ITU-T Rec. K.11 (1991) – PRINCIPLES OF PROTECTION AGAINST OVERVOLTAGES AND OVERCURRENTS
FOREWORD
Introduction
1 General considerations
    1.1 Origin of dangerous overvoltages and overcurrents
        1.1.1 Direct lightning strikes
        1.1.2 Lightning strikes nearby
        1.1.3 Induction from fault currents in power lines including electric traction systems
        1.1.4 Contacts with power lines
        1.1.5 Rise of earth potential
    1.2 Methods of protection
    1.3 Types of protective devices
        1.3.1 Air-gap protectors with carbon or metallic electrodes
        1.3.2 Gas discharge tubes
        1.3.3 Semi-conductor protective devices
        1.3.4 Fuses
        1.3.5 Heat coils
        1.3.6 Self-restoring current-limiting devices
        1.3.7 Fusible links
    1.4 Residual effects
        1.4.1 Residual overvoltages
        1.4.2 Transverse voltages
        1.4.3 Effect on normal circuit operation - Coordinated design
        1.4.4 Modifying effects
        1.4.5 Coordination of primary and secondary protection
        1.4.6 Temperature rise
        1.4.7 Circuit availability
        1.4.8 Fault liability
    1.5 Assessment of risk
        1.5.1 The performance of a telecommunications system
        1.5.2 The environment
        1.5.3 Fault records
    1.6 Decision on protection
2 Protection of lines
    2.1 Protective measures external to the conductors themselves
    2.2 Special cables
    2.3 Use of protective devices
    2.4 Installation of protective devices
    2.5 Planning of works
    2.6 Recommended policy
3 Protection of exchange and transmission equipment
    3.1 Need for protection external to the equipment
    3.2 Need for equipment to have a minimum level of electrical robustness
    3.3 Effect of switching conditions
4 Protection of subscribers' terminal equipment
    4.1 Degree of exposure
    4.2 Dielectric strength
    4.3 Use of protectors
    4.4 Common bonding
    4.5 National regulations
    4.6 High cost of maintenance of subscribers' installations
References