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Transcription:

Preface...x Chapter 1 Electrical Fundamentals Unit 1 Matter...3 Introduction...3 1.1 Matter...3 1.2 Atomic Theory...3 1.3 Law of Electrical Charges...4 1.4 Law of Atomic Charges...5 Negative Atomic Charge...5 Positive Atomic Charge...5 1.5 Charged Material (Static Charge)...5 Static Voltage...6 Reducing Static Charge...6 1.6 Neutralizing a Charge...6 1.7 Lightning...7 1.8 Lightning Protection...7 Unit 1 Summary...9 Unit 1 Conclusion...10 Unit 1 Practice Questions...11 Unit 2 Electron Theory...15 Introduction...15 2.1 Electron Orbits...15 2.2 Valence Electrons...16 2.3 Freeing Electrons from an Atom...16 2.4 Conductors...16 2.5 Insulators...17 2.6 Semiconductors...17 2.7 Atomic Bonding...17 2.8 Compounds...17 Unit 2 Summary...19 Unit 2 Conclusion...20 Unit 2 Practice Questions...21 Unit 3 Magnetism...23 Introduction...23 3.1 The Natural Magnet...23 3.2 Magnetic Polarities...23 3.3 Magnetic Compass...23 3.4 Magnetic Molecule...24 3.5 Magnetic Properties...24 3.6 How to Magnetize Iron...24 3.7 Permanent and Temporary Magnets...24 3.8 Demagnetizing Magnets...25 3.9 Magnetic Lines of Force...25 3.10 Magnetic Materials...25 3.11 Law of Attraction and Repulsion...25 3.12 Retentivity...26 3.13 Permeability...26 Unit 3 Summary...27 Unit 3 Conclusion...28 Unit 3 Practice Questions...29 Unit 4 Electricity...33 Introduction...33 4.1 Electrical Current Flow (Electricity)...33 4.2 Electricity...34 Chemical Activity (Electrochemistry)...34 Magnetism (Magnetoelectricity)...34 Light (Photoelectricity)...35 Thermo Energy (Thermoelectricity)...36 Pressure (Piezoelectricity)...36 4.3 Useful Purposes of Electricity...37 Electrochemistry...37 Electromagnetism...37 Heat (Resistance)...38 Illumination (Lighting)...38 4.4 Danger of Electricity...39 Understanding Electrical Shock Hazard...39 What Determines the Severity of Electrical Shock?...39 Clearing a Ground Fault...40 Fire...41 Electrical Arc Blast...41 4.5 National Electrical Code...42 Unit 4 Summary...43 Unit 4 Conclusion...45 Unit 4 Practice Questions...46 Unit 5 Electromagnetism...49 Introduction...49 5.1 Electromagnetism in a Wire...49 5.2 Field Intensity...50 5.3 Field Interaction...50 5.4 Field Interaction of Loops...50 iv iv

5.5 Electromagnetism in a Coil...51 5.6 Magnetic Core...51 5.7 Ampere and Turns...51 Unit 5 Summary...52 Unit 5 Conclusion...53 Unit 5 Practice Questions...54 Unit 6 Uses of Electromagnetism...57 Introduction...57 6.1 Basic Electric Meters...57 Voltmeter...58 DC Voltmeter...58 DC Ammeter...58 Clamp-on AC Ammeter...59 Ohmmeters...60 Wheatstone Bridge...60 Megohmmeter...60 6.2 Electric Motor...60 Motor Components...60 Understanding Motor Motion...61 6.3 Electrical Generator...62 DC Generator...62 AC Generator...62 6.4 Electromagnetic Relay...63 Contacts...63 Holding Relay...64 Unit 6 Summary...65 Unit 6 Conclusion...67 Unit 6 Practice Questions...68 Chapter 1 Final Exam...70 Chapter 2 Basic Electricity Unit 7 The Electrical Circuit...77 Introduction...77 7.1 The Electrical Circuit...77 7.2 Electron Current Flow Theory...78 7.3 Conventional Current Flow Theory...78 7.4 Voltage (Pressure)...78 7.5 Resistance...79 Conductor Resistance...79 7.6 Electric Current...80 7.7 Power...80 7.8 Electrical Formulas...80 Unit 7 Summary...81 Unit 7 Conclusion...82 Unit 7 Practice Questions...83 Unit 8 Math...85 Introduction...85 8.1 Whole Numbers...85 8.2 Decimal...85 8.3 Fractions...85 8.4 Percentages...86 8.5 Multiplier...86 8.6 Percent Increase...87 8.7 Reciprocals...87 8.8 Squaring a Number...88 8.9 Square Root...89 8.10 Volume...89 8.11 Kilo...89 8.12 Rounding Off...90 8.13 Parentheses...90 8.14 Testing Your Answer for Reasonableness...91 Unit 8 Summary...92 Unit 8 Conclusion...93 Unit 8 Practice Questions...94 Unit 9 Electrical Formulas...99 Introduction...99 9.1 Electrical Circuit...99 9.2 Power Source...100 Direct Current...100 Alternating Current...100 9.3 Conductance...100 9.4 Circuit Resistance...101 9.5 Ohm s Law...101 9.6 Ohm s Law and Alternating Current...102 Direct Current...102 Alternating Current...102 9.7 Ohm s Law Formula Circle...102 9.8 PIE Formula Circle...103 9.9 Formula Wheel...104 9.10 Using the Formula Wheel...104 9.11 Power Losses of Conductors...105 9.12 Cost of Power...106 9.13 Power Changes with the Square of the Voltage...107 Power Example at 230V...107 Power Example at 208V...107 Power Example at 240V...108 Unit 9 Summary...109 Unit 9 Conclusion...110 Unit 9 Practice Questions...111 Chapter 2 Final Exam...115 v v

Chapter 3 Basic Electrical Circuits Unit 10 Series Circuits...123 Introduction...123 10.1 Practical Uses of the Series Circuit...123 Lighting...123 Control Circuit...124 Signaling Circuit...124 Internal Equipment Wiring...124 10.2 Understanding Series Calculations...124 Resistance...124 Voltage...125 Kirchoff s Voltage Law...125 Kirchoff s Current Law...126 Power...127 10.3 Series Circuit Calculations...127 10.4 Power Calculations...128 10.5 Variations...128 10.6 Series Circuit Notes...128 10.7 Series-Connected Power Supplies...128 Unit 10 Summary...130 Unit 10 Conclusion...131 Unit 10 Practice Questions...132 Unit 11 Parallel Circuits...135 Introduction...135 11.1 Practical Uses of the Parallel Circuit...135 Receptacle...135 Lighting...135 Other Uses...135 11.2 Understanding Parallel Calculations...137 Voltage...137 Kirchoff s Current Law...137 Power...138 11.3 Circuit Resistance...138 Equal Resistance Method...138 Product-Over-Sum Method...139 Reciprocal Method...140 11.4 Parallel Circuit Notes...140 11.5 Parallel-Connected Power Supplies...141 Unit 11 Summary...142 Unit 11 Conclusion...143 Unit 11 Practice Questions...144 Unit 12 Series-Parallel Circuits...147 Introduction...147 12.1 Review of Series and Parallel Circuits...147 Series Circuit Review...147 Parallel Circuit Review...148 12.2 Working Series-Parallel Circuits...148 12.3 Voltage...149 Unit 12 Summary...150 Unit 12 Conclusion...151 Unit 12 Practice Questions...152 Unit 13 Multiwire Circuits...153 Introduction...153 13.1 Neutral Conductor...153 13.2 Grounded Conductor...154 13.3 Current Flow on the Grounded (Neutral) Conductor...154 2-Wire Circuit...154 3-Wire, 120/240V, Single-Phase Circuit...154 13.4 Balanced Systems...155 13.5 Unbalanced Current...155 3-Wire, 120/240V, Single-Phase Circuit...155 3-Wire Circuit from a 4-wire, Three-Phase System...156 4-Wire, Three-Phase Circuit...156 13.6 Multiwire Branch Circuit...156 2-Wire Circuit Voltage Drop...157 Multiwire Circuit Voltage Drop...157 13.7 Dangers of Multiwire Circuits...158 Fire Hazard...158 Destruction of Equipment as Well as Fire Hazard...158 13.8 NEC Requirements...159 Unit 13 Summary...160 Unit 13 Conclusion...161 Unit 13 Practice Questions...162 Chapter 3 Final Exam...165 Chapter 4 Electrical Systems and Protection Unit 14 The Electrical System...173 Introduction...173 14.1 Current Flow...173 14.2 Utility Neutral Current Path...173 Multipoint Neutral Ground...173 14.3 Utility Ground-Fault Current Path...174 14.4 Premises Neutral Current Path...174 Single Point Neutral Bond...175 14.5 Premises Ground-Fault Current Path...175 Earth as Ground Fault Path for Systems 600V or Less...175 vi vi

14.6 Utility High-Voltage Transmission Lines...175 14.7 Conductor Voltage Drop...175 14.8 Conductor Power Loss...176 Current...176 14.9 Reducing Voltage Drop and Power Loss...177 138 kv Transmission Line...177 14.10 Generating Plants...177 14.11 Step-Up Substation at Generating Plant...177 14.12 Transmission Line...178 14.13 Step-Down Substation...178 14.14 Primary Distribution Feeders...178 14.15 Distribution Transformer...178 14.16 Secondary Distribution Line...178 Unit 14 Summary...179 Unit 14 Conclusion...181 Unit 14 Practice Questions...182 Unit 15 Protection Devices...185 Introduction...185 Part A Overcurrent Protection Devices...185 15.1 Overcurrent Protection...185 Overload...185 Ground Fault...186 Short Circuit...186 15.2 Clearing Faults...186 Time Current Curves...186 Remove Dangerous Touch Voltage...186 15.3 Overcurrent Protection Device Types...187 15.4 Fuse...187 Construction...187 Overload Protection...187 Short-Circuit and Ground-Fault Protection...187 15.5 Circuit Breaker Trip Elements...188 Thermal Trip Element...188 Magnetic Trip Element...188 15.6 Circuit Breaker Types...188 Inverse-Time...188 Adjustable-Trip...188 Instantaneous-Trip...188 15.7 Available Short-Circuit Current...188 15.8 Interrupting Rating...189 15.9 Short-Circuit Current Rating...190 15.10 Current-Limiting Protection...190 Part B Ground-Fault Circuit Interrupters...191 15.11 How a GFCI Works...191 15.12 Neutral-to-Case Detection...191 15.13 Line-to-Neutral Shock Hazard...192 15.14 GFCI Fails Circuit Remains Energized...192 15.15 GFCI Test Button...193 Part C Arc-Fault Circuit Interrupter...193 15.16 Arcing Definition...193 15.17 Series Versus Parallel Arc...193 Series Arc...193 Parallel Arc...193 15.18 AFCI and the NEC...194 15.19 AFCI How They Operate...194 Part D Ground-Fault Protection of Equipment...194 15.20 Ground-Fault Protection of Equipment Definition...194 Unit 15 Summary...195 Unit 15 Conclusion...198 Unit 15 Practice Questions...199 Chapter 4 Final Exam...205 Chapter 5 Alternating Current Unit 16 Alternating Current...213 Introduction...213 16.1 Current Flow...213 16.2 Why Alternating Current is Used...213 16.3 How Alternating Current is Produced...214 16.4 AC Generator...214 16.5 Waveform...215 Direct-Current Waveform...215 Alternating-Current Waveform...215 16.6 Sine Wave...216 Sinusoidal Waveform...216 Nonsinusoidal Waveform...216 16.7 Nonsymmetrical Waveform...216 16.8 Frequency...216 16.9 Phase...217 16.10 Degrees...217 16.11 Lead or Lag...217 Leading...217 Lagging...217 16.12 Values of Alternating Current...218 Instantaneous Value...218 Peak Value...218 Effective Value...218 RMS Value...218 Unit 16 Summary...219 Unit 16 Conclusion...220 Unit 16 Practice Questions...221 vii vii

