- Preface
- guide

CHAPTER 01 General Electricity

001 What do (+) and (-) voltage mean in electricity?
002 What does it mean to say 'electricity flows'?
003 What does it mean that 'current flows'?
004 Does the current flow from phase L1 to the neutral line (N line)?
005 How does the current flow in a single-phase, two-wire system?
006 What is the difference between single-phase, three-phase, and four-phase?
007 What does single phase 2 wire, single phase 3 wire, 3 phase 3 wire, and 3 phase 4 wire mean?
008 How does 3-phase AC flow?
009 What is the relationship between voltage and current?
010 What is EARTH?
011 What do rated voltage and rated current mean?
012 What is the scope of the phase balance (load sharing)?
013 What does power consumption of home appliances mean?
014 What is the difference between power [W] and power [Wh]?
015 How do I check the insulation when there is no grounding in the distribution board?
016 How do I conduct electricity with one line?
017 Why does the value keep increasing when measuring insulation resistance?
018 What causes damage to the work reel cable?
019 How do I use Hook Meta and Mega?
020 What is the relationship between voltage and wire size?
Why is 190[V] measured in a 220[V] outlet?
022 What is the allowable current of the wire?
023 Why do short circuits occur when working on lighting?
024 What is the role of the stabilizer?
Why does a short circuit occur in the 025 switch?
026 If I use single phase as L1 and L3 in 3 phase, what will be the voltage and phase waveforms?
027 Which is more dangerous, current or voltage?
028 Why is the magnitude between line voltage and line voltage 13 times greater in a Y connection?
029 How do I measure insulation using the neutral wire?
030 What is voltage imbalance ratio?
031 How to calculate apparent [kVA], active [kW], and reactive [kVar] power?
032 What happens to the current value when the voltage increases?
033 Why does the ground voltage rise?
034 What do image current and ground current mean?
035 What happens to the meter when one line is connected to a different generation meter in a single phase?
036 Why is the voltage of L1-N 140[V]?
037 What is the role of reactive power?
038 How can I select the thickness of the main line?
039 What is the relationship between phase voltage and line voltage in a 3-phase, 4-wire Y-connection?
040 What is the power consumption in an RLC circuit?
041 Are capacitors and coils not loads but power storage devices?
042 What should I pay attention to when selecting electrical panel equipment (breakers, magnets, capacitors, etc.) for an air conditioner?
043 How do I measure grounding resistance with a clamp-on grounding resistance meter and how do I obtain the measured value?
044 How do I prevent malfunction due to induction?
045 What is plus and minus ground?
046 If the voltage is the same, does it do the same work?
047 What happens if I connect a 50[Hz] power supply and a 60[Hz] power supply?

CHAPTER 02 Electric Shock

048 Can the neutral wire cause electric shock depending on environmental conditions?
049 What does electric shock separation distance mean?
050 Can I get electrocuted by holding just one wire?
051 If the voltage is different for the same current, is the one with the higher voltage more dangerous for electric shock?
052 Are fluorescent lights still powered on even when the switch is turned off?
053 What is the difference between electric shock caused by leakage current and induced voltage?
054 Is the power that causes electric shock and damage to equipment apparent power or real power?
055 What is TT system grounding?

CHAPTER 03 Leakage Current

056 Where does the leakage current flow?
057 What are the conditions for a fire caused by leakage current?
058 What is ground fault current?
059 What is the standard for leakage current?
060 How do I calculate leakage current using an insulation resistance meter?
061 When it is difficult to measure insulation resistance, why is the leakage current set to 1 [mA] or less?
062 What causes leakage current?
063 15[mA] Why use a high-sensitivity leakage circuit breaker?
064 What is generation leakage current?

CHAPTER 04 Neutral Wire

065 Can I get electrocuted by the current flowing in the neutral wire in a 3-phase 4-wire system?
066 What is the voltage between ground and neutral?
067 I turned off the circuit breaker, but why is there a voltage with the neutral line?
068 Can the N-line be detected with a voltage detector?
069 In a 3-phase 4-wire system, will the load side (heating, lighting) be damaged if the neutral line (N line) is disconnected?
070 What is the difference between neutral ground and N-wire?
071 How do I find the ground and neutral wires in a light wiring diagram?
072 Is it correct to install the neutral wire on the busbar?
073 What is the role of KEPCO's incoming cable line?
074 Is the concentric neutral line of the KEPCO cable connected to the extra-high voltage enclosure correct?
075 What is the current flowing in the neutral wire of a 3-phase, 4-wire system?
076 How do I connect the neutral and ground wires?
077 Can't the neutral wire between transformers be used as COMMON?

