PC3000 Complete Installation guide iss 12 - Elektro-Trading

Appendix A
Enclosure of live parts
Metal parts of certain types of equipment can become electrically “live” under
normal operating conditions.
Unless clearly intended to be panel mounted and accessible during normal operation,
all units should be installed inside a suitable earthed metal enclosure to prevent live
parts being accessible to human hands and metal tools.
Wiring
It is important to connect all equipment correctly in accordance with the installation
data provided for each type of unit.
Most connections to equipment require correct polarity to be maintained and due
attention must be given to ensure this.
Unlabelled terminals must not be used as “tie points” for other wires.
Conductors should be commensurate with voltage and current ratings of the units,
and should conform to appropriate standards of good practice and local codes and
regulations.
Screened cables
In installations where high electrical noise cannot be avoided, twisted pairs or
screened cables are recommended as below:
Thermocouple Inputs Use screened compensating cable
Resistance Thermometers Use screened cable
Logic Inputs/Outputs Use screened twisted conductors
Analogue Control Outputs Use screened twisted pairs
Logic Control Outputs Use twisted pairs
Retransmission Signals Use twisted pairs
Relay Outputs Use standard cable
Where screened twisted pairs are used the screen must be earthed at one end only,
preferably at the instrument.
Routing of wiring
Care should be taken to ensure maximum separation between low current or signal
wiring and power wiring.
Control wiring refers to those connections to the input of the PC3000 system,
analogue or logic outputs, digital inputs, remote setpoint inputs and relays switching
control signals .
Power wiring refers to those connections to relay or triac AC supplies, and wiring
associated with external devices such as contactors, alarm relays or motor speed
drives etc.
This requires that the mechanical design must take into account all the different
items to be included and the type of wiring involved. The design layout should
App. A-2
PC3000 Installation Guide