Unit 17 Capacitance...225 Introduction...225 Capacitor Current Flow...225 17.1 Charged Capacitor...225 17.2 Electrical Field...226 17.3 Discharging a Capacitor...226 17.4 Determining Capacitance...227 Plate Distance...227 Surface Area...227 Dielectric Strength...227 17.5 Uses of Capacitors...227 Electronic Power Supplies...228 17.6 Phase Relationship...228 Unit 17 Summary...229 Unit 17 Conclusion...230 Unit 17 Practice Questions...231 Unit 18 Induction...233 Introduction...233 18.1 Self-Induction...233 18.2 Induced Voltage and Applied Current...234 Opposes Current Flow...234 Aids the Current Flow...234 18.3 Conductor AC Resistance...234 Eddy Currents...235 Skin Effect...235 18.4 Impedance...235 18.5 Conductor Shape...235 Current...236 Winding...236 Frequency...236 18.6 Magnetic Cores...236 Core Material...236 Core Length...236 Core Area...236 18.7 Self-Induced and Applied Voltage...237 18.8 Current Flow...237 Inductive Reactance...237 18.9 Phase Relationship...238 18.10 Uses of Induction...238 Unit 18 Summary...239 Unit 18 Conclusion...240 Unit 18 Practice Questions...241 Unit 19 Power Factor and Efficiency...245 Introduction...245 Inductors and Capacitors...245 Part A Power Factor...245 19.1 Apparent Power (Volt-Ampere)...245 19.2 True Power (Watts)...246 Direct Current...246 Alternating Current...246 19.3 Power Factor...246 19.4 Unity Power Factor...246 19.5 Power Factor Formulas...247 19.6 Cost of True Power...248 19.7 Effects of Power Factor...248 Part B Efficiency...250 19.8 Efficiency...250 19.9 Efficiency Formulas...250 Unit 19 Summary...252 Unit 19 Conclusion...253 Unit 19 Practice Questions...254 Chapter 5 Final Exam...257 Chapter 6 Motors, Generators, and Transformers Unit 20 Motors...265 Introduction...265 Part A Motor Basics...265 20.1 Motor Principles...265 Stator...265 Rotor...266 20.2 Dual-Voltage AC Motors...266 20.3 Motor Horsepower Rating...266 20.4 Motor Current Ratings...267 Motor Full-Load Ampere (FLA) Rating...267 Actual Motor Current... 267 Motor Full-Load Current (FLC) Rating...267 20.5 Calculating Motor FLA...267 Single-Phase...268 Three-Phase...268 20.6 Motor-Starting Current...269 20.7 Motor-Running Current...269 20.8 Motor Locked-Rotor Current (LRC)...269 20.9 Motor Overload Protection...269 NEC Requirement...270 Part B Direct-Current Motors...270 20.10 Direct-Current Motor Principles...270 20.11 Direct-Current Motor Types...271 Shunt-Wound DC Motor...271 Series-Wound DC Motor...271 viii viii

20.12 Reversing the Rotation of a DC Motor...271 Part C Alternating-Current Motors...271 20.13 AC Induction Motor...271 20.14 Alternating-Current Motor Types...272 Squirrel-Cage Induction Motor...272 Synchronous Motor...272 Wound-Rotor Motor...272 Universal Motor...273 20.15 Reversing the Rotation of an AC Motor...273 Unit 20 Summary...274 Unit 20 Conclusion...276 Unit 20 Practice Questions...277 Unit 21 Generators...281 Introduction...281 21.1 Direct-Current Generator...281 Excitation Current...281 21.2 Alternating-Current Generator...282 21.3 Three-Phase Generators...283 Unit 21 Summary...284 Unit 21 Conclusion...284 Unit 21 Practice Questions...285 Unit 22 Transformers...287 Introduction...287 22.1 Transformer Basics...287 Primary Versus Secondary...287 Mutual Induction...287 22.2 Secondary Induced Voltage...288 22.3 Autotransformers...288 Step-Down Transformers...288 Step-Up Transformers...289 22.4 Power Losses...289 Conductor Resistance Loss...289 Flux Leakage Loss...289 Eddy Currents...290 Hysteresis Losses...290 22.5 Harmonic Current...290 22.6 Efficiency...291 22.7 Transformer Turns Ratio...291 22.8 Transformer kva Rating...292 22.9 Current Flow...292 22.10 Current Rating...293 Unit 22 Summary...295 Unit 22 Conclusion...296 Unit 22 - Practice Questions...297 Chapter 6 Final Exam...300 Basic Electrical Theory Final Exam...309 Basic Electrical Theory Final Conclusion...324 Annex A Grounding and Bonding Introduction...325 Understanding the Basics of Electrical Systems...326 Understanding Electrical Shock Hazard...328 What Determines the Severity of Electrical Shock...328 Clearing a Ground Fault...329 Why Grounding is Often Difficult to Understand...330 250.1 Scope...333 250.2 Definitions...333 250.3 Other Code Sections...334 250.4 General Requirements for Grounding and Bonding...335 250.4(A) Summary...340 250.6 Objectionable (Neutral) Current...345 Index...347 ix ix

Article 90 Introduction...1 90.1 Purpose of the NEC...1 90.2 Scope of the NEC...2 90.3 Code Arrangement...4 90.4 Enforcement...5 90.5 Mandatory Requirements and Explanatory Material...6 90.6 Formal Interpretations...6 90.7 Examination of Equipment for Product Safety...6 90.9 Units of Measurement...7 Article 90 Questions...8 Chapter 1 General...9 Article 100 Definitions...11 Article 110 Requirements for Electrical Installations...31 Part I. General Requirements...31 110.1 Scope...31 110.2 Approval of Equipment...31 110.3 Examination, Identification, Installation, and Use of Equipment...31 110.4 Voltages...32 110.5 Copper Conductors...32 110.6 Conductor Sizes...32 110.7 Conductor Insulation...33 110.8 Suitable Wiring Methods...33 110.9 Interrupting Protection Rating...33 110.10 Short-Circuit Current Rating...34 110.11 Deteriorating Agents...35 110.12 Mechanical Execution of Work...36 110.13 Mounting and Cooling of Equipment...37 110.14 Conductor Termination...37 110.15 High-Leg Conductor Identification...41 110.16 Flash Protection Warning...42 110.21 Manufacturer s Markings...42 110.22 Identification of Disconnecting Means...43 Part II. 600V, Nominal or Less...43 110.26 Spaces About Electrical Equipment...43 110.27 Guarding...48 Article 110 Questions...49 Chapter 2 Wiring and Protection...51 Article 200 Use and Identification of Grounded Neutral Conductor...53 200.1 Scope...54 200.6 Identification of the Grounded Neutral Conductor...54 200.7 Use of White or Gray Color...56 200.9 Terminal Identification...57 200.10 Identification of Terminals...57 200.11 Polarity...57 Article 200 Questions...58 Article 210 Branch Circuits...59 Part I. General Provisions...59 210.1 Scope...59 210.2 Other Articles...60 210.3 Branch-Circuit Rating...60 210.4 Multiwire Branch Circuits...60 210.5 Identification for Branch Circuits...62 210.6 Branch-Circuit Voltage Limitation...63 210.7 Branch-Circuit Receptacle Requirements...63 210.8 GFCI-Protected Receptacles...64 210.11 Branch-Circuits Required...68 210.12 Arc-Fault Circuit-Interrupter (AFCI) Protection...71 210.18 Guest Rooms and Guest Suites...71 Part II. Branch-Circuit Ratings...71 210.19 Conductor Sizing...71 210.20 Overcurrent Protection...73 210.21 Outlet Device Rating...74 210.23 Permissible Loads...74 210.25 Common Area Branch Circuits...75 vi

Understanding the National Electrical Code, Volume 1 Part III. Required Outlets...75 210.50 General...75 210.52 Dwelling Unit Receptacle Outlet Requirements...75 210.60 Receptacles in Guest Rooms or Guest Suites for Hotels and Motels...81 210.63 Heating, Air-Conditioning, and Refrigeration Equipment (HACR)...82 210.70 Lighting Outlet Requirements...82 Article 210 Questions...85 Article 215 Feeders...87 215.1 Scope...87 215.2 Minimum Rating...87 215.3 Overcurrent Protection...88 215.8 High-Leg Conductor Identification...89 215.10 Ground-Fault Protection of Equipment...89 215.12 Identification for Feeders...89 Article 215 Questions...91 Article 220 Branch-Circuit, Feeder, and Service Calculations...93 Part I. General...93 220.1 Scope...93 220.3 Application of Other Articles...93 220.5 Calculations...94 Part II. Branch-Circuit Load Calculations...94 220.12 General Lighting...94 220.14 Other Loads All Occupancies...95 220.18 Maximum Load on a Branch Circuit...99 Part III. Feeder and Service Calculations...100 220.40 General...100 220.42 General Lighting Demand Factors...100 220.43 Commercial Show Window and Track Lighting Load...100 220.44 Commercial Receptacle Load...101 220.50 Motor Load...101 220.51 Fixed Electric Space-Heating Load...101 220.52 Dwelling Unit Small-Appliance and Laundry Load...102 220.53 Dwelling Unit Appliance Load...102 220.54 Dwelling Unit Electric Clothes Dryer Load...102 220.55 Dwelling Unit Electric Ranges and Cooking Appliances...103 220.56 Commercial Kitchen Equipment Load...104 220.60 Noncoincident Loads...104 220.61 Feeder/Service Neutral Unbalanced Load...104 Part IV. Optional Calculations for Computing Feeder and Service Loads...107 220.82 Dwelling Unit Optional Load Calculation...107 Table of Contents 220.84 Multifamily Optional Load Calculation...108 220.85 Optional Calculation Two Dwelling Units...108 Article 220 Questions...109 Article 225 Outside Wiring...111 Part I General Requirements...111 225.1 Scope...111 225.2 Other Articles...111 225.6 Minimum Size Conductors...112 225.7 Luminaires Installed Outdoors...112 225.15 Supports Over Buildings...112 225.16 Attachment...112 225.17 Masts as Support...113 225.18 Clearances...113 225.19 Clearances from Buildings...113 225.22 Raceways on Exterior Surfaces of Buildings or Other Structures...114 225.26 Trees for Conductor Support...115 Part II. More Than One Building or Structure...115 225.30 Number of Supplies...115 225.31 Disconnecting Means...115 225.32 Disconnect Location...116 225.33 Maximum Number of Disconnects...117 225.34 Grouping of Disconnects...117 225.35 Access to Occupants...117 225.36 Identified as Suitable for Service Equipment...117 225.37 Identification of Multiple Supplies...117 225.38 Disconnect Construction...117 225.39 Rating of Disconnecting Means...117 Article 225 Questions...118 Article 230 Services...119 Part I. General...120 230.1 Scope...120 230.2 Number of Services...120 230.3 Pass Through a Building or Structure...121 230.6 Conductors Considered Outside a Building...121 230.7 Service Conductors Separate from Other Conductors...121 230.8 Raceway Seals...122 230.9 Clearance from Building Openings...122 230.10 Vegetation as Support...123 Part II. Overhead Service-Drop Conductors...123 230.23 Size and Rating...123 230.24 Clearances...123 230.26 Point of Attachment...124 230.27 Means of Attachment...125 230.28 Service Masts Used as Supports...125 vii

