MAN0923_Issue 3_04/15
Touchpoint Pro
Operating Instructions
49
•
Instrument Earth is preferred to connect the cable screen
•
Risk is that screen is connected at both ends = earth loops
4. Electrical Installation
Incoming
Client
Earth
Three Core Cable with Screen Earthed at Contoller
Junction
Box
Sensor
P
Figure 4.3 Screened cable, metal junction box and/or sensor
•
Instrument Earth is preferred to connect the cable screen
•
Care must be taken to isolate the screen at the junction box, e.g. terminate it in a spare terminal
•
The metal sensor / junction box must be connected to Protective Earth
•
Risk is that screen is connected at both ends = earth loops
Incoming
Client
Earth
Three Core Cable with Screen and Armour with Screen Earthed at Controller
and Armour Earthed in Field
Junction
Box
Sensor
Armour
Screen
P
Figure 4.4 Screened cable with armour (wire or braid) with plastic junction box and plastic sensor
•
The armour must be connected to Protective Earth at the sensor, and the screen should be connected to
the enclosure’s common earth (ground) rail.
•
Care must be exercised to prevent contact between cable armour and cable screen, and between
cable armour and the enclosure in order to prevent ground loops occurring.