CHAPTER 05 Circuit Breaker

078 When using a 3-phase leakage circuit breaker as a single phase, why should only poles L1 and L3 be used?
079 What is the difference between a 3P leakage circuit breaker and a 4P leakage circuit breaker?
Why does the circuit breaker trip when the 080 wire gets hot?
081 Why does the circuit breaker trip when I turn the switch off?
082 Will the ELB be cut off even if the neutral wire is grounded without a secondary load?
083 The insulation resistance is zero (0), so why doesn't the circuit breaker trip?
084 What is the standard for the permissible current of MCCB circuit breakers?
085 How should I read the [rated breaking current] on the circuit breaker nameplate?
086 Why doesn't the circuit breaker trip completely when it trips?
087 Do I need to install a leakage circuit breaker when using 208/120[V]?
088 Is there a problem if I switch the primary and secondary wiring of the leakage circuit breaker?
089 What is the difference between a circuit breaker that trips immediately and one that takes a while to trip?
What does a 090 circuit breaker trip mean?
091 Why do contract power and circuit breakers trip?
092 How do I select a circuit breaker and wires?
093 What happens if I turn off the circuit breaker under heavy load?
094 Why doesn't the circuit breaker trip when the two secondary wires are swapped in the event of a leakage current?
095 What happens if I use 2.5[kA] for the main circuit breaker and branch circuit breaker?
096 Does the MCCB trip only when the rated current of all phases is exceeded?
097 Is the malfunction of the leakage circuit breaker (20[A]) due to an abnormal voltage?
098 Does a 3-phase circuit breaker trip even if overcurrent flows through only one phase?
099 What should be the breaking capacity of the distribution board circuit breaker?
When using the same power load at 100 Y-connection 380[V], is the circuit breaker capacity different when using a 3-wire cable and a 4-wire cable?
What happens if I swap the primary and secondary sides of a 101 MCCB?
How do I interpret the 102 circuit breaker trip curve?
Why is the circuit breaker 3P in the 103 Y-△ transformer?
104 How are ACB standards (AF, AT) selected and notated?

CHAPTER 06 Electric Motor

How do I measure the phase resistance of a 105 motor?
106 When I want to change the direction of rotation in a 3-phase motor, do I only need to change 2 of the 3 phases?
107 How do I determine the EMPR SETTING value?
108 What should I consider when selecting a leakage circuit breaker because the leakage current is large when starting the motor?
What happens if the voltage supplied to the 109 motor is low?
What problems are there when using a 110 3-phase 3-wire 220[V] motor in a 3-phase 4-wire (380[V]/220[V]) system?
111 Why does the motor burn out when a voltage lower than the rated voltage (380 [V]) is applied (220 [V])?
112 The water pump motor is burned out, why does the MCCB not trip but the ACB trip?
If 113 EMPR failure occurs, what is the reason?
114 How do I select the wire size when starting Y-△?
115 How do I wire a 3-phase motor?
116 How do I start an induction motor Y-△?
117 Why is the current during Y-start in the Y-start method 1/3 of that during direct-start?
118 What is the relationship between motor starting current and load?
119 What is the allowable current of the wire when starting Y-△?
How do I select the size of the 120 motor wire?
121 Why do you start the motor with Y-△ or reactor?
122 How do I check for motor coil damage?
123 What is the relationship between motor load and current?
124 What is the relationship between RPM and current of an inverter motor?
125 Why use Y-△ wiring?
Why do the measured values ​​show hunting when checking the insulation or line resistance of the 126 FAN MOTOR?
What happens if you use a motor with a frequency of 50[Hz] at 60[Hz]?
Why does 128 EMPR overload?
129 What is the difference between Y-△ wiring and AUTO TR wiring?
Can I use the 130 mobile reactor 220[V] on 380[V]?
131 Does the capacity of explosion-proof motors vary depending on the explosion-proof temperature rating?
132 What is the thermal capacity of the motor and transformer?

CHAPTER 07 Capacitors

133 What is the unit of the power factor improvement capacitor?
134 What is the relationship between capacitor and current?
135 Why do I have to replace power capacitors so often?
136 How much is the effective power reduction after installing the capacitor?
137 What causes the capacitor voltage to rise?
138 What is power factor?
139 Are there any problems caused by low power factor?
140 What is the change in active power due to current reduction after power factor improvement?
141 How do I check the motor capacitor capacity?
142 Why does the capacitor explode after connecting it to a series reactor?
143 Why is the circuit breaker for capacitors selected at about 1.5 times the rated current?
144 What is the relationship between ground fault current and load current when a grounding capacitor is installed?