Table of Contents Understanding the National Electrical Code, Volume 1 Part III. Underground Service-Lateral Conductors...125 230.31 Size and Rating...125 230.32 Protection Against Damage...125 Part IV. Service Entrance Conductors...125 230.40 Number of Service-Entrance Conductor Sets...125 230.42 Size and Rating...126 230.43 Wiring Methods...126 230.44 Cable Trays...126 230.46 Spliced Conductors...127 230.50 Protection Against Physical Damage Aboveground...127 230.51 Service Cable Supports...127 230.54 Connections at Weatherheads...127 230.56 High-Leg Identification...128 Part V. Service Equipment General...128 230.66 Identified as Suitable for Service Equipment...128 Part VI. Service Equipment Disconnecting Means...129 230.70 General...129 230.71 Number of Disconnects...130 230.72 Grouping of Disconnects...130 230.76 Manual or Power Operated...131 230.79 Rating of Disconnect...131 230.82 Equipment Connected to the Supply Side of the Service Disconnect...131 Part VII. Service Equipment Overcurrent Protection...132 230.90 Overload Protection Required...132 230.95 Ground-Fault Protection of Equipment...133 Article 230 Questions...134 Article 240 Overcurrent Protection...135 Part I. General...136 240.1 Scope...136 240.2 Definitions...136 240.3 Protection of Equipment...137 240.4 Protection of Conductors...137 240.5 Protection of Flexible Cords and Fixture Wires...140 240.6 Standard Ampere Ratings...140 240.10 Supplementary Overcurrent Protection...140 240.13 Ground-Fault Protection of Equipment...141 Part II. Location...141 240.20 Ungrounded Conductors...141 240.21 Overcurrent Protection Location in Circuit...142 240.24 Location of Overcurrent Protection Devices...147 Part III. Enclosures...148 240.32 Damp or Wet Locations...148 240.33 Vertical Position...149 Part V. Plug Fuses, Fuseholders, and Adapters...149 240.51 Edison-Base Fuse...149 240.53 Type S Fuses...149 240.54 Type S Fuses, Adapters, and Fuseholders...149 Part VI. Cartridge Fuses and Fuseholders...149 240.60 General...150 240.61 Classification...150 Part VII. Circuit Breakers...150 240.80 Method of Operation...150 240.81 Indicating...151 240.83 Markings...151 240.85 Applications...152 Article 240 Questions...153 Article 250 Grounding and Bonding...155 Part I. General...155 250.1 Scope...155 250.2 Definitions...156 250.4 General Requirements for Grounding and Bonding...160 250.6 Objectionable Current...164 250.8 Termination of Grounding and Bonding Conductors...168 250.10 Protection of Fittings...168 250.12 Clean Surface...168 Part II. System Grounding and Bonding...168 250.20 Systems Required to be Grounded and Bonded...168 250.24 Grounding and Bonding at Service Equipment...170 250.28 Main Bonding Jumper and System Bonding Jumper...175 250.30 Grounding and Bonding of Separately Derived AC Systems...176 250.32 Buildings or Structures Supplied by a Feeder or Branch Circuit...181 250.34 Generators Portable and Vehicle-Mounted...183 250.36 High-Impedance Grounded Neutral Systems...184 Part III. Grounding Electrode System and Grounding Electrode Conductor...184 250.50 Grounding Electrode System...185 250.52 Grounding (Earthing) Electrodes...185 250.53 Installation of Grounding Electrode System...188 250.54 Supplementary Electrodes...190 250.56 Resistance of Ground Rod Electrode...190 250.58 Common Grounding (Earthing) Electrode...192 250.60 Lightning Protection System Grounding (Earthing) Electrode...192 250.62 Grounding Electrode Conductor Material...193 250.64 Grounding Electrode Conductor Installation...193 viii

Understanding the National Electrical Code, Volume 1 Table of Contents 250.66 Grounding Electrode Conductor Size...195 250.68 Grounding Electrode Conductor Termination...196 250.70 Grounding Electrode Conductor Termination Fitting...197 Part IV. Grounding (Bonding) of Enclosure, Raceway, and Service Cable...197 250.80 Service Enclosures...197 250.86 Other Enclosures...197 Part V. Bonding...198 250.92 Service Bonding...198 250.94 Grounding (Bonding) of Communications Systems...200 250.96 Bonding Other Enclosures...201 250.97 Bonding 277V/480V...202 250.100 Bonding Hazardous (Classified) Locations...203 250.102 Bonding Jumper...203 250.104 Bonding of Piping Systems and Exposed Structural Metal...205 250.106 Lightning Protection System...208 Part VI. Equipment Grounding (Bonding) and Equipment Grounding (Bonding) Conductors...209 250.110 Fixed Equipment Connected by Permanent Wiring Methods General...209 250.112 Fixed Equipment Connected by Permanent Wiring Methods Specific...209 250.114 Equipment Connected by Cord and Plug...209 250.118 Types of Equipment Grounding (Bonding) Conductors...210 250.119 Identification of Equipment Grounding (Bonding) Conductor...212 250.122 Sizing Equipment Grounding (Bonding) Conductor...213 250.126 Identification of Wiring Device Terminals...215 Part VII. Methods of Equipment Grounding (Bonding)...215 250.130 Equipment Grounding (Bonding) Conductor Connections...215 250.134 Grounding (Bonding) Fixed Equipment...216 250.138 Grounding (Bonding) Cord-and-Plug Connected Equipment...217 250.140 Grounding (Bonding) Ranges, Ovens, and Clothes Dryers...217 250.142 Use of Grounded Neutral Conductor for Equipment Grounding (Bonding)...218 250.146 Connecting Receptacle Grounding Terminal to Box...219 250.148 Continuity and Attachment of Equipment Grounding (Bonding) Conductors to Boxes...221 Article 250 Questions...223 Article 280 Surge Arresters...227 Part I. General...227 280.1 Scope...227 280.2 Definition...227 280.3 Number Required...227 280.4 Surge Arrester Selection...227 Part II. Installation...228 280.11 Location...228 280.12 Routing of Conductors...228 Part III. Connecting Surge Arresters...228 280.21 Installed at Services of Less Than 1,000V...228 280.22 Installed on the Load Side of Services of Less Than 1,000V...228 Article 280 Questions...229 Article 285 Transient Voltage Surge Suppressors (TVSSs)...231 Part I. General...231 285.1 Scope...231 285.2 Definition...231 285.3 Uses Not Permitted...231 285.4 Number Required...231 285.5 Listing...232 285.6 Short-Circuit Current Rating...232 Part II. Installation...232 285.11 Location...232 285.12 Routing of Conductors...232 Part III. Connecting Transient Voltage Surge Suppressors...232 285.21 Connection...232 Article 285 Questions...233 Chapter 3 Wiring Methods and Materials...235 Article 300 Wiring Methods...239 Part I. General Requirements...239 300.1 Scope...239 300.3 Conductors...240 300.4 Protection Against Physical Damage...241 300.5 Underground Installations...244 300.6 Protection Against Corrosion and Deterioration...247 300.7 Raceways Exposed to Different Temperatures...248 300.8 Not Permitted in Raceways...249 300.10 Electrical Continuity...249 300.11 Securing and Supporting...250 ix

Table of Contents Understanding the National Electrical Code, Volume 1 300.12 Mechanical Continuity...251 300.13 Splices and Pigtails...252 300.14 Length of Free Conductors...253 300.15 Boxes or Conduit Bodies...254 300.17 Raceway Sizing...255 300.18 Inserting Conductors in Raceways...257 300.19 Supporting Conductors in Vertical Raceways...257 300.20 Induced Currents in Metal Parts...257 300.21 Spread of Fire or Products of Combustion...258 300.22 Ducts, Plenums, and Air-Handling Spaces...259 300.23 Panels Designed to Allow Access...260 Article 300 Questions...262 Article 310 Conductors For General Wiring...265 310.1 Scope...265 310.2 Conductors...265 310.3 Stranded Conductors...265 310.4 Conductors in Parallel...266 310.5 Minimum Size Conductors...267 310.8 Location...267 310.9 Corrosive Conditions...268 310.10 Insulation Temperature Limitation...268 310.12 Conductor Identification...268 310.13 Conductor Construction...269 310.15 Conductor Ampacity...269 Article 310 Questions...275 Article 312 Cabinets, Cutout Boxes, and Meter Socket Enclosures...277 312.1 Scope...277 Part I. Installation...277 312.2 Damp, Wet, or Hazardous (Classified) Locations...277 312.3 Installed in Walls...278 312.4 Repairing Gaps Around Plaster, Drywall, or Plasterboard Edges...278 312.5 Enclosures...278 312.8 Used for Raceway and Splices...279 Article 312 Questions...280 Article 314 Outlet, Device, Pull and Junction Boxes, Conduit Bodies, and Handhole Enclosures...281 Part I. Scope and General...281 314.1 Scope...281 314.3 Nonmetallic Boxes...281 314.4 Metal Boxes...281 314.5 Short-Radius Conduit Bodies...282 Part II. Installation...282 314.15 Damp, Wet, or Hazardous (Classified) Locations...282 314.16 Number of 6 AWG and Smaller Conductors in Boxes and Conduit Bodies...282 314.17 Conductors That Enter Boxes or Conduit Bodies...285 314.20 Boxes Recessed in Walls or Ceilings...285 314.21 Repairing Gaps Around Boxes...286 314.22 Surface Extensions...286 314.23 Support of Boxes and Conduit Bodies...287 314.25 Covers and Canopies...288 314.27 Outlet Box...288 314.28 Boxes and Conduit Bodies for Conductors 4 AWG and Larger...289 314.29 Wiring to be Accessible...291 314.30 Handhole Enclosures...291 Article 314 Questions...293 Article 320 Armored Cable (Type AC)...295 Part I. General...295 320.1 Scope...295 320.2 Definition...295 Part II. Installation...295 320.10 Uses Permitted...295 320.12 Uses Not Permitted...295 320.15 Exposed Work...296 320.17 Through or Parallel to Framing Members...296 320.23 In Accessible Attics or Roof Spaces...296 320.24 Bends...297 320.30 Secured and Supported...297 320.40 Boxes and Fittings...298 320.80 Conductor Ampacities...298 Part III. Construction Specifications...299 320.100 Construction...299 320.108 Equipment Grounding (Bonding)...299 Article 320 Questions...300 Article 330 Metal-Clad Cable (Type MC)...301 Part I. General...301 330.1 Scope...301 330.2 Definition...301 Part II. Installation...301 330.10 Uses Permitted...301 330.12 Uses Not Permitted...302 330.17 Through or Parallel to Framing Members...302 330.23 In Accessible Attics or Roof Spaces...302 330.24 Bends...303 Part II. Installation...303 330.30 Secured and Supported...303 x

Understanding the National Electrical Code, Volume 1 Table of Contents 330.40 Fittings...304 330.80 Conductor Ampacities...304 Part III. Construction Specifications...304 330.108 Equipment Grounding (Bonding)...304 Article 330 Questions...306 Article 334 Nonmetallic-Sheathed Cable (Types NM and NMC)...307 Part I. General...307 334.1 Scope...307 334.2 Definition...307 334.6 Listed...307 Part II. Installation...307 334.10 Uses Permitted...307 334.12 Uses Not Permitted...308 334.15 Exposed...309 334.17 Through or Parallel to Framing Members...309 334.23 Attics and Roof Spaces...310 334.24 Bends...311 334.30 Secured or Supported...311 334.80 Conductor Ampacity...312 Part III. Construction Specifications...313 334.100 Construction...313 334.104 Conductors...313 334.108 Equipment Grounding...313 334.112 Insulation...313 Article 334 Questions...314 Article 336 Power and Control Tray Cable (Type TC)...315 Part I. General...315 336.1 Scope...315 336.2 Definition...315 Part II. Installation...315 336.10 Uses Permitted...315 336.12 Uses Not Permitted...315 Article 336 Questions...316 Article 338 Service-Entrance Cables (Types SE and USE)...317 Part I. General...317 338.1 Scope...317 338.2 Definition...317 Part II. Installation...317 338.10 Uses Permitted...317 338.24 Bends...318 Article 338 Questions...319 Article 340 Underground Feeder and Branch-Circuit Cable (Type UF)...321 Part I. General...321 340.1 Scope...321 340.2 Definition...321 340.6 Listing Requirements...321 Part II. Installation...321 340.10 Uses Permitted...321 340.12 Uses Not Permitted...321 340.24 Bends...322 340.80 Ampacity...322 340.112 Insulation...322 Article 340 Questions...323 Article 342 Intermediate Metal Conduit (Type IMC)...325 Part I. General...325 342.1 Scope...325 342.2 Definition...325 342.6 Listing Requirements...325 Part II. Installation...325 342.10 Uses Permitted...325 342.14 Dissimilar Metals...326 342.20 Trade Size...326 342.22 Number of Conductors...326 342.24 Bends...326 342.26 Number of Bends (360 )...326 342.28 Reaming...326 342.30 Secured and Supported...326 342.42 Couplings and Connectors...328 342.46 Bushings...328 Article 342 Questions...329 Article 344 Rigid Metal Conduit (Type RMC)...331 Part I. General...331 344.1 Scope...331 344.2 Definition...331 344.6 Listing Requirements...331 Part II. Installation...331 344.10 Uses Permitted...331 344.14 Dissimilar Metals...331 344.20 Trade Size...332 344.22 Number of Conductors...332 344.24 Bends...332 344.26 Number of Bends (360 )...332 344.28 Reaming...332 344.30 Secured and Supported...332 344.42 Couplings and Connectors...333 xi

