Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 161)

With momentary contact control the line length is halved. Graphic presentation for the control
voltages 110 V and 230 V see
Fig. 5.3-8 .
As the cable capacitance is very much dependent on the type of cable, it is recommended in
case of doubt to obtain the specific value from the manufacturer or to measure it.
10
100
1000
1 10 100 S [VA]
l [m]
110V
230V
Fig. 5.3-8
Permissible line length in accordance with the above conditions for maintained contact control at control
voltages of 110 V and 230 V at 50 Hz
l Line
length
S Apparent power (holding power) of the contactor
If there are problems with respect to the permissible line length because of the line capacitance
the following measures are possible in accordance with above discussion:
ƒ Application of an additional load (resistor parallel to contactor coil)
ƒ Use of a larger contactor with bigger holding power
ƒ Use of a lower control voltage
ƒ Use of direct voltage
5.3.5 Contact reliability
Electronic devices and circuits as commonly used in industrial applications, for example in PLC
control devices and safety relays put high demands on the functional reliability of the controlling
contacts, whether auxiliary switches of power switchgear or for example contacts of control
units, sensors, function relays etc. The voltage to be switched is usually 24 V or even lower and
the switching currents remain in the low mA range. Contacts connected in series (for example to
safety relays) are frequently de-energized when they close and open, so that a switching
operation under electrical load never takes place.
LVSAM-WP001A-EN-P - April 2009 5-9