Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 8)

4.1.2.2 Protection in continuous duty and at transient loads .............................................. 4-4
4.1.2.3 Overload and overtemperature protection by measurement of current and
measurement of temperature ................................................................................. 4-7
4.1.2.4 Protective functions ................................................................................................ 4-8
4.1.2.4.1 Protection during starting, monitoring of starting time, start interlocking .............. 4-10
4.1.2.4.2 Asymmetry protection ........................................................................................... 4-10
4.1.2.4.3 Phase failure protection ........................................................................................ 4-11
4.1.2.4.4 Stalling protection ................................................................................................. 4-13
4.1.2.4.5 Underload protection ............................................................................................ 4-14
4.1.2.4.6 Automatic switching-over during start-up.............................................................. 4-14
4.1.2.4.7 Ground fault protection ......................................................................................... 4-14
4.1.2.5 Display, warning and control functions ................................................................. 4-15
4.1.3 Protection against high overcurrents, short-circuit protection ............................... 4-16
4.1.3.1 Definition and characteristic of a short-circuit ....................................................... 4-16
4.1.3.2 Effects of and dangers in case of short-circuits .................................................... 4-17
4.1.3.3 Protection requirements........................................................................................ 4-18
4.1.3.3.1 Switching capacity ................................................................................................ 4-18
4.1.3.3.2 Current limitation................................................................................................... 4-18
4.1.3.3.3 Selectivity.............................................................................................................. 4-19
4.1.3.3.4 Short-circuit coordination ...................................................................................... 4-22
4.2 Protective devices .............................................................................................. 4-22
4.2.1 Fuses .................................................................................................................... 4-22
4.2.1.1 Principle of operation ............................................................................................ 4-22
4.2.1.1.1 Current limitation................................................................................................... 4-23
4.2.1.1.2 Breaking capacity ................................................................................................. 4-23
4.2.1.2 Standards and utilization categories ..................................................................... 4-23
4.2.1.2.1 Classification and time/current zones ................................................................... 4-24
4.2.1.3 Designs................................................................................................................. 4-25
4.2.2 Circuit breakers..................................................................................................... 4-26
4.2.2.1 Principle of operation and design ......................................................................... 4-26
4.2.2.2 Standards, functions and utilization categories .................................................... 4-26
4.2.2.2.1 Standards ............................................................................................................. 4-26
4.2.2.2.2 Functions and utilization categories...................................................................... 4-26
4.2.2.3 Design of a circuit breaker .................................................................................... 4-28
4.2.2.3.1 Thermal overcurrent releases ............................................................................... 4-28
4.2.2.3.2 Electromagnetic overcurrent releases .................................................................. 4-29
4.2.2.3.3 Main contact system and switching capacity ........................................................ 4-29
4.2.2.4 Application of circuit breakers ............................................................................... 4-32
4.2.2.4.1 Application as circuit breaker ................................................................................ 4-32
4.2.2.5 Installation of circuit breakers, safety clearances ................................................. 4-34
4.2.3 Miniature Circuit Breakers MCB ........................................................................... 4-35
4.2.3.1 Principle of operation and design ......................................................................... 4-35
4.2.3.2 Standards, tripping characteristics and rated switching capacity.......................... 4-35
4.2.3.3 Installation of Miniature Circuit Breakers, safety clearances ................................ 4-36
4.2.4 Motor protection relays (overload relays) ............................................................. 4-36
4.2.4.1 Thermal motor protection relays ........................................................................... 4-36
4.2.4.2 Electronic motor protection relays ........................................................................ 4-40
4.2.4.2.1 Principle of operation ............................................................................................ 4-41
4.2.4.3 Thermistor protection relays ................................................................................. 4-42
4.2.4.3.1 Relays for PTC sensors ........................................................................................ 4-42
4.2.4.3.2 Relays for NTC sensors........................................................................................ 4-43
4.2.4.3.3 Metal resistance sensors ...................................................................................... 4-43
LVSAM-WP001A-EN-P - April 2009 0-8