Table of Contents Understanding the National Electrical Code, Volume 1 344.46 Bushings...334 Article 344 Questions...335 Article 348 Flexible Metal Conduit (Type FMC)...337 Part I. General...337 348.1 Scope...337 348.2 Definition...337 348.6 Listing Requirements...337 Part II. Installation...337 348.10 Uses Permitted...337 348.12 Uses Not Permitted...337 348.20 Trade Size...337 348.22 Number of Conductors...338 348.24 Bends...338 348.26 Number of Bends (360 )...338 348.28 Trimming...338 348.30 Secured and Supported...338 348.42 Fittings...339 348.60 Bonding...339 Article 348 Questions...340 Article 350 Liquidtight Flexible Metal Conduit (Type LFMC)...341 Part I. General...341 350.1 Scope...341 350.2 Definition...341 350.6 Listing Requirement...341 Part II. Installation...341 350.10 Uses Permitted...341 350.12 Uses Not Permitted...341 350.20 Trade Size...341 350.22 Number of Conductors...342 350.24 Bends...342 350.26 Number of Bends (360 )...342 350.30 Secured and Supported...342 350.42 Fittings...343 350.60 Bonding...343 Article 350 Questions...344 Article 352 Rigid Nonmetallic Conduit (Type RNC)...345 Part I. General...345 352.1 Scope...345 352.2 Definition...345 Part II. Installation...345 352.10 Uses Permitted...345 352.12 Uses Not Permitted...346 352.20 Trade Size...346 352.22 Number of Conductors...347 352.24 Bends...347 352.26 Number of Bends (360 )...347 352.28 Trimming...347 352.30 Secured and Supported...347 352.44 Expansion Fittings...348 352.46 Bushings...348 352.48 Joints...348 352.60 Grounding (Bonding)...349 Article 352 Questions...350 Article 353 High-Density Polyethylene Conduit (Type HDPE)...351 Part I. General...351 353.1 Scope...351 353.2 Definition...351 353.6 Listing Requirements...351 Part II. Installation...351 353.10 Uses Permitted...351 353.12 Uses Not Permitted...351 353.20 Trade Size...352 353.22 Number of Conductors...352 353.24 Bends How Made...352 353.26 Bends Number in One Run...352 353.28 Trimming...352 353.46 Bushings...352 353.48 Joints...352 353.56 Splices and Taps...352 353.60 Grounding (Bonding)...352 Article 353 Questions...353 Article 354 Nonmetallic Underground Conduit with Conductors (Type NUCC)...355 Part I. General...355 354.1 Scope...355 354.2 Definition...355 354.6 Listing Requirement...355 Part II. Installation...355 354.10 Uses Permitted...355 354.12 Uses Not Permitted...355 354.20 Trade Size...356 354.24 Bends...356 354.26 Number of Bends (360º)...356 354.28 Trimming...356 354.46 Bushings...356 354.48 Joints...356 354.50 Conductor Terminations...356 Article 354 Questions...347 xii

Understanding the National Electrical Code, Volume 1 Article 356 Liquidtight Flexible Nonmetallic Conduit (Type LFNC)...359 Part I. General...359 356.1 Scope...359 356.2 Definition...359 356.6 Listing Requirement...359 Part II. Installation...359 356.10 Uses Permitted...359 356.12 Uses Not Permitted...359 356.20 Trade Size...359 356.22 Number of Conductors...360 356.24 Bends...360 356.26 Number of Bends (360 )...360 356.30 Secured and Supported...360 356.42 Fittings...360 356.60 Grounding (Bonding)...360 Article 356 Questions...361 Article 358 Electrical Metallic Tubing (Type EMT)...363 Part I. General...363 358.1 Scope...363 358.2 Definition...363 358.6 Listing Requirement...363 Part II. Installation...363 358.10 Uses Permitted...363 358.12 Uses Not Permitted...364 358.20 Trade Size...364 358.22 Number of Conductors...364 358.24 Bends...364 358.26 Number of Bends (360 )...364 358.28 Reaming and Threading...365 358.30 Secured and Supported...365 358.42 Coupling and Connectors...365 Article 358 Questions...366 Article 362 Electrical Nonmetallic Tubing (Type ENT)...367 Part I. General...367 362.1 Scope...367 362.2 Definition...367 Part II. Installation...367 362.10 Uses Permitted...367 362.12 Uses Not Permitted...369 362.20 Trade Sizes...369 362.22 Number of Conductors...369 362.24 Bends...370 362.26 Number of Bends (360 )...370 Table of Contents 362.28 Trimming...370 362.30 Secured and Supported...370 362.46 Bushings...370 362.48 Joints...370 362.60 Grounding (Bonding)...370 Article 362 Questions...372 Article 376 Metal Wireways...373 Part I. General...373 376.1 Scope...373 376.2 Definition...373 Part II. Installation...373 376.10 Uses Permitted...373 376.12 Uses Not Permitted...373 376.21 Conductor Maximum Size...373 376.22 Number of Conductors...373 376.23 Wireway Sizing...374 376.30 Supports...374 376.56 Splices and Taps...375 Article 376 Questions...376 Article 378 Nonmetallic Wireways...377 Part I. General...377 378.1 Scope...377 378.2 Definition...377 Part II. Installation...377 378.10 Uses Permitted...377 378.12 Uses Not Permitted...377 378.21 Conductor Maximum Size...377 378.22 Number of Conductors...377 378.23 Wireway Sizing...378 378.30 Supports...378 378.44 Expansion Fittings...378 378.56 Splices and Taps...378 378.60 Grounding (Bonding)...378 Article 378 Questions...379 Article 380 Multioutlet Assembly...381 380.1 Scope...381 380.2 Uses...381 380.3 Through Partitions...381 Article 380 Questions...382 Article 384 Strut-Type Channel Raceways...383 Part I. General...383 384.1 Scope...383 384.2 Definition...383 xiii

Table of Contents Understanding the National Electrical Code, Volume 1 Part II. Installation...383 384.10 Uses Permitted...383 384.12 Uses Not Permitted...383 384.21 Conductor Maximum Size...384 384.22 Number of Conductors...384 384.30 Securing and Supporting...384 384.56 Splices and Taps...384 384.60 Grounding (Bonding)...384 Article 384 Questions...385 Article 386 Surface Metal Raceways...387 Part I. General...387 386.1 Scope...387 386.2 Definition...387 386.6 Listing Requirements...387 Part II. Installation...387 386.10 Uses Permitted...387 386.12 Uses Not Permitted...388 386.21 Size of Conductors...388 386.22 Number of Conductors...388 386.30 Securing and Supporting...388 386.56 Splices and Taps...388 386.60 Grounding (Bonding)...388 386.70 Separate Compartments...388 Article 386 Questions...389 Article 388 Surface Nonmetallic Raceways...391 Part I. General...391 388.1 Scope...391 388.2 Definition...391 388.6 Listing Requirements...391 Part II. Installation...391 388.10 Uses Permitted...391 388.12 Uses Not Permitted...391 388.21 Size of Conductors...391 388.22 Number of Conductors...391 388.56 Splices and Taps...392 388.60 Grounding (Bonding)...392 388.70 Separate Compartments...392 Article 388 Questions...393 Article 392 Cable Trays...395 392.1 Scope...395 392.2 Definition...395 392.3 Uses Permitted...395 392.4 Uses Not Permitted...396 392.6 Installation...396 392.7 Grounding (Bonding)...396 392.8 Cable Installation...397 Article 392 Questions...398 Chapter 4 Equipment for General Use...399 Article 400 Flexible Cords and Flexible Cables...401 400.1 Scope...401 400.3 Suitability...401 400.4 Types of Flexible Cords and Flexible Cables...401 400.5 Ampacity of Flexible Cords and Flexible Cables...401 400.7 Uses Permitted...402 400.8 Uses Not Permitted...403 400.10 Pull at Joints and Terminals...404 400.13 Overcurrent Protection...404 400.14 Protection from Damage...404 Article 400 Questions...405 Article 402 Fixture Wires...402 402.1 Scope...407 402.3 Types...407 402.5 Allowable Ampacity of Fixture Wires...407 402.6 Minimum Size...407 402.7 Raceway Size...407 402.8 Grounded Neutral Conductor...408 402.10 Uses Permitted...408 402.11 Uses Not Permitted...408 402.12 Overcurrent Protection...408 Article 402 Questions...409 Article 404 Switches...411 404.1 Scope...411 404.2 Switch Connections...411 404.3 Switch Enclosures...412 404.4 Wet Locations...412 404.6 Position of Knife Switches...413 404.7 Indicating...413 404.8 Accessibility and Grouping...414 404.9 Switch Cover Plates (Faceplate)...415 404.10 Mounting Snap Switches...415 404.11 Circuit Breakers Used as Switches...415 404.12 Grounding (Bonding) Metal Enclosures...415 404.14 Rating and Use of Snap Switches...416 404.15 Switch Marking...416 Article 404 Questions...417 Article 406 Receptacles, Cord Connectors, and Attachment Plugs Caps...419 406.1 Scope...419 xiv

Understanding the National Electrical Code, Volume 1 406.2 Receptacle Rating and Type...419 406.3 General Installation Requirements...420 406.4 Receptacle Mounting...421 406.5 Receptacle Faceplates...423 406.6 Attachment Plugs, Cord Connectors, and Flanged Surface Devices...423 406.8 Receptacles in Damp or Wet Locations...424 406.10 Connecting Receptacle Grounding Terminal to Box...425 Article 406 Questions...426 Article 408 Switchboards and Panelboards...427 Part I. General...427 408.1 Scope...427 408.3 Arrangement of Busbars and Conductors...427 408.4 Circuit Directory or Circuit Identification...428 408.5 Clearance for Conductor Entering Bus Enclosures...428 408.7 Unused Openings...429 Part III. Panelboards...429 408.34 Classification of Panelboards...429 408.35 Number of Overcurrent Protection Devices...429 408.36 Overcurrent Protection of Panelboard...429 408.37 Panelboards in Damp or Wet Locations...431 408.40 Grounding (Bonding) of Panelboards...431 408.41 Grounded Neutral Conductor Terminations...432 Article 408 Questions...433 Article 410 Luminaires, Lampholders, and Lamps...435 Part I. General...435 410.1 Scope...435 Part II. Luminaire Locations...435 410.4 Luminaires in Specific Locations...435 410.8 Clothes Closets...437 Part III. Luminaire Outlet Boxes and Covers...438 410.12 Outlet Boxes to be Covered...438 410.14 Connection of Electric-Discharge Luminaires...438 Part IV. Luminaire Supports...439 410.15 Supports...439 410.16 Means of Support...440 Part V. Grounding (Bonding)...442 410.18 Exposed Luminaire Parts...442 Part VI. Wiring of Luminaires...442 410.23 Polarization of Luminaires...442 410.30 Cord-Connected Luminaires...442 410.31 Luminaires Used as a Raceway...443 Table of Contents 410.32 Wiring Luminaires Connected Together...443 410.33 Branch-Circuit Conductors and Ballast...443 Part VIII. Lampholders...443 410.47 Screw-Shell Lampholder...443 Part XI. Recessed Luminaires...443 410.65 Thermally Protected...443 410.66 Recessed Luminaire Clearances...444 410.67 Wiring...444 Part XIII. Electric-Discharge Lighting...444 410.73 General...444 410.76 Luminaire Mounting...445 Part XV. Track Lighting...445 410.100 Definition...445 410.101 Installation...445 410.104 Fastening...446 Part XVI. Decorative Lighting and Similar Accessories...446 410.110 Listing of Decorative Lighting...446 Article 410 Questions...447 Article 411 Lighting Systems Operating at 30V or Less...449 411.1 Scope...449 411.2 Definition...449 411.3 Listing Required...449 411.4 Locations Not Permitted...449 411.5 Secondary Circuits...450 Article 411 Questions...451 Article 422 Appliances...453 Part I. General...453 422.1 Scope...453 422.3 Other Articles...453 Part II. Branch-Circuit Requirements...454 422.10 Branch-Circuit Rating...454 422.11 Overcurrent Protection...454 422.12 Fossil Fuel Heating Equipment (Furnaces)...455 422.13 Storage Water Heaters...455 422.15 Central Vacuum...455 422.16 Flexible Cords...456 422.18 Support of Ceiling-Suspended (Paddle) Fans...457 Part III. Disconnect...457 422.31 Permanently Connected Appliance Disconnect...457 422.33 Cord-and-Plug Connected Appliance Disconnect...457 422.34 Unit Switch as Disconnect...458 422.51 Cord-and-Plug Connected Vending Machines...458 Article 422 Questions...459 xv

