Chapter 1 Electrical Theory...1

Transcription

1 Electrical Formulas with Sample Calculations Table of Contents Chapter 1 Electrical Theory...1 Unit 1 Electrician s Math and Basic Electrical Formulas...3 Part A Electrician s Math Fractions Kilo Knowing Your Answer Multiplier Parentheses Percentages Percent Increase Percentage Reciprocals Rounding Squaring Square Root...6 Part B Basic Electrical Formulas Electrical Circuit Power Source Conductance and Resistance Electrical Circuit Values Ohm s Law I = E/R Pie Circle Formula Formula Wheel Power Changes with the Square of the Voltage...11 Unit 2 Electrical Circuits...12 Part A Series Circuits...12 Introduction to Series Circuits Understanding Series Calculations...12 Part B Parallel Circuits...13 Introduction to Parallel Circuits Practical Uses of Parallel Circuits Understanding Parallel Calculations Parallel Circuit Resistance Calculations Parallel Circuit Summary...16 Part C Series Parallel and Multiwire Branch Circuits...16 Introduction to Series-Parallel Circuits...16 iv

2 Table of Contents Electrical Formulas with Sample Calculations 2 7 Review of Series and Parallel Circuits Series-Parallel Circuit Resistance Calculations...17 Part D Multiwire Branch Circuits...18 Introduction to Multiwire Branch Circuits Neutral Current Calculations Dangers of Multiwire Branch Circuit...19 Unit 3 Understanding Alternating Current...22 Part A Alternating-Current Fundamentals Current Flow Alternating Current Alternating-Current Generator Waveform Armature Turning Frequency Phase In and Out Phase Differences in Degrees Values of Alternating Current...25 Part B Induction...25 Induction Introduction Induced Voltage and Applied Current Conductor Impedance Induction and Conductor Shape Induction and Magnetic Cores...29 Part C Capacitance...31 Capacitance Introduction Charge, Testing and Discharging...31 Part D Power Factor and Efficiency...33 Power Factor Introduction Apparent Power (Volt-Ampere) Power Factor True Power (Watts) Efficiency...38 Unit 4 Motors and Transformers...42 Part A Motors...42 Motor Introduction Motor Speed Control Reversing a Direct-Current Motor Alternating-Current Motors Reversing Alternating-Current Motors Motor Volt-Ampere Calculations Motor Horsepower/Watts Motor Nameplate Ampere...48 Part B Transformer Basics...50 Transformer Introduction Transformer Primary and Secondary...51 v

3 Electrical Formulas with Sample Calculations Table of Contents 4 9 Transformer Secondary and Primary Voltage Autotransformers Transformer Power Losses Transformer Turns Ratio Transformer kva Rating Transformer Current...53 Chapter 2 National Electrical Code Calculations...57 Unit 5 Raceway, Outlet Box and Junction Boxex Calculations Understanding the NEC, Chapter Raceway and Nipple Calculations Existing Raceway Calculations Tips For Raceway Calculations...65 Part B Outlet Box Fill Calculations...65 Introduction [314.16] Sizing Box Conductors all the Same Size [Table (A)] Conductor Equivalents [314.16(B)] Sizing Box Different Size Conductors [314.16(B)]...67 Part C Pull, Junction Boxes, and Conduit Bodies...69 Introduction Pull and Junction Box Size Calculations Depth of Box and Conduit Body Sizing [314.28(A)(2), Ex.] Junction and Pull Box Sizing Tips...71 Unit 6 Conductor Sizing and Protection Calculations Conductor Insulation Property [Table ] Conductor Allowable Ampacity [310.15] Conductor Sizing [110.6] Terminal Ratings [110.14(C)] Conductors In Parallel [310.4] Conductor Size Voltage Drop [210.19(A) FPN 4 AWG and 215.2(A)(4) FPN 2] Overcurrent Protection [Article 240] Overcurrent Protection of Conductors General Requirements [240.4] Overcurrent Protection of Conductors Specific Requirements Equipment Conductors Size and Protection Examples...78 Part B Conductor Ampacity Calculations Conductor Ampacity [310.10] Ambient Temperature Ampacity Adjustment Factor [Table ] Conductor Bundling Ampacity Adjustment Factor [Table (B) Ambient Temperature and Conductor Bundling Adjustment Factors Current-Carrying Conductors Conductor Sizing Summary...85 vi

