Modes of PROTECTION and SURGE

 A recent conversation with an engineer highlighted there was a confused relationship between modes of protection and modes of surge. This tutorial examines the meaning of modes of protection and how modes of surge come about. In conclusion, examples are given on the interaction of common-mode and differential mode surges with various protection arrangements.

Contents
1 Introduction 
2 Modes of PROTECTION
2.1 Common-mode and differential-mode protection
3 Surge modes 
3.1 Common-mode surge
3.2 Linear common-mode conversion 
3.3 Non-linear common-mode conversion -1
3.4 Non-linear common-mode conversion -2
4 Balanced and unbalanced differential surges
4.1 When a balanced surge meets voltage limiting
5 Summary