October 20, 2023

Practical formulas for beginners, 20 essential basic knowledge for electricians

As a beginner electrician, you may have been confused and hesitant. The knowledge related to electrical is so broad that one feels there is no way to get started. As a type of work that is very oriented towards level of technical knowledge and experience, electricians must remember basic knowledge of electricians and skillfully use it due to their specificity.

Today I would like to share with you some basic electrical knowledge. If you want to become a good electrician, this basic knowledge is essential.

Practical formulas for beginners, 20 essential basic knowledge for electricians

1. Rules for connecting electrical outlets

There are many types of single-phase sockets, usually divided into two and three holes. Two holes are divided into left and right sides next to each other, and three holes form a character figure. The letters marked next to wiring hole are L for fire and N for zero. The three holes also have an E, which means ground is in middle. Facing outlet, and wiring of each hole has rules. The left one is connected to zero line, right one is connected to fire line, and protection ground is connected to center.

2. Leak Protection Device Selection

Select a leakage protection device and a power supply method. Two hundred and two single-phase power supplies, two-wire two-stage or single-stage. Three-phase three-wire three hundred and eighty, select three-level protection. Three-phase four-wire three hundred and eight, four-wire three- or four-wire. "Level" means switch contact. "Line" means incoming and outgoing wires

3. Inspection of a break in core and determination of break point before burying underground conductors

Before burying underground wire, check for a broken core. Use a megger to check, connect wire to one end L, put wire into water at other end, do same to end E of meter, slowly shake megger, if arrow is less than zero, it means wire is broken. Find breakpoint, use DG3 fixture, connect one end of single-phase AC, touch fixture to ground and insert wire, move slowly from beginning to end, fixture's light is not interrupted. , if instrument indicator is off, this is a breakpoint.

4. Low-Voltage Electroscope for Single-Phase AC Fault Detection

Use an electric pen to check AC electrical performance when live wire indicator is on and ground is off. Circuit faults can be checked, power on, and fire and ground measured. Lights up and turns off Check equipment is normal, open circuit does not cause suspicion. If both ends are off, live power wire has been disconnected. If both ends are lit, neutral wire is broken or disconnected.

5. Measure DC voltage with a dial multimeter

Before measuring, set to zero and select a moderate range. Determine positive and negative poles of circuit and make sure parallel wiring is clear. Connect black test lead to negative pole and red test lead to positive electrode. If clock hands rotate in opposite direction, positive and negative polarities of wiring are reversed.

6. Pointer multimeter for measuring direct current

Before measuring, set to zero and select a moderate range. Identify positive and negativee poles of circuit, series connection must be clear. Connect black test lead to negative pole and red test lead to positive electrode. If clock hands rotate in opposite direction, positive and negative polarities of wiring are reversed.

7. Measure resistance of DC conductors with a dial multimeter

Select resistance measurement range and set it to zero after selecting range. Check arrows for two short circuits, if not zero, then you need to adjust. Rotate resistance zero button until clock hands reach zero. There is still a number on knob at end, replace battery and adjust again. The contact must be good and blocking hands must be suspended. The measurement value must be accurate and clock hands must be in grid. After measuring, turn off power and turn knob to voltage.

8. Multimeter to determine if a capacitor is good or bad

Roughly judge whether a good capacitor or a bad one, multimeter will withstand. Use resistance to multiply K-file and connect probes to one end. The arrows swing almost to zero, then slowly return. Find a place to stop and more you come back healthier you will be. A short circuit occurs when there is no movement to zero, and on return, leakage is less. The counter does not run at beginning of measurement, and internal circuit of capacitor is broken.

9. Use charge and discharge method to determine if a capacitor is good or bad

Roughly estimate whether a capacitor is good or bad, charging and discharging method can withstand it. The two ends of capacitor are connected to DC and after a while it will turn off. Connect wires to two poles and watch for sparks. If there is fire, then it is good, and if there is no fire, then it is bad. The same fire is bigger and fuller.

10. Phase relationship between current and voltage in an inductive load circuit

The beauty of inductance lies in word "feeling". It takes time for feelings to come and go. It was very strange when we first met, and it was hard to tell what was on my mind. Since it is necessary to part, "the root is broken" and still yearns for love. After turning on power and increasing voltage, it is difficult to reach current for a while. Turn off supply voltage, and current is difficult to turn off for a while. The above analogy is popular and tension flows from front and then from back. There is an electrical angle difference between them, and maximum value is 90 degrees.

