Electrical Contacts Principles and Applications

edited by Paul G» Slade

Cutler-Hammer Horseheads, New York

@ Taylor &. Francis Taylor & Francis Group Boca Raton London New York

CRC is an imprint of the Taylor & Francis Croup, an informa business

Contents

Preface Hi Contributors xiii Introduction xv

Part One CONTACT INTERFACE CONDUCTION

1 Electrical Contact Resistance: Fundamental Principles 1 Roland S. Timsit

1.1 Introduction 1 1.2 Electrical Constriction Resistance 2 1.3 The Effect of Surface Films on Constriction and Contact Resistance 15 1.4 Temperature of an Electrically Heated a-Spot 45 1.5 Mechanics of a-Spot Formation 58 1.6 Breakdown of Classical Electrical Contact Theory 72 1.7 Summary 75

Appendix l.A 76 Appendix l.B 79 Appendix l.C 80 References 83

vi

Introduction to Contact Tarnishing and Corrosion 89 Paul G. Slade

2.1 Introduction 89 2.2 Corrosion Rates 90 2.3 Corrosive Gases 92 2.4 Types of Corrosion 93 2.5 Gas Concentrations in the Atmosphere 100 2.6 Measurements 101 2.7 Mixed Flow Gas Laboratory Testing 105 2.8 Electronic Connectors 106 2.9 Power Connectors 108 2.10 Other Considerations 108

References 110

Contact Corrosion 113 William H. Abbott

3.1 Introduction 113 3.2 The Field Environments for Electrical Contacts 117 3.3 Laboratory Accelerated Testing 132 3.4 Corrosion Inhibition—Lubrication 150

References 153

Part Two NONARCING CONTACTS

4 Power Connections 155 Milenko Braunovic

4.1 Introduction 155 4.2 Types of Power Connectors 157 4.3 Properties of Conductor and Connector Materials 158 4.4 Parameters Affecting Performance of Power Connector 169 4.5 Palliative Measures 219 4.6 Accelerated Current-Cycling Tests (Standards) 252 4.7 Shape-Memory Alloys (SMA) 256

References 270

5 Low Power Commercial Wiring, Automotive, and Appliance Connections 279 Anthony Lee

5.1 Introduction 279 5.2 Connectors 281 5.3 Contact Terminals 288 5.4 Connector Contact Degradation 297 5.5 Summary 305

References 306

Contents vii

6.1 6.2 6.3 6.4

Introduction Sliding Wear Fretting Lubrication References

Tribology of Electronic Connectors: Contact Sliding Wear, Fretting, and Lubrication 309 Morton Antler

309 309 332 364 394

Materials, Coatings, and Platings 403 Morton Antler

7.1 Introduction 403 7.2 Metallic Finishes 404 7.3 Properties Related to Porosity 409 7.4 Metallurgical and Structural Properties 414 7.5 Physical and Mechanical Properties 423

References 430

Part Three THE ELECTRIC ARC AND SWITCHING DEVICE TECHNOLOGY

8 The Arc and Interruption 433 Paul G. Slade

8.1 Introduction 433 8.2 The Fourth State of Matter 433 8.3 Establishing an Arc 438 8.4 Formation of the Electric Arc 451 8.5 The Arc in Air at Atmospheric Pressure 454 8.6 The Arc in Vacuum 469 8.7 Arc Interruption 473

References 483

9 The Consequences of Arcing 487 Paul G. Slade

9.1 Introduction 487 9.2 Arcing Time 487 9.3 Arc Erosion of Electric Contacts 496 9.4 Blow-Off Force 508 9.5 Contact Welding 513 9.6 Changes in the Contact Surface as a Result of Arcing 520

References 530

10 Reed Switches 535 Kunio Hinohara

10.1 Principles and Design of the Reed Switch 535

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10.2 Recommended Contact Plating 549 10.3 Contact Surface Degradation and Countermeasures 552 10.4 Applications of Reed Switches 564

References 571

11 Low Current Switching 573 John W. McBride

11.1 Introduction and Device Classification 573 11.2 Device Types 574 11.3 Design Parameters for Static Switching Contacts 584 11.4 Mechanical Design Parameters 586 11.5 Electrical Characteristics of Low Current Switching Devices at

