.
If it’s a transparent bulb, you can see it; otherwise, use a voltage tester.
When the switch is on, if both ends do not light, the live wire is broken. If one lights and one goes out, the filament is broken; if both light, the neutral wire is broken.
4. Checking for Broken Cores Before Burying Underground Wires
Before burying underground wires, check for broken cores using a megohmmeter; connect one end to the wire.
Submerge the other end in water, and connect the E terminal of the instrument accordingly.
Slowly shake the megohmmeter; if the needle does not reach zero, there is a broken line.
To find the break point, use instrument DG3.
For single-phase AC, connect one end, and attach the instrument to the buried wire.
Move slowly from one end to the other; if the indicator light is on, the line is intact.
If the instrument light goes out, that point is where the line is broken.
5. Using a Low-Voltage Voltage Tester to Diagnose AC Single-Phase Circuit Faults
For AC voltage testing, if the tester lights up, it’s a live wire; if not, it’s ground.
For circuit faults, you can check the live and ground while powered on.
If everything is normal, check the devices; if the circuit is disconnected, it’s not suspicious.
If neither end lights up, the live wire is disconnected.
If both ends light up, the neutral wire is broken or disconnected.
6. Measuring DC Voltage with a Pointer Multimeter
Before measuring, first zero the meter and choose an appropriate range.
Identify the positive and negative terminals of the circuit, and connect the wires correctly.
Connect the black probe to the negative terminal and the red probe to the positive terminal.
If the needle moves in reverse, the connections are reversed.
7. Measuring DC Current with a Pointer Multimeter
Before measuring, first zero the meter and choose an appropriate range.
Identify the positive and negative terminals of the circuit, and connect in series correctly.
Connect the black probe to the negative terminal and the red probe to the positive terminal.
If the needle moves in reverse, the connections are reversed.
8. Measuring DC Resistance of Conductors with a Pointer Multimeter
Select the resistance range before measuring, and zero the meter after selecting.
Short the two probes to see the needle; if it’s not at zero, adjust it.
Rotate the ohms zero knob until the needle reads zero.
If the knob is at the end and there is still a reading, replace the battery and adjust again.
Ensure good contact; if the resistance is high, keep your hands off to ensure accurate readings, ideally with the needle within the grid.
After measuring, turn off the power and set the knob back to voltage.
9. Judging the Condition of a Capacitor with a Pointer Multimeter
To roughly judge a capacitor’s condition, a multimeter can be used.
Set the resistance to the K range, and connect the probes to each terminal.
The needle should swing close to zero, then slowly return to a certain point and stop; the more it returns, the healthier it is.
If it stays at zero, there is a short circuit; if it returns less, there is leakage. If the meter does not move, the internal circuit of the capacitor is broken.
10. Using Charge and Discharge Method to Judge Capacitor Condition
To roughly judge a capacitor’s condition, the charge and discharge method can be used.
Connect a DC voltage across the capacitor for a short time, then cut off.
Touch the two terminals with a conductor and watch for sparks.
If there is a spark, it’s good; if not, it’s bad. A larger spark indicates a better condition.
11. Estimating Rated Current for a Known Three-Phase Asynchronous Motor
For small to medium capacity high and low voltage, estimate the current based on kilowatts.
The relationship is given as a median; if the capacity is large, reduce it; if small, increase it.
One kilowatt equals two amperes, commonly for low voltage at 380V.
High voltage motors at 3000V, four kilowatts equals one amp; for higher voltage at 6000V, eight kilowatts equals one amp; rated voltage at 10000V, thirteen kilowatts equals one amp.
12. Wiring Method for Converting a Three-Phase 380V Motor to Single-Phase 220V Power Supply
For a three-phase motor converted to single-phase, connect the windings as originally.
All three terminals are useful; two connect to the power supply, one connects to the capacitor.
After connecting the capacitor, connect the power supply to the neutral and live wires to reverse the motor direction.
For three-phase to single-phase conversion, and connect the capacitor’s capacity.
Working capacitance depends on the connection; star connection is smaller, delta connection is larger.
For a hundred-watt motor, use microfarads; for delta connection, ten microfarads, for star connection, six.
Starting capacitance can be the same; for ten watts, two to three microfarads.
Capacitance voltage rating depends on the power supply: 220V power supply is 330V.
13. Phase Relationship Between Current and Voltage in Inductive Load Circuits
Inductance is clever in its “induction”; emotions require time to come and go.
When first meeting, it’s strange; it’s hard to express what’s in the heart.
Once separation is needed, “the lotus root is broken yet the silk is still connected”; there’s still longing.
When the power is on, the voltage rises, but the current takes time to reach.
When the power is cut, the voltage drops, but the current takes time to cut off.
This analogy is simple: voltage leads current; the two differ by an angle, with a maximum value of ninety degrees.
14. Estimating the Weight of Wires per Kilometer
The weight of wire per kilometer depends on its cross-section and type.
The cross-sectional area is in square millimeters, multiplied by different coefficients.
Hard aluminum is the lightest at 2.8, pure aluminum is next at three.