Table of Contents Understanding the National Electrical Code, Volume 1 Article 424 Fixed Electric Space-Heating Equipment...461 Part I. General...461 424.1 Scope...461 424.3 Branch Circuits...461 424.9 Permanently Installed Electric Baseboard Heaters with Receptacles...462 Part III. Electric Space-Heating Equipment...462 424.19 Disconnecting Means...462 Part V. Electric Space-Heating Cables...462 424.44 Installation of Cables in Concrete or Poured Masonry Floors...462 Part VI. Duct Heaters...462 424.65 Disconnect for Electric Duct Heater Controller...462 Article 424 Questions...464 Article 430 Motors, Motor Circuits, and Controllers...465 Part I. General...465 430.1 Scope...465 430.2 Definitions...466 430.6 Table FLC Versus Motor Nameplate Current Rating...466 430.8 Marking on Controllers...467 430.9 Motor Controller Terminal Requirements...467 430.14 Location of Motors...468 430.17 The Highest-Rated Motors...468 Part II. Conductor Size...468 430.22 Single Motor Conductor Size...468 430.24 Several Motors Conductor Size...469 430.28 Motor Feeder Taps...469 Part III. Overload Protection...469 430.31 Overload...470 430.32 Overload Sizing Continuous-Duty Motors...471 430.36 Use of Fuses for Overload Protection...471 430.37 Number of Overload Devices...472 Part IV. Branch-Circuit Short-Circuit and Ground-Fault Protection...472 430.51 General...472 430.52 Branch-Circuit Short-Circuit and Ground-Fault Protection...472 430.55 Single Overcurrent Protective Device...473 Part V. Feeder Short-Circuit and Ground-Fault Protection...473 430.62 Feeder Protection...473 Part VI. Motor Control Circuits...474 430.72 Overcurrent Protection for Control Circuits...474 430.74 Disconnect for Control Circuit...474 Part VII. Motor Controllers...475 430.83 Controller Rating...475 430.84 Need Not Open All Conductors of the Circuit...475 430.87 Controller for Each Motor...475 430.91 Motor Controller Enclosure Types...476 Part IX. Disconnecting Means...476 430.102 Disconnect Requirement...476 430.103 Disconnect Opens All Conductors...477 430.104 Marking and Mounting...477 430.107 Readily Accessible...477 430.109 Disconnecting Means Rating...477 430.111 Combination Controller-Disconnect...477 Part X. Adjustable-Speed Drive Systems...478 430.120 General...478 430.122 Conductors Minimum Size and Ampacity...478 430.124 Overload Protection...478 430.128 Disconnecting Means...478 Part XIV. Tables...478 Table 430.248 Full-Load Current, Single-Phase Motors...478 Table 430.250 Full-Load Current, Three-Phase Motors...478 Table 430.251 Locked-Rotor Currents...478 Article 430 Questions...479 Article 440 Air-Conditioning and Refrigeration Equipment...481 Part I. General...481 440.1 Scope...481 440.2 Definitions...481 440.3 Other Articles...481 440.4 Marking on Hermetic Refrigerant Motor-Compressors and Equipment...482 440.6 Ampacity and Rating...482 Part II. Disconnecting Means...482 440.14 Location...482 Part III. Circuit Protection...483 440.21 General...483 440.22 Short-Circuit and Ground-Fault Protection Device Size...483 Part IV. Conductor Sizing...484 440.32 Conductor Size One Motor-Compressor...484 440.33 Conductor Size Several Motor-Compressors...485 Part VII. Room Air Conditioners...485 440.62 Branch-Circuit Requirements...485 xvi

Understanding the National Electrical Code, Volume 1 Table of Contents 440.63 Disconnecting Means...485 440.64 Supply Cord...485 440.65 Leakage Current Detection and Interruption, and Arc-Fault Circuit Interrupter...485 Article 440 Questions...486 Article 445 Generators...487 445.1 Scope...487 445.11 Marking...487 445.12 Overcurrent Protection...487 445.13 Ampacity of Conductors...487 445.18 Disconnecting Means...488 Article 445 Questions...490 Article 450 Transformers and Transformer Vaults...491 Part I. General...491 450.1 Scope...491 450.3 Overcurrent Protection...491 450.9 Ventilation...493 450.11 Marking...493 450.13 Transformer Accessibility...493 Part III. Transformer Vaults...493 450.41 Location...493 450.42 Walls, Roofs, and Floors...494 450.43 Doorways...494 450.45 Ventilation Openings...494 450.47 Water Pipes and Accessories...494 450.48 Storage in Vaults...494 Article 450 Questions...495 Article 460 Capacitors...497 460.1 Scope...497 460.2 Enclosing and Guarding...497 Part I. 600V, Nominal, and Under...497 460.8 Conductors...497 460.9 Rating or Setting of Motor Overload Device...497 Article 460 Questions...498 xvii

Article 90 Introduction...1 90.1 Purpose of the NEC...1 90.2 Scope of the NEC...2 90.3 Code Arrangement...4 90.4 Enforcement...5 90.5 Mandatory Requirements and Explanatory Material...6 90.6 Formal Interpretations...6 90.7 Examination of Equipment for Product Safety...6 90.9 Units of Measurement...7 Article 90 Questions...8 Chapter 1 General...9 Article 100 Definitions...11 Article 100 Questions...29 Article 110 Requirements for Electrical Installations...31 Part I. General Requirements...31 110.1 Scope...31 110.2 Approval of Equipment...31 110.3 Examination, Identification, Installation, and Use of Equipment...31 110.4 Voltages...32 110.5 Copper Conductors...32 110.6 Conductor Sizes...32 110.7 Conductor Insulation...33 110.8 Suitable Wiring Methods...33 110.9 Interrupting Protection Rating...33 110.10 Short-Circuit Current Rating...34 110.11 Deteriorating Agents...35 110.12 Mechanical Execution of Work...36 110.13 Mounting and Cooling of Equipment...37 110.14 Conductor Termination...37 110.15 High-Leg Conductor Identification...41 110.16 Flash Protection Warning...42 110.21 Manufacturer s Markings...42 110.22 Identification of Disconnecting Means...43 Part II. 600V, Nominal or Less...43 110.26 Spaces About Electrical Equipment...43 110.27 Guarding...48 Article 110 Questions...49 Chapter 5 Special Occupancies...501 Article 500 Hazardous (Classified) Locations...503 500.1 Scope Articles 500 Through 504...503 500.2 Definitions...504 500.3 Other Articles...505 500.4 General...505 500.5 Classifications of Locations...505 500.6 Material Groups...507 500.7 Protection Techniques...508 500.8 Equipment...509 500.9 Specific Occupancies...511 Article 500 Questions...512 Article 501 Class I Hazardous (Classified) Locations...513 Part I. General...513 501.1 Scope...513 501.5 General...513 Part II. Wiring...513 501.10 Wiring Methods...513 501.15 Conduit and Cable Seals...515 501.20 Conductor Insulation...519 501.30 Bonding...519 501.35 Surge Protection...520 501.40 Multiwire Branch Circuits...520 Part III. Equipment...520 501.100 Transformers and Capacitors...520 501.105 Meters, Instruments, and Relays...521 501.115 Enclosures...521 501.120 Control Transformers and Relays...521 501.125 Motors and Generators...521 501.130 Luminaires...522 vi

Understanding the National Electrical Code, Volume 2 Table of Contents 501.140 Flexible Cords...523 501.145 Receptacles and Attachment Plugs...523 501.150 Low-Voltage, Limited-Energy, and Communications Systems...523 Article 501 Questions...525 Article 502 Class II Hazardous (Classified) Locations...527 Part I. General...527 502.1 Scope...527 502.5 General...527 Part II. Wiring...528 502.10 Wiring Methods...528 502.15 Seals...529 502.30 Bonding...529 502.35 Surge Protection...530 502.40 Multiwire Branch Circuits...530 Part III. Equipment...530 502.115 Switches, Circuit Breakers, Motor Controllers, and Fuses...530 502.120 Control Transformers...531 502.125 Motors and Generators...531 502.130 Luminaires...532 502.140 Flexible Cords...532 502.145 Receptacles and Attachment Plugs...532 502.150 Low-Voltage, Limited-Energy, and Communications Systems...532 Article 502 Questions...534 Article 503 Class III Hazardous (Classified) Locations...535 Part I. General...535 503.1 Scope...535 503.5 General...535 Part II. Wiring...535 503.10 Wiring Methods...535 503.30 Bonding...535 Part III. Equipment...536 503.115 Switches, Circuit Breakers, Motor Controllers, and Fuses...536 503.120 Control Transformers...536 503.125 Motors and Generators...536 503.130 Luminaires...536 503.140 Flexible Cords...537 503.145 Receptacles and Attachment Plugs...537 503.150 Signaling, Alarm, Remote-Control, and Loudspeaker Systems...537 Article 503 Questions...538 Article 504 Intrinsically Safe Systems...539 504.1 Scope...539 504.2 Definitions...539 504.3 Application of Other Articles...539 504.4 Equipment Approval...539 504.10 Equipment Installation...539 504.20 Wiring Methods...540 504.30 Separation of Intrinsically Safe Circuits...540 504.50 Grounding (Earthing)...540 504.60 Bonding...540 504.70 Sealing...540 504.80 Identification...540 Article 504 Questions...542 Article 511 Commercial Garages, Repair, and Storage...543 511.1 Scope...543 511.3 Classification of Hazardous Areas...543 511.4 Wiring and Equipment in Hazardous (Classified) Locations...545 511.7 Wiring and Equipment Above Hazardous (Classified) Locations...546 511.9 Seals...546 511.10 Special Equipment...547 511.12 GFCI-Protected Receptacles...547 Article 511 Questions...548 Article 513 Aircraft Hangars...549 513.1 Scope...549 513.3 Classification of Locations...549 513.4 Wiring and Equipment in Class I Locations...549 513.7 Wiring Not Within Class I Locations...549 513.8 Wiring in or Under Hangar Floor...550 513.9 Sealing...550 513.12 GFCI-Protected Receptacles...550 513.16 Bonding...550 Article 513 Questions...551 Article 514 Motor Fuel Dispensing Facilities...553 514.1 Scope...553 514.2 Definition...553 514.3 Classification of Locations...553 514.4 Wiring and Equipment Within Class I Locations...554 514.7 Wiring and Equipment Above Class I Locations...554 514.8 Underground Wiring...555 514.9 Raceway Seal...555 514.11 Emergency Dispenser Disconnects...556 514.13 Maintenance and Service of Dispensing Equipment...556 vii

