ITU-T Rec. K.20 (1991) – RESISTIBILITY OF TELECOMMUNICATION SWITCHING EQUIPMENT TO OVERVOLTAGES AND OVERCURRENTS
FOREWORD
1 General
2 Scope
3 Overvoltages and overcurrent conditions
4 Levels of resistibility
5 Exchange equipment boundary
6 Test conditions
7 Permitted malfunction or damage
8 Tests
    8.1 General
    8.2 Unexposed environment
    8.3 Exposed environment
ANNEX A – Explanations which illustrate test conditions
A.1 Lightning surges
A.2 Power induction
A.3 Power contacts
APPENDIX I – Over-voltages occurring simultaneously on a number of telephone lines
I.1 Type test
I.2 Effects of lightning
I.3 Lightning simulation
I.4 Modified secondary protection
I.5 Conclusion