Opening 603 11.6 Electrical Characteristics of Low Current Switching Devices at

Closure 614 11.7 Summary 621 11.8 Afterword 623

References 624

12 Medium to High Current Switching 627 Manfred Lindmayer

12.1 General Aspects of Switching in Air 627 12.2 Contacts for Switching in Air 631 12.3 Low-Voltage Contactors 632 12.4 Low-Voltage Circuit-Breakers and Miniature Circuit-Breakers 648 12.5 Vacuum Interrupters 663

References 675

Part Four ARCING CONTACT MATERIALS

13 Arcing Contact Materials 681 Gerald J. Witter

13.1 Introduction 681 13.2 Silver Metal Oxides 684 13.3 Silver Refractory Metals 703 13.4 Vacuum Interrupter Materials 732 13.5 Other Special Applications for Refractory Metals 732 13.6 Non-Noble Silver Alloys 733 13.7 Silver-Nickel Contact Materials 735 13.8 Silver Alloys and Noble Metals 737 13.9 Silver Graphite Contact Materials 741 13.10 Conclusion 742

References 744

Contents

14 Contact Design and Attachment Gerald J. Witter and Guenther Horn

14.1 Introduction 14.2 Staked Contact Assembly Designs 14.3 Welded Contact Assembly Designs 14.4 Brazed Contact Assembly Designs 14.5 Clad Metals, Inlay, and Edge Lay 14.6 Non-Arcing Separable Contact Alloys

References

15 Material Performance Evaluation and Test Methods Werner Rieder

15.1 Purpose 15.2 The Problem of Contact Evaluation 15.3 Test Methods 15.4 Test Realization

References

16 Arc Interactions with Contaminants Werner Rieder and Gerald J. Witter

16.1 Introduction 16.2 Organic Contamination and Activation 16.3 Mineral Particulate Contamination of Arcing Contacts 16.4 Silicone Contamination of Arcing Contacts 16.5 Lubricants with Refractory Fillers 16.6 Oxidation of Contact Materials 16.7 Resistance Effects from Long Arcs

References

Part Five SLIDING ELECTRICAL CONTACTS

17 Sliding Electrical Contacts (Graphitic Type Lubrication) Erie I. Shobert II

17.1 Introduction 17.2 Mechanical Aspects 17.3 Chemical Aspects 17.4 Electrical Effects 17.5 Thermal Effects 17.6 Brush Wear 17.7 Brush Materials and Abrasion 17.8 Summary

References

Contents

Illustrative Modern Brush Applications 873 Wilferd E. Yohe and William A. Nystrom

18.2 Introduction 873 18.2 Brush Materials 874 18.3 Brush Applications 876

Sliding Contacts for Instrumentation and Control 885 E. W. Glossbrenner

19.1 Definitions: Sliding Versus Static and Wiping Contacts 885 19.2 Macro Sliding Contacts 887 19.3 Micro Sliding Contact: Mechanical Aspects 901 19.4 Micro Sliding Contact: Electrical Aspects 911 19.5 Environment and Film Formation 915 19.6 Lubrication 922 19.7 Contact Parameters and Sliding-Contact Assemblies 927 19.8 Friction and Wear Performance 931 19.9 Inferences from Test and Examination of Performing Slip Ring

and Brush Contacts 936 19.10 Summary 938

References 939

Metal Fiber Brushes 943 Doris Kuhlmann- Wilsdorf

20.1 Introduction 943 20.2 Elastic Versus Plastic Contact Spots 945 20.3 Solving the Brush Wear Problem via Elastic Contact Spots 947 20.4 Basic Equations Governing Electrical Brush Resistance 951 20.5 Surface Films, Friction, and Materials Properties 953 20.6 Factors Affecting Performance of Fiber Brushes 957 20.7 Fallacious Apparent Speed of Fiber Brushes Based on the

"Softening Voltage" 967 20.8 Speed-Current-Density Limits Based on Flash Temperatures

and Wear 971 20.9 Fiber-Brush Cooling and Cooling by Means of Fiber Brushes 982 20.10 Optimizing Brush Performance 992 20.11 Advancing Towards Widespread Technological Fiber-Brush

Application 998 20.12 Potential Application of Fiber Brushes and Outlook for the Future 1009

Appendix 1010 Symbols 1012 References 1015

Contents XI

Part Six CONTACT DATA

21 Useful Electric Contact Information 1019 Paul G. Slade

21.1 Introduction 1019 21.2 Notes to the Tables 1019

References 1021

Author Index 1041 Subject Index 1055