4 Table of Contents Electrical Formulas with Sample Calculations Unit 7 Motor Calculations...86 Introduction Motor Branch-Circuit Conductors [430.22(A)] Motor Overcurrent Protection Overload Protection [430.32(A)] Branch-Circuit Short-Circuit Ground-Fault Protection [430.52(C)(1)] Feeder Conductor Size [430.24] Feeder Protection [430.62(A)] Highest-Rated Motor [430.17] Motor Calculations Steps Motor Calculation Review Motor VA Calculations...94 Unit 8 Voltage Drop Calculations...97 Part A Conductor Resistance Calculations Conductor Resistance Conductor Resistance Direct-Current Circuits, [Chap. 9, Table 8] Conductor Impedance Alternating-Current Circuits Alternating-Current Impedance as Compared to Direct-Current Resistance Impedance [Chapter 9, Table 9 of the NEC] Part B Voltage-Drop Calculations Voltage-Drop Considerations NEC Voltage-Drop Recommendations Determining Circuit Conductors Voltage Drop Sizing Conductors to Prevent Excessive Voltage Drop Limiting Conductor Length to Limit Voltage Drop Limiting Current to Limit Voltage Drop Extending Circuits Unit 9 Single Family Dwelling Unit Load Calculations Part A - General Requirements General Requirements Voltages [220.2(A)] Fraction of an Ampere [220.2(B)] Appliance (Small) Circuits [210.11(C)(1)] Cooking Equipment Branch Circuit [Table , Note 4] Laundry Receptacle(s) Circuit [210.11(C)(2)] Lighting and Receptacles Part B - Standard Method Feeder/Service Load Calculations Dwelling Unit Feeder/Service Load Calculations (Part II of Article 220) Neutral Calculations General [220.22] vii

5 Electrical Formulas with Sample Calculations Table of Contents Chapter 3 Advanced NEC Calculations Unit 10 Multifamily Dwelling Units Multifamily Dwelling Unit Calculations Standard Method Multifamily Dwelling Unit Calculations [220.32] Optional Method Multifamily Optional Method Example [220.32] Unit 11 Commercial Load Calculations Part A General Conductor Ampacity [Article 100] Conductor Overcurrent Protection [240.4] Voltages [220.2(A)] Rounding an Ampere [220.2(B)] Part B Loads Air-Conditioning Dryers Electric Heat Kitchen Equipment Lighting Demand Factors [Table 220.3(A) and ] Lighting Without Demand Factors [Table 220.3(A), 215.2(A)(1) and ] Lighting Miscellaneous Multioutlet Receptacle Assembly [220.3(B)(8)] Receptacles VA Load [220.13] Banks and Offices General Lighting and Receptacles Signs [220.3(B)(6) and 600.5] Neutral Calculations [220.22] Part C Load Calculation Examples Marina [555.12] Mobile/Manufactured Home Park [550.31] Recreational Vehicle Park [551.73] Restaurant Optional Method [220.36] School Optional Method [220.34] Unit 12 Delta/Delta and Delta/Wye Transformer Calculations Current Flow Part A Delta/Delta Transformers Delta Transformer Voltage Delta High-Leg Delta Line Currents Delta Phase Currents Delta Phase versus Line Current Delta Current Triangle Delta Transformer Balancing Delta Transformer Sizing Delta Panel Balancing Delta Panelboard and Conductor Sizing viii

6 Table of Contents Electrical Formulas with Sample Calculations Delta Neutral Current Delta Maximum Unbalanced Load Part B Delta/Wye Transformers Wye Transformer Voltage Wye Voltage Triangle Wye Transformers Current Wye Line Current Wye Phase Current Wye Phase Versus Line Current Wye Transformer Balancing Wye Transformer Sizing Wye Panel Balancing Wye Panelboard and Conductor Sizing Wye Neutral Current Wye Maximum Unbalanced Load Delta/Wye Example Delta Versus Wye Index ix