Table of Contents Understanding the National Electrical Code, Volume 2 514.16 Grounding (Bonding)...557 Article 514 Questions...558 Article 517 Health Care Facilities...559 Part I. General...559 517.1 Scope...559 517.2 Definitions...559 Part II. Wiring and Protection...560 517.10 Applicability...560 517.12 Wiring Methods...560 517.13 Grounding (Bonding) Equipment in Patient Care Areas...560 517.16 Isolated Ground Receptacles...562 517.18 General Care Areas...562 517.30 Essential Electrical Systems for Hospitals...563 Article 517 Questions...565 Article 518 Assembly Occupancies...567 518.1 Scope...567 518.2 General Classifications...567 518.3 Other Articles...567 518.4 Wiring Methods...567 Article 518 Questions...569 Article 525 Carnivals, Circuses, Fairs, and Similar Events...571 Part I. General Requirements...571 525.1 Scope...571 525.3 Other Articles...571 525.5 Overhead Conductor Clearances...571 525.6 Protection of Electrical Equipment...572 Part II. Power Sources...572 525.10 Services...572 525.11 Multiple Sources of Supply...572 525.20 Wiring Methods...572 525.21 Rides, Tents, and Concessions...573 525.22 Outdoor Portable Distribution or Termination Boxes...573 525.23 GFCI-Protected Receptacles and Equipment...573 Part IV. Grounding and Bonding...574 525.30 Equipment Bonding...574 525.31 Equipment Grounding (Bonding)...574 525.32 Grounding (Bonding) Conductor Continuity Assurance...574 Article 525 Questions...575 Article 547 Agricultural Buildings...577 547.1 Scope...577 547.2 Definitions...577 547.5 Wiring Methods...578 547.10 Equipotential Planes and Bonding of Equipotential Planes...579 Article 547 Questions...580 Article 550 Mobile Homes, Manufactured Homes, and Mobile Home Parks...581 Part I. General...581 550.1 Scope...581 550.2 Definitions...581 550.4 General Requirements...582 550.13 Receptacle Outlets...582 550.25 Arc-Fault Circuit-Interrupter (AFCI) Protection...583 Part III. Services and Feeders...583 550.30 Distribution Systems...583 550.31 Allowable Demand Factors...583 550.32 Disconnect...584 550.33 Feeder...585 Article 550 Questions...586 Article 551 Recreational Vehicles and Recreational Vehicle Parks...587 Part I. General...587 551.1 Scope...587 551.2 Definitions...587 551.3 Other Articles...587 Part VI. Recreational Vehicle Parks...587 551.71 Type of Receptacles Required...587 551.73 Calculated Load...587 551.79 Clearance for Overhead Conductors...588 Article 551 Questions...589 Article 555 Marinas and Boatyards...591 555.1 Scope...591 555.2 Definitions...591 555.5 Transformers...592 555.9 Electrical Connections...592 555.12 Load Calculations for Service and Feeder Conductors...592 555.17 Boat Receptacle Disconnecting Means...592 555.19 Receptacles...593 555.21 Motor Fuel Dispensing Stations...594 555.22 Repair Facilities...594 Article 555 Questions...595 viii

Understanding the National Electrical Code, Volume 2 Table of Contents Article 590 Temporary Installations...597 590.1 Scope...597 590.2 All Installations...597 590.3 Time Constraints...597 590.4 General...598 590.6 Ground-Fault Protection for Personnel...599 Article 590 Questions...602 Chapter 6 Special Equipment...603 Article 600 Electric Signs and Outline Lighting...605 Part I. General...605 600.1 Scope...605 600.2 Definitions...605 600.3 Listing...605 600.4 Markings...606 600.5 Branch Circuits...606 600.6 Disconnects...606 600.9 Location...606 600.10 Portable or Mobile Signs...607 600.21 Ballasts, Transformers, and Electronic Power Supplies...607 Article 600 Questions...609 Article 604 Manufactured Wiring Systems...611 604.1 Scope...611 604.2 Definition...611 604.3 Other Articles...611 604.4 Uses Permitted...611 604.5 Uses Not Permitted...611 604.6 Construction...612 Article 604 Questions...613 Article 605 Office Furnishings (Wired Partitions)...615 605.1 Scope...615 605.2 General...615 605.4 Partition Interconnections...615 605.6 Fixed-Type Partitions...615 605.7 Freestanding-Type Partitions...616 Article 605 Questions...617 Article 620 Elevators, Escalators, and Moving Walks...619 Part I. General...619 620.1 Scope...619 Part III. Wiring...619 620.23 Branch Circuit for Machine Room/Machinery Space...619 620.24 Branch Circuit for Hoistway Pit...619 Part IV. Installation of Conductors...620 620.37 Wiring in Elevator Hoistways and Machine Rooms...620 Part VI. Disconnecting Means and Control...620 620.51 Disconnecting Means...620 Part VIII. Machine Rooms, Control Rooms, Machinery Spaces, and Control Spaces...620 620.85 GFCI-Protected Receptacles...620 Article 620 Questions...622 Article 625 Electric Vehicle Charging Systems...623 Part I. General...623 625.1 Scope...623 625.2 Definitions...623 Part IV. Control and Protection...623 625.22 Personnel Protection System...623 625.25 Loss of Primary Source...624 625.26 Interactive Systems...624 Article 625 Questions...625 Article 630 Electric Welders...627 Part I. General...627 630.1 Scope...627 Part II. Arc Welders...627 630.11 Ampacity of Supply Conductors...627 630.12 Overcurrent Protection...628 630.13 Disconnecting Means...628 Part III. Resistance Welders...628 630.31 Ampacity of Supply Conductors...628 630.32 Overcurrent Protection...629 630.33 Disconnecting Means...629 Article 630 Questions...630 Article 640 Audio Signal Processing, Amplification, and Reproduction Equipment...631 Part I. General...631 640.1 Scope...631 640.2 Definitions...631 640.3 Locations and Other Articles...631 640.4 Protection of Electrical Equipment...632 640.5 Access to Electrical Equipment...632 640.6 Mechanical Execution of Work...632 640.7 Grounding (Earthing) and Bonding...633 640.9 Wiring Methods...633 ix

Table of Contents Understanding the National Electrical Code, Volume 2 640.10 Audio Systems Near Bodies of Water...634 Part II. Permanent Audio System Installations...634 640.21 Use of Flexible Cords and Flexible Cables...634 640.22 Wiring of Equipment Racks...635 640.23 Raceway Fill...635 640.25 Loudspeakers in Fire-Resistance Rated Partitions, Walls, and Ceilings...635 Article 640 Questions...636 Article 645 Information Technology Equipment...637 645.1 Scope...637 645.4 Information Technology Equipment Room...637 645.5 Supply Circuits and Interconnecting Cables...638 645.6 Cables Not in Information Technology Equipment Room...639 645.7 Penetrations...639 645.10 Disconnecting Means...639 645.11 Uninterruptible Power Supplies (UPS)...639 645.15 Grounding (Bonding)...639 Article 645 Questions...640 Article 647 Sensitive Electronic Equipment...641 647.1 Scope...641 647.3 General...641 647.4 Wiring Methods...641 647.6 Grounding (Bonding)...642 647.7 Receptacles...642 Article 647 Questions...643 Article 680 Swimming Pools, Spas, Hot Tubs, Fountains, and Similar Installations...645 Part I. General Requirements for Permanently Installed Pools, Storable Pools, Outdoor Spas, Outdoor Hot Tubs, or Fountains...645 680.1 Scope...645 680.2 Definitions...645 680.3 Other Articles...646 680.7 Cord-and-Plug Connected Equipment...646 680.8 Overhead Conductor Clearance...646 680.9 Electric Water Heater...647 680.10 Underground Wiring Location...647 680.11 Equipment Rooms and Pits...647 680.12 Maintenance Disconnecting Means...647 Part II. Permanently Installed Pools, Outdoor Spas, and Outdoor Hot Tubs...648 680.21 Motors...648 680.22 Area Lighting, Receptacles, and Equipment...649 680.23 Underwater Luminaires...651 680.24 Junction Boxes...652 680.25 Feeders...653 680.26 Equipotential Bonding...654 680.27 Specialized Equipment...655 Part III. Storable Swimming Pool...655 680.30 General...655 680.32 GFCI-Protected Receptacles...655 680.34 Receptacle Locations...656 Part IV. Spas and Hot Tubs...656 680.40 General...656 680.41 Emergency Switch for Spas and Hot Tubs...656 680.42 Outdoor Installations...656 680.43 Indoor Installations...657 680.44 GFCI Protection...658 Part V. Fountains...658 680.50 General...658 680.51 Luminaires, Submersible Pumps, and Other Submersible Equipment...658 680.53 Bonding...659 680.55 Methods of Grounding (Bonding)...659 680.56 Cord-and-Plug Connected Equipment...659 680.57 Signs in or Adjacent to Fountains...659 680.58 GFCI-Protected Receptacles...659 Part VII. Hydromassage Bathtubs...659 680.70 Protection...659 680.71 Other Electric Equipment...660 680.72 Other Electrical Equipment...660 680.73 Accessibility...660 680.74 Bonding...660 Article 680 Questions...661 Article 690 Solar Photovoltaic Systems...663 Part I. General...663 690.1 Scope...663 Article 692 Fuel Cell Systems...665 692.1 Scope...665 692.2 Definitions...665 692.6 Listing Requirement...665 Article 692 Questions...666 Article 695 Fire Pumps...667 695.1 Scope...667 695.3 Power Sources...667 695.4 Continuity of Power...667 695.5 Transformers...668 695.6 Power Wiring...668 x

Understanding the National Electrical Code, Volume 2 695.7 Voltage Drop...669 695.14 Control Wiring...670 Article 695 Questions...671 Table of Contents 701.15 Accessibility...686 701.17 Ground-Fault Protection of Equipment...686 701.18 Coordination...686 Article 701 Questions...687 Chapter 7 Special Conditions...673 Article 700 Emergency Power Systems...675 Part I. General...675 700.1 Scope...675 700.2 Application of Other Articles...676 700.3 Equipment Approval...676 700.4 Tests and Maintenance...676 700.5 Capacity...676 700.6 Transfer Equipment...676 700.8 Signs...677 Part II. Circuit Wiring...677 700.9 Wiring...677 Part III. Sources of Power...677 700.12 General Requirements...677 Part IV. Emergency System Circuits for Lighting and Power...679 700.15 Loads on Emergency Branch Circuits...679 700.16 Emergency Illumination...680 Part VI. Overcurrent Protection...680 700.25 Accessibility...680 700.26 Ground-Fault Protection of Equipment...680 700.27 Coordination...680 Article 700 Questions...681 Article 701 Legally Required Standby Power Systems...683 Part I. General...683 701.1 Scope...683 701.2 Definitions...683 701.3 Application of Other Articles...683 701.4 Equipment Approval...683 701.5 Tests and Maintenance...683 701.6 Capacity and Rating...684 701.7 Transfer Equipment...684 701.9 Signs...684 Part II. Circuit Wiring...684 701.10 Wiring...684 Part III. Sources of Power...684 701.11 Legally Required Standby Systems...684 Part IV. Overcurrent Protection...686 Article 702 Optional Standby Power Systems...689 Part I. General...689 702.1 Scope...689 702.2 Definition...689 702.3 Application of Other Articles...690 702.4 Equipment Approval...690 702.5 Capacity and Rating...690 702.6 Transfer Equipment...690 702.8 Signs...690 Part II. Circuit Wiring...690 702.9 Wiring...690 Part III. Grounding and Bonding...690 702.10 Portable Generator Grounding and Bonding...690 Part IV. Sources of Power...690 702.11 Outdoor Generator Sets...690 Article 702 Questions...692 Article 720 Circuits and Equipment Operating at Less than 50 Volts...693 Article 720 Question...694 Article 725 Class 1, Class 2, and Class 3 Remote- Control, Signaling, and Power-Limited Circuits...695 Part I. General...695 725.1 Scope...695 725.2 Definitions...696 725.3 Other Articles...697 725.7 Access to Electrical Equipment Behind Panels Designed to Allow Access...701 725.8 Mechanical Execution of Work...701 725.11 Safety-Control Equipment...702 725.15 Circuit Requirements...702 Part II. Class 1 Circuit Requirements...702 725.21 Class 1 Circuit Classifications and Power Source Requirements...702 725.23 Class 1 Circuit Overcurrent Protection...703 725.25 Class 1 Circuit Wiring Methods...703 725.26 Conductors of Different Circuits in Same Cable, Enclosure, or Raceway...703 725.27 Class 1 Circuit Conductors...704 725.28 Number of Conductors in a Raceway...704 xi