CHAPTER 08 TRANSFORMERS

145 What are the phase-to-phase and line-to-line voltages in a Y-connected transformer?
146 Can I clean the inlet transformer?
147 How do I find the primary value of the transformer neutral point CT?
148 Why is the primary cable shield of the molded transformer exposed?
149 What should I be careful about when calculating the capacity of a transformer?
What exactly does the secondary rated voltage of a 150 transformer (440[V]) mean?
151 Why is the transformer neutral grounded on the secondary side of the transformer?
152 How much is the transformer capacity lacking?
153 What is the relationship between transformer wiring diagram and voltage?
154 What is the appropriate temperature for a transformer?
155 What is the no-load current of the transformer?
156 What is the secondary line current of the transformer?
157 What is the neutral point?
158 What happens to the current flow in the event of a ground fault in a Y-connection?
159 Why is the load neutral point voltage not 0[V] in Y connection?
What is the leakage current of the ground wire of the 160 transformer type 2?
161 △Can ground fault current flow through the ground of the wiring?
162 How does the inrush current of a transformer affect the transformer?
163 Is the transformer neutral point NGR ground fault protection relay 51N or 51G?
164 What happens if you connect three single-phase transformers as △-△ and ground one of the secondary phases?
How do I adjust the tap on a 165 mold transformer?

CHAPTER 09 Plumbing Equipment

166 If the voltage of the device is 440[V] at 3-phase 380[V], does this exceed the overvoltage tolerance?
How can I find out the current on the 167 panel?
Can the OCR in the 168 VCB panel be replaced?
How should I interpret the operating characteristic graph curve of the 169 relay?
How do I replace the 170 Main VCB Fulton Switch?
171 How do I replace a switchboard Fulton switch?
172 How does the VS & AS changeover switch circuit work?
173 What is the role of the power failure signal in the 22.9[kV] system?
174 Where does the generator's power outage signal come from?
175 Why is there a difference between the certificate and the regular inspection of substation equipment?
What is 176 LBS?
177 Why is the substation grounding box terminal commonly grounded?
178 What is the difference between direct grounding and multi-grounding?
179 Why are LA and SA installed in the water supply system?
How do I calculate the PT ratio in a 180 distribution system?
How is the 181 CT selected?
182 Why does surge voltage occur?
What is the order of operation in the operation time chart of 183 VCB & ACB?
184 Why is it necessary to disconnect the load when operating a VCB or ACB?
185 Is the operating power of the VCB DC or AC?
How does 186 CT work?
187 What is the difference between PT and CT?
188 Why do I multiply the CT and PT ratios after reading?
Why short circuit the secondary of the 189 CT?
How do I calculate the size of the secondary wire of a 190 CT?
191 How do I calculate the meter multiplier (phase voltage, line voltage)?
192 What is GCT?
193 Where is the CT located in the main circuit breaker of the single-line water supply facility?
What is 194 2CT V-connection?
Why is the 195 ACB tripping?
196 What should be the ground fault current when setting the ACB relay?
197 Why does the MAIN ACB blocking phenomenon occur due to GOCR operation?
How do I calculate the capacity when deploying 198 TIE-ACB?
199 How does the low voltage ACB OCGR work?
What are the effects of tripping due to a ground fault in a 200-volt circuit breaker?
How should I ground when using 201 OCGR?
202 Can a ground fault cause equipment failure in an ungrounded system?
How do I get the setting value of the 203 ACB relay itself?
204 What is the relationship between ACB trip and OCGR operation?
What causes ACB trip due to 205 OCGR operation?
Why install UVT on 206 ACB?
207 What should the breaking capacity of the circuit breaker be?
How do I set the OCGR when setting the relay for a load of only a high-voltage motor using a 208 inverter?
209 Does the temporary water supply facility not have a rectifier?
What does [10P10] mean in 210 ZCT?
211 Why does the upper circuit breaker trip first in the event of a short circuit at the distribution board?
212 What is the meaning of Hansi and Sunsi?
213 Why are large loads affected first during momentary voltage drops (or power system instability)?
How do I check for abnormalities in a 214 CT scan?
What should the OCGR setting value of 215 VCB be?
What is 216 GPT?
How do I select the 217 VCS fuse capacity?
218 Can OCGR and OVR be operated by the third harmonic?

Appendix Main Contents of Electrical Equipment Inspection and Inspection Standards

1.
Honest questions from electricians and answers from electrical engineers.
It contains questions about the difficulties electricians have actually faced and answers to those questions based on the know-how of an electrician.

2.
Easy answers using photos and drawings of field equipment
We have made it possible to understand electricity quickly and accurately through pictures of field equipment related to the question and illustrations that easily show the basic theory.

3.
One line Pick
The key content of each section is summarized in one line so that you can check the main content of the section once more.

4.
A solid foundation of basic theory is laid out in the appendix.
The main contents of the electrical equipment inspection and inspection standards are organized in the appendix, so that you can learn the basic theories of electricity with certainty.

5.
Cafe Free Video Lectures
The facility management mall (https://cafe.naver.com/114er) provides free video lectures using the book.

6.
If you have any questions, please contact the author directly.
If you have any questions about the book, you can contact the author directly through his blog, email, or the cafe he runs.