11. Estimate wire weight per kilometer

The weight of a kilometer of wire depends on section and type, unit of section is mm square, and value of multiplied coefficient is different. The lightest duralumin is 2.8, followed by pure aluminum. An aluminum strand with a steel core is multiplied by four, and an iron withseven points eight is heavier. The weight of pure copper is 8.8, weight of steel wire is 9.0. Consider sag and bracing and multiply by 1.03. The corresponding formula is: mass = density X volume. Volume = base area x height.

12. Generator principle and right hand rule

The wire crosses magnetic field lines, and inductive magnetism is created inside. When a wire is connected to a closed circuit, current flows through it. Use your right hand to determine direction of flow and extend your right hand to form a plane. Wire movements of thumbs, palms facing N extremes. The direction of four fingers is current, and this end is also positive end.

13. Kirchhoff's first law, second law

Kirchhoff is a celebrity, he invented laws of electrical circuits. The nodal current is first, and outflow and inflow of two phases are equal. The loop voltage is second, and voltage drop and potential are equal.

14. Calculation of total resistance after series and parallel connection of resistors

The value of series of resistors increases, longer series, greater resistance. When connected in parallel, resistance value decreases and corresponding cross section increases. It is difficult to find impedance of a parallel connection, and reciprocal of each value is required first. The reciprocal of reciprocals is resistance after parallel connection. Only two resistors are connected in parallel and total resistance can be calculated with a simple formula. The product of two resistances is used as numerator and sum of two resistances is used as denominator.

15. Solution and Appearance of Three-Phase AC

There are two ways of three-phase connection: delta and star. An angular three-phase circle surrounds circle, and its three vertices are three-phase lines. The star connects with three tails at one point, and connection point is called neutral point. Three terminals lead to a three-phase line, and middle point leads to a neutral line. The phase line is commonly known as live line and neutral line is usually known as neutral line. There are two types of wires for star connection: three-phase, three-wire and four-wire. Three-phase three-wire does not have a neutral wire, and three-phase four-wire has a neutral wire.

16. Evaluation of positive and negative poles of a rectifier diode

A diode has two poles: an anode and a cathode. Distinguishing polarity is relatively easy, firstly, you can see label on graph. One end of triangle is extremely negative, one end of short rod is anode, and rounder end is anode. The larger size has a screw with an anode at one end of screw. If you are worried about using a multimeter to measure, multimeter is ready. Two handles multiplied by one hundred resistance files, respectively nconnected to electrodes. The resistance value is compared twice in front and behind, and one large and one small resistance is carefully recorded. When resistance value is small, look at meter knob, and red positive and black negative electrodes are fixed.

17. Bridge Rectifier Circuit Connection Method

Single-phase bridge type of four tubes, two in series and then in parallel. The two ends of parallel connection output DC current, and two tubes are connected to power supply. Three-phase bridge type six tubes, two in series and then in parallel. The two ends of parallel connection output DC current, and two tubes are connected to power supply. RC protection diode, three connection methods to choose from. One is parallel to AC side and other is parallel to DC side. There are more complicated ones, and at both ends of each tube. Back EMF of inductive load, parallel continuous diode.

18. Magnets and their properties, magnetic fields and lines of force

Regardless of size and thickness, magnets have two poles. South pole S north pole N, maximum magnetic field strength at both ends. The same polarity repels, different polarity attracts, all according to same principle. Describe magnetic field lines, each of which is a closed line. N to S poles in vitro and S to N in vivo. The lines do not cross each other and are relatively dense at both ends.

19. Filter circuit tuned to reduce output current ripple

In order to get a stable flow, a filter circuit is connected to output. One capacitor and one reactance are connected in a T-shaped circuit. Two capacitors and one reactance are called circular circuits. There is a simpler one, two capacitors and one resistor.

20. Influence and method of adjusting deviation of brush from neutral line

When turning on and off excitation, device should be checked at same time. The arrow of tool swings back and forth, and swing is relatively large, and brush is displaced. Gently rotate brush holder until minimum swing is adjusted. The motor is energized for forward and reverse rotation, and two speeds are subtracted. If resulting difference is large, it means that brush is misaligned. Gently rotate brush holder, difference is smallest adjustment.

If you don't accumulate steps, you won't be able to cover thousands of miles; if you don't accumulate little streams, you won't be able to form rivers. To be a good electrician, you must learn basic theory and then put it into practice. Develop good homework habits, don't be opportunistic, hard work will always pay off.