Table of Contents Understanding the National Electrical Code, Volume 2 Part III. Class 2 and Class 3 Circuit Requirements...704 725.41 Power Sources for Class 2 and Class 3 Circuits...704 725.42 Equipment Marking...704 725.51 Wiring Methods on Supply Side of the Class 2 or Class 3 Power Source...704 725.52 Wiring Methods on Load Side of the Class 2 or Class 3 Power Source...705 725.55 Separation from Other Systems...705 725.56 Conductors of Different Circuits in Same Cable, Enclosure, or Raceway...707 725.57 Class 2 or Class 3 Cables Exposed to Lightning...708 725.58 Support...708 725.61 Applications of Class 2 and Class 3 Cables...709 Part VI. Listing Requirements...710 725.82 Listing and Marking of Class 2 and Class 3 Cables...710 Article 725 Questions...712 Article 760 Fire Alarm Systems...713 Part I. General...713 760.1 Scope...713 760.2 Definitions...713 760.3 Other Articles...714 760.7 Access to Electrical Equipment Behind Panels Designed to Allow Access...716 760.8 Mechanical Execution of Work...716 760.9 Fire Alarm Circuit and Equipment Grounding (Bonding)...717 760.10 Fire Alarm Circuit Identification...717 760.11 Fire Alarm Circuit Cables Exposed to Lightning...717 760.15 Fire Alarm Circuit Requirements...717 Part II. Nonpower-Limited Fire Alarm (NPLFA) Circuits...717 760.21 GFCI and AFCI Protection...717 760.23 NPLFA Circuit Overcurrent Protection...717 760.25 NPLFA Circuit Wiring Methods...717 760.26 Conductors of Different Circuits in Same Cable, Enclosure, or Raceway...718 760.27 NPLFA Circuit Conductors...718 760.28 Number of Conductors in a Raceway...718 Part III. Power-Limited Fire Alarm (PLFA) Circuits...718 760.41 Power Sources for PLFA Circuits...718 760.42 Equipment Marking...719 760.52 Wiring Methods and Materials on Load Side of the PLFA Power Source...719 760.55 Separation from Other Circuit Conductors...719 760.56 PLFA Circuits, Class 2, Class 3, and Communications Circuits...720 760.58 Support...720 760.61 Applications of Listed PLFA Cables...720 Part IV. Listing Requirements...721 760.81 Listing and Marking of NPLFA Cables...721 760.82 Listing and Marking of PLFA Cables...721 Article 760 Questions...723 Article 770 Optical Fiber Cables and Raceways...725 Part I. General...725 770.1 Scope...725 770.2 Definitions...725 770.3 Locations and Other Articles...726 770.6 Optical Fiber Cables...727 770.9 Types...727 770.12 Raceways for Optical Fiber Cables...728 770.21 Access to Electrical Equipment Behind Panels Designed to Allow Access...728 770.24 Mechanical Execution of Work...729 Part III. Cables Within Buildings...729 770.113 Listing of Optical Fiber Cables...729 770.133 Installation of Optical Fibers and Electrical Conductors...729 770.154 Applications of Listed Optical Fiber Cables and Raceways...730 Part IV. Listing Requirements...731 770.179 Listing Requirements for Optical Fiber Cables...731 770.182 Listing Requirements for Optical Fiber Raceways...732 Article 770 Questions...733 Chapter 8 Communications Systems...735 Article 800 Communications Circuits...737 Part I. General...737 800.1 Scope...737 800.2 Definitions...737 800.3 Other Articles...738 800.18 Installation of Equipment...739 800.21 Access to Electrical Equipment Behind Panels Designed to Allow Access...739 800.24 Mechanical Execution of Work...740 800.44 Overhead Communications Wires and Cables...740 Part II. Conductors Outside and Entering Buildings...741 800.47 Underground Circuits Entering Buildings...741 800.53 Lightning Conductors...741 Part III. Protection...741 xii

Understanding the National Electrical Code, Volume 2 Table of Contents 800.90 Primary Protection...741 800.93 Cable Grounding...741 Part IV. Grounding Methods...741 800.100 Cable and Primary Protector Grounding...741 Part V. Communications Wires and Cables Within Buildings...744 800.110 Raceways for Communications Circuits...744 800.113 Listing of Communications Wires and Cables...744 800.133 Installation of Communications Circuits and Equipment...744 800.154 Applications of Listed Communications Wires, Cables, and Raceways...746 Part VI. Listing Requirements...747 800.179 Communications Wires and Cables...747 800.182 Communications Raceways...748 Article 800 Questions...749 Article 810 Radio and Television Equipment...751 Part I. General...751 810.1 Scope...751 810.3 Other Articles...752 810.4 Community Television Antenna...752 Part II. Receiving Equipment Antenna Systems...752 810.12 Support of Lead-In Cables...752 810.13 Avoid Contact with Conductors of Other Systems...752 810.15 Grounding...753 810.18 Clearances...753 810.20 Antenna Discharge Unit...754 810.21 Grounding Conductors...754 Article 810 Questions...757 Article 820 Community Antenna Television (CATV) and Radio Distribution Systems...759 Part I. General...759 820.1 Scope...759 820.2 Definitions...759 820.3 Locations and Other Articles...760 820.15 Energy Limitations...761 820.21 Access to Electrical Equipment Behind Panels Designed to Allow Access...761 820.24 Mechanical Execution of Work...761 Part II. Cables Outside and Entering Buildings...762 820.44 Overhead Cables...762 820.47 Underground Circuits Entering Buildings...762 Part III. Protection...763 820.93 Grounding Cable...763 Part IV. Grounding Methods...763 820.100 Cable Grounding...763 Part V. Cables Within Buildings...765 820.110 Raceways for Coaxial Cables...765 820.113 Listing and Markings...766 820.133 Installation of Cables and Equipment...766 820.154 Applications of Listed CATV Cables and Raceways...768 Part VI. Listing Requirements...769 820.179 Additional Listing Requirements...769 820.182 CATV Raceways...769 Article 820 Questions...770 Article 830 Network-Powered Broadband Communications Systems...771 Part I. General...771 830.1 Scope...771 830.2 Definitions...772 Article 830 Questions...773 Chapter 9 Tables...775 Table 1 Conductor Fill...775 Table 4 Raceway Dimensions...776 Table 5 Conductor Cross-Sectional Area...777 Table 8 Conductor Properties...778 Table 9 AC Impedance for Conductors in Conduit Tubing...778 Annex C Raceway Fill Tables...779 Table C.1 Maximum Number of THNN/THWN Conductors in EMT...780 Table C.10 Maximum Number of THNN/THWN Conductors in RNC...781 xiii

UNIT 1 ELECTRICIAN S MATH AND BASIC ELECTRICAL FORMULAS...1 Introduction...1 PART A ELECTRICIAN S MATH...1 Introduction...1 1.1 Whole Numbers...1 1.2 Decimal...1 1.3 Fractions...1 1.4 Percentages...2 1.5 Multiplier...2 1.6 Percent Increase...2 1.7 Reciprocals...3 1.8 Squaring a Number...3 1.9 Square Root...4 1.10 Volume...5 1.11 Kilo...5 1.12 Rounding Off...5 1.13 Parentheses...6 1.14 Testing Your Answer for Reasonableness...6 PART B BASIC ELECTRICAL FORMULAS...7 Introduction...7 1.15 Electrical Circuit...7 1.16 Power Source...7 1.17 Conductance...8 1.18 Circuit Resistance...8 1.19 Ohm s Law...9 1.20 Ohm s Law and Alternating Current...9 1.21 Ohm s Law Formula Circle...9 1.22 PIE Formula Circle...11 1.23 Formula Wheel...12 1.24 Using the Formula Wheel...12 1.25 Power Losses of Conductors...13 1.26 Cost of Power...14 1.27 Power Changes with the Square of the Voltage...14 PART C BASIC ELECTRIC METERS...16 Introduction...16 1.28 Voltmeter...16 1.29 DC Voltmeter...16 1.30 DC Ammeter...17 1.31 Clamp-on AC Ammeter...17 1.32 Ohmmeters...18 1.33 Wheatstone Bridge...18 1.34 Megohmmeter...18 Conclusion...19 UNIT 2 ELECTRICAL CIRCUITS...49 Introduction...49 PART A SERIES CIRCUITS...49 Introduction...49 2.1 Practical Uses of the Series Circuit...49 2.2 Understanding Series Calculations...51 2.3 Series Circuit Calculations...53 2.4 Power Calculations...53 2.5 Variations...53 2.6 Series Circuit Notes...53 2.7 Series-Connected Power Supplies...54 PART B PARALLEL CIRCUITS...54 Introduction...54 2.8 Practical Uses of the Parallel Circuit...55 2.9 Understanding Parallel Calculations...56 2.10 Circuit Resistance...57 2.11 Parallel Circuit Notes...59 2.12 Parallel-Connected Power Supplies...59 PART C SERIES-PARALLEL CIRCUITS...59 Introduction...59 2.13 Review of Series and Parallel Circuits...60 2.14 Working Series-Parallel Circuits...60 2.15 Voltage...61 PART D MULTIWIRE BRANCH CIRCUITS...62 Introduction...62 2.16 Neutral Conductor...62 2.17 Grounded Conductor...62 vi

Electrical NEC Exam Preparation Table of Contents 2.18 Current Flow on the Grounded Neutral Conductor...63 2.19 Balanced Systems...64 2.20 Unbalanced Current...64 2.21 Multiwire Branch Circuit...65 2.22 Dangers of Multiwire Circuits...66 2.23 NEC Requirements...67 Conclusion...68 UNIT 3 UNDERSTANDING ALTERNATING CURRENT...97 Introduction...97 PART A UNDERSTANDING ALTERNATING CURRENT...97 Introduction...97 3.1 Current Flow...97 3.2 Why Alternating Current is Used...98 3.3 How Alternating Current is Produced...98 3.4 AC Generator...98 3.5 Waveform...99 3.6 Sine Wave...99 3.7 Nonsymmetrical Waveform...100 3.8 Frequency...100 3.9 Phase...101 3.10 Degrees...101 3.11 Lead or Lag...101 3.12 Values of Alternating Current...101 PART B CAPACITANCE...102 Introduction...102 3.13 Charged Capacitor...102 3.14 Electrical Field...103 3.15 Discharging a Capacitor...103 3.16 Determining Capacitance...103 3.17 Uses of Capacitors...104 3.18 Phase Relationship...105 PART C INDUCTION...105 Introduction...105 3.19 Self-Induction...106 3.20 Induced Voltage and Applied Current...106 3.21 Conductor AC Resistance...106 3.22 Impedance...107 3.23 Conductor Shape...107 3.24 Magnetic Cores...108 3.25 Self-Induced and Applied Voltage...109 3.26 Current Flow...109 3.27 Phase Relationship...109 3.28 Uses of Induction...110 PART D POWER FACTOR...110 Introduction...110 3.29 Apparent Power (Volt-Amperes)...110 3.30 True Power (Watts)...111 3.31 Power Factor...111 3.32 Unity Power Factor...112 3.33 Power Factor Formulas...112 3.34 Cost of True Power...113 3.35 Effects of Power Factor...113 PART E EFFICIENCY...114 Introduction...114 3.36 Efficiency Formulas...115 Conclusion...117 UNIT 4 MOTORS AND TRANSFORMERS...151 Introduction...151 PART A MOTORS...151 Introduction...151 4.1 Motor Principles...152 4.2 Dual-Voltage AC Motors...152 4.3 Motor Horsepower Rating...152 4.4 Motor Current Ratings...153 4.5 Calculating Motor FLA...153 4.6 Motor-Starting Current...154 4.7 Motor-Running Current...155 4.8 Motor Locked-Rotor Current (LRC)...155 4.9 Motor Overload Protection...155 4.10 Direct-Current Motor Principles...155 4.11 Direct-Current Motor Types...156 4.12 Reversing the Rotation of a DC Motor...156 4.13 AC Induction Motor...156 4.14 Alternating-Current Motor Types...157 4.15 Reversing the Rotation of an AC Motor...157 PART B TRANSFORMERS...158 Introduction...158 4.16 Transformer Basics...158 4.17 Secondary Induced Voltage...158 4.18 Autotransformers...159 4.19 Power Losses...159 4.20 Harmonic Current...161 4.21 Efficiency...161 4.22 Transformer Turns Ratio...161 4.23 Transformer kva Rating...163 4.24 Current Flow...163 4.25 Current Rating...163 Conclusion...164 vii

