Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 9)

5 Control circuits ..................................................................................................... 5-1
5.1 Utilization categories............................................................................................ 5-1
5.2 Control voltages ................................................................................................... 5-1
5.2.1 Alternating voltage .................................................................................................. 5-1
5.2.1.1 Control transformers for contactor controls ............................................................ 5-2
5.2.1.2 Frequencies < 50 Hz and > 60 Hz .......................................................................... 5-2
5.2.2 Direct voltage.......................................................................................................... 5-2
5.3 Switching contactors ........................................................................................... 5-3
5.3.1 Alternating current magnets.................................................................................... 5-3
5.3.1.1 Conventional alternating current magnets .............................................................. 5-3
5.3.1.2 Electronic coil control .............................................................................................. 5-3
5.3.2 Direct current drives................................................................................................ 5-4
5.3.2.1 “Conventional” ........................................................................................................ 5-4
5.3.2.2 Double winding coils ............................................................................................... 5-5
5.3.2.3 Electronic coil control .............................................................................................. 5-5
5.3.3 Electromagnetic compatibility and protective circuits.............................................. 5-5
5.3.3.1 Protective circuits in coil circuits ............................................................................. 5-5
5.3.4 Effect of long control lines....................................................................................... 5-7
5.3.4.1 Voltage drop ........................................................................................................... 5-7
5.3.4.2 Effect of the cable capacitance............................................................................... 5-8
5.3.5 Contact reliability .................................................................................................... 5-9
6 Considerations when building control systems and switchgear assemblies 6-1
6.1 Temperature rise................................................................................................... 6-1
6.1.1 Temperature rise limit values.................................................................................. 6-1
6.1.2 Laboratory test conditions and real practical environment...................................... 6-2
6.1.3 Verification of temperature-rise............................................................................... 6-3
6.1.4 Important aspects regarding device temperature rise; Recommendations............ 6-3
6.1.4.1 Rated current .......................................................................................................... 6-3
6.1.4.2 Thermal protective devices ..................................................................................... 6-4
6.1.4.3 Conductor cross sections ....................................................................................... 6-4
6.1.4.4 Conductor length .................................................................................................... 6-5
6.1.4.5 Tightening torques .................................................................................................. 6-5
6.1.4.6 Line ducting ............................................................................................................ 6-5
6.1.4.7 Operating frequency and harmonics....................................................................... 6-6
6.1.4.8 Mounting devices side-by-side ............................................................................... 6-6
6.1.4.9 Mounting position.................................................................................................... 6-6
6.1.5 Thermal imaging cameras ...................................................................................... 6-6
6.2 Short-circuit withstand capacity ......................................................................... 6-7
LVSAM-WP001A-EN-P - April 2009 0-9