Steel-core aluminum strands are multiplied by four, while iron is heavier at 7.8; pure copper is 8.8, and steel strands are the heaviest at 9.0.
Consider sag and binding, then multiply by 1.03. The relevant formula is: mass = density × volume.
Volume = base area × height.
15. Principles of Generators and the Right-Hand Rule
Wires cutting through magnetic lines induce electromagnetic force.
When the wire connects to a closed circuit, current flows through it.
To determine the direction of flow, use the right hand; extend your right hand to form a plane.
Move the thumb in the direction of motion; the palm faces the N pole, and the four fingers indicate the current direction, also indicating the positive terminal.
16. Kirchhoff’s First and Second Laws
Kirchhoff is a famous figure; he invented circuit laws.
The first law states that the current at a junction is equal to the sum of currents flowing in and out.
The second law states that the voltage around a closed loop is equal to the sum of voltage drops and potentials.
17. Relationship Between Rectifier Power Output DC Voltage and Input AC Voltage, and Reverse Voltage of Rectifier Diodes
AC voltage is converted to DC; how to determine the output voltage?
The input voltage is 100; for single-phase half-wave, it’s 45.
For three-phase half-wave, it’s 117; half-wave is twice the full-wave. If using thyristors, start from zero to the peak.
Remember the reverse voltage for the diode: single-phase and three-phase have different values; for single-phase bridge, it’s 141, and for three-phase bridge, it’s 239.
Note: The input voltage should be the phase voltage.
18. Calculating Total Resistance of Resistors in Series and Parallel
Resistance in series increases; the longer the series, the greater the resistance.
Resistance in parallel decreases; it’s equivalent to an increasing cross-section.
Total resistance in parallel is harder to calculate; first, find the reciprocals of each value.
The reciprocal of the sum of reciprocals is the total resistance. For only two resistors in parallel, the total resistance can be simply calculated as the product of the two resistors as the numerator and their sum as the denominator.
19. Two Wiring Methods and Two Output Methods for Three-Phase AC Power Supply
There are two wiring methods for three-phase: one is delta, and the other is star.
Delta connection forms a triangle with three vertices for three-phase lines.
Star connection has three tails connected at one point, called the neutral point.
Three heads lead out the three-phase lines, with the midpoint as the neutral line.
The phase line is commonly called the live line, and the neutral line is called the zero line.
Star connection can produce two types of lines: three-phase three-wire and four-wire.
Three-phase three-wire has no neutral line, while three-phase four-wire has a neutral line.
20. Methods for Determining the Polarity of Rectifier Diodes
Diodes have two terminals: anode and cathode.
Determining polarity is simple; first, refer to the diagram: the triangle end is the cathode, and the short bar end is the anode.
If there’s no diagram, check the shape; the rounded end is the anode.
Larger specifications with screws have the screw end as the anode.
If unsure, use a meter to measure: prepare a multimeter set to the 100 ohm resistance range; connect the probes to the terminals in both polarities and compare the resistance values. One will be larger than the other; note carefully.
If the resistance is low, check the probes: red for the anode, black for the cathode.
21. Connection Methods for Bridge Rectifier Circuits and Protection with Resistors and Capacitors
Single-phase bridge uses four diodes; pair them in series and then connect in parallel.
Parallel connection outputs DC, with two diodes connecting to the power supply.
Three-phase bridge uses six diodes; pair them in series and then connect in parallel.
Parallel connection outputs DC, with two diodes connecting to the power supply.
For diode protection, there are three connection methods to choose from:
One connects on the AC side, another on the DC side, and a more complex one connects across each diode for inductive load back EMF, with parallel diodes for sustained protection.
22. Properties of Magnets, Magnetic Fields, and Magnetic Field Lines
No matter the size or thickness, magnets always have two poles.
The south pole is S, and the north pole is N; like poles repel, and opposite poles attract, which is a universal principle.
Magnetic fields and magnetic field lines describe that each line is a closed loop.
Outside, the lines go from N to S, and inside, from S to N.
The lines do not cross each other and are relatively dense at both ends.
23. Filter Circuits to Reduce Output Current Ripple
To achieve stable current, filter circuits are connected at the output.
One capacitor and one inductor form a T-shaped circuit.
Two capacitors and one inductor are called a Pi circuit, while a simpler one consists of two capacitors and one resistor.
24. Effects of Brush Deviation from the Neutral Line and Adjustment Methods
After energizing the excitation, observe the instrument.
If the instrument needle swings back and forth, with a large swing, the brush is misaligned.
Gently rotate the brush holder until the swing is minimized.
When the motor is powered on, compare the speeds in both directions.
If the difference is significant, it indicates that the brush is misaligned.
Gently rotate the brush holder until the difference is minimized.
25. Effects of Brush Deviation from the Neutral Line and Adjustment Methods
After energizing the excitation, observe the instrument.
If the instrument needle swings back and forth, with a large swing, the brush is misaligned.
Gently rotate the brush holder until the swing is minimized.
When the motor is powered on, compare the speeds in both directions.
If the difference is significant, it indicates that the brush is misaligned.
Gently rotate the brush holder until the difference is minimized.
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