Table of Contents UNIT 5 RACEWAY AND BOX CALCULATIONS...193 Introduction...193 PART A RACEWAY FILL...193 5.1 Understanding the NEC, Chapter 9 Tables...193 5.2 Raceway and Nipple Calculations...198 5.3 Existing Raceway Calculations...199 5.4 Tips for Raceway Calculations...201 PART B OUTLET BOX FILL CALCULATIONS [314.16]...201 5.5 Sizing Box Conductors All the Same Size [Table 314.16(A)]...201 5.6 Conductor Equivalents [314.16(B)]...202 5.7 Sizing Box Different Size Conductors [314.16(B)]...204 PART C PULL BOXES, JUNCTION BOXES, AND CONDUIT BODIES...206 5.8 Pull and Junction Box Size Calculations...207 5.9 Depth of Box and Conduit Body Sizing [314.28(A)(2) Ex]...208 5.10 Junction and Pull Box Sizing Tips...208 5.11 Pull Box Examples...209 Conclusion...210 Electrical NEC Exam Preparation 6.13 Conductor Bundling Ampacity Adjustment Factor [Table 310.15(B)(2)(a)]...251 6.14 Ambient Temperature Correction and Conductor Bundling Adjustment Factors...253 6.15 Current-Carrying Conductors...254 6.16 Conductor Sizing Summary...256 Conclusion...257 UNIT 7 MOTOR CALCULATIONS...285 Introduction...285 7.1 Single Motor Conductors [430.22(A)]...285 7.2 Motor Overcurrent Protection...286 7.3 Overload Protection [430.6(2) and 430.32(A)]...287 7.4 Branch-Circuit Short-Circuit Ground-Fault Protection [430.51]...289 7.5 Feeder Conductor Size [430.24]...291 7.6 Feeder Protection [430.61]...291 7.7 Highest-Rated Motor [430.17]...292 7.8 Motor Calculations Steps...293 7.9 Motor Calculation Review...293 7.10 Motor VA Calculations...296 Conclusion...297 UNIT 6 CONDUCTOR SIZING AND PROTECTION CALCULATIONS...237 Introduction...237 PART A GENERAL CONDUCTOR REQUIREMENTS...237 6.1 Conductor Insulation Property [Table 310.13]...237 6.2 Allowable Conductor Ampacity [310.15]...239 6.3 Conductor Sizing [110.6]...240 6.4 Terminal Ratings [110.14(C)]...240 6.5 Conductors in Parallel [310.4]...242 6.6 Conductor Size Voltage Drop [210.19(A)(1) FPN No. 4 and 215.2(A) FPN No. 2]...244 6.7 Overcurrent Protection [Article 240]...244 6.8 Overcurrent Protection of Conductors General Requirements [240.4]...246 6.9 Overcurrent Protection of Conductors Specific Requirements...247 6.10 Equipment Conductor Size and Protection Examples...248 PART B CONDUCTOR AMPACITY CALCULATIONS...249 6.11 Conductor Ampacity [310.10]...249 6.12 Ambient Temperature Ampacity Correction Factor [Table 310.16]...250 UNIT 8 VOLTAGE-DROP CALCULATIONS...323 Introduction...323 PART A CONDUCTOR RESISTANCE CALCULATIONS...323 8.1 Conductor Resistance...323 8.2 Conductor Resistance Direct-Current Circuits [Chapter 9, Table 8]...325 8.3 Conductor Impedance Alternating-Current Circuits...326 8.4 Alternating-Current Impedance as Compared to Direct-Current Resistance...326 8.5 Impedance [Chapter 9, Table 9]...326 PART B VOLTAGE-DROP CALCULATIONS...329 8.6 Voltage-Drop Considerations...329 8.7 NEC Voltage-Drop Recommendations...329 8.8 Determining Circuit Conductors Voltage Drop...330 8.9 Sizing Conductors to Prevent Excessive Voltage Drop...332 8.10 Limiting Conductor Length to Minimize Voltage Drop...333 8.11 Limiting Current to Limit Voltage Drop...334 8.12 Extending Circuits...335 Conclusion...336 viii

Electrical NEC Exam Preparation Table of Contents UNIT 9 DWELLING UNIT CALCULATIONS...365 Introduction...365 PART A GENERAL REQUIREMENTS...365 9.1 General Requirements...365 9.2 Voltages [220.5(A)]...365 9.3 Fraction of an Ampere [220.5(B)]...365 9.4 Small-Appliance Circuits [210.11(C)(1)]...366 9.5 Cooking Equipment Branch Circuit [Table 220.55, Note 4]...367 9.6 Laundry Receptacle(s) Circuit [210.11(C)(2)]...369 9.7 Lighting and Receptacles...369 PART B STANDARD METHOD FEEDER/SERVICE LOAD CALCULATIONS...371 9.8 Dwelling Unit Feeder/Service Load Calculations (Article 220, Part III)...371 9.9 Dwelling Unit Feeder/Service Calculations Examples...372 PART C OPTIONAL METHOD FEEDER/SERVICE LOAD CALCULATIONS...376 9.10 Dwelling Unit Optional Feeder/Service Calculations [220.82]...376 9.11 Dwelling Unit Optional Calculation Examples...377 9.12 Neutral Calculations General [220.61]...378 Conclusion...380 UNIT 10 MULTIFAMILY DWELLING CALCULATIONS...411 Introduction...411 10.1 Multifamily Dwelling Unit Calculations General...411 PART A STANDARD METHOD FEEDER/SERVICE LOAD CALCULATIONS...413 10.2 Multifamily Dwelling Unit Calculation Examples Standard Method...413 10.3 Multifamily Dwelling Unit Calculations Standard Method...419 PART B OPTIONAL METHOD FEEDER/SERVICE LOAD CALCULATIONS...421 10.4 Multifamily Dwelling Unit Calculations [220.84] Optional Method...421 10.5 Multifamily Optional Method Example 1 [220.84]...422 10.6 Multifamily Optional Method Example 2 [220.84]...424 Conclusion...426 UNIT 11 COMMERCIAL CALCULATIONS...455 Introduction...455 PART A GENERAL...455 11.1 General Requirements...455 11.2 Conductor Ampacity [Article 100]...455 11.3 Conductor Overcurrent Protection [240.4]...456 11.4 Voltages [220.5(A)]...456 11.5 Rounding an Ampere [220.5(B)]...456 11.6 Air-Conditioning Branch Circuit...457 11.7 Dryers...458 11.8 Electric Heat...459 11.9 Kitchen Equipment...460 11.10 Laundry Equipment...461 11.11 Lighting Demand Factors [Tables 220.12 and 220.42]...462 11.12 Lighting Without Demand Factors [215.2(A)(1), 230.42(A)(1), and Table 220.12]...462 11.13 Lighting-Miscellaneous...463 11.14 Multioutlet Receptacle Assembly [220.14(H)]...463 11.15 Receptacle VA Load...464 11.16 Banks and Offices General Lighting and Receptacles [220.14(K)]...465 11.17 Signs [220.14(F) and 600.5]...467 PART B STANDARD METHOD FEEDER/SERVICE LOAD CALCULATIONS...467 11.18 Feeder/Service Load Calculation...467 11.19 Neutral Calculations [220.61]...467 PART C EXAMPLES...469 11.20 Bank (120/240V, single-phase)...469 11.21 Marina [555.12]...470 11.22 Mobile/Manufactured Home Park [550.31]...471 11.23 Office Building (277/480V, Three-phase)...472 11.24 Recreational Vehicle Park [551.73]...474 11.25 Restaurant Standard Load Calculation (120/208V, Three-phase)...474 PART D OPTIONAL METHOD FEEDER/SERVICE LOAD CALCULATIONS...476 11.26 New Restaurant Optional Method [220.88]...476 11.27 School Optional Method [220.86]...478 PART E ELECTRIC WELDERS...479 11.28 Arc Welders...479 11.29 Resistance Welders...480 11.30 Light Industrial Calculation...481 Conclusion...482 ix

Table of Contents UNIT 12 DELTA/DELTA AND DELTA/WYE TRANSFORMERS...511 Introduction...511 Definitions...511 12.1 Current Flow...515 PART A DELTA/DELTA TRANSFORMERS...516 12.2 Delta Transformer Voltage...516 12.3 Delta High-Leg...516 12.4 Delta Line Currents...517 12.5 Delta Phase Currents...517 12.6 Delta Phase versus Line Current...518 12.7 Delta Current Triangle...519 12.8 Delta Transformer Balancing...520 12.9 Delta Transformer Sizing...521 12.10 Delta Panel Balancing...521 12.11 Delta Panelboard and Conductor Sizing...521 12.12 Delta Neutral Current...522 12.13 Delta Maximum Unbalanced Load...523 12.14 Delta/Delta Example...523 Electrical NEC Exam Preparation PART B DELTA/WYE TRANSFORMERS...526 12.15 Wye Transformer Voltage...526 12.16 Wye Voltage Triangle...526 12.17 Wye Transformers Current...526 12.18 Wye Line Current...527 12.19 Wye Phase Current...527 12.20 Wye Phase versus Line Current...528 12.21 Wye Transformer Balancing...529 12.22 Wye Transformer Sizing...530 12.23 Wye Panel Balancing...530 12.24 Wye Panelboard and Conductor Sizing...531 12.25 Wye Neutral Current...531 12.26 Wye Maximum Unbalanced Load...532 12.27 Delta/Wye Example...532 12.28 Delta versus Wye...536 Conclusion...536 INDEX...567 x

Introduction...vii Passing the Exam...viii The National Electrical Code...xi About the Author...xvi Unit 1 Review Quiz Articles 90 through 200...1 Practice Quiz Articles 80 through 110...14 Challenge Quiz Articles 90 through Annex C...21 Unit 2 Review Quiz Articles 200 through 230...28 Practice Quiz Articles 200 through 230...41 Challenge Quiz Articles 90 through Annex C...48 Unit 3 Review Quiz Articles 230 through 250...55 Practice Quiz Articles 230 through 250...68 Challenge Quiz Articles 90 through Annex C...75 Unit 4 Review Quiz Articles 250 through 310...82 Practice Quiz Articles 250 through 310...96 Challenge Quiz Articles 90 through Annex C...103 Unit 5 Review Quiz Articles 310 through 342...110 Practice Quiz Articles 310 through 342...124 Challenge Quiz Articles 90 through Annex C...130 Unit 6 Review Quiz Articles 342 through 386...139 Practice Quiz Articles 344 through 386...154 Challenge Quiz Articles 90 through Annex C...161 Unit 7 Review Quiz Articles 386 through 410...168 Practice Quiz Articles 386 through 410...182 Challenge Quiz Articles 90 through Annex C...188 Unit 8 Review Quiz Articles 410 through 500...195 Practice Quiz Articles 410 through 480...209 Challenge Quiz Articles 90 through Annex C...216 Unit 9 Review Quiz Articles 500 through 517...222 Practice Quiz Articles 500 through 517...236 Challenge Quiz Articles 90 through Annex C...245 Unit 10 Review Quiz Articles 517 through 645...251 Practice Quiz Articles 517 through 640...267 Challenge Quiz Articles 90 through Annex C...274 Unit 11 Review Quiz Articles 645 through 701...281 Practice Quiz Articles 645 through 701...295 Challenge Quiz Articles 90 through Annex C...302 Unit 12 Review Quiz Articles 702 through Annex C...308 Practice Quiz Articles 702 through Chapter 9...322 Challenge Quiz Articles 90 through Annex C...328 vi

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