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Cabling
The use of industrial grade, suitably shielded field cable is recommended. The best practices
shown that, screened 3 cores (plus screen 90% coverage), suitably mechanically protected
copper cable with a suitable explosion-proof gland, or ¾" NPT steel conduit, depending on the
distance between signal received or control panel and detector 0.5 to 2.5 mm2 (20 to 13
AWG) conductors can give better results. Ensure the cable gland is installed correctly and fully
tightened.
Cable and Earth/Ground regimes
Effective Earth/Ground bonding is important to ensure good EMC and RFI immunity. The
following diagrams show examples of how to earth/ground bond the cable at enclosures. The
same principles apply to conduit installations. These bonding techniques provide good
RFI/EMC performance. Earth/ground loops must be avoided to prevent the risk of false signal
variation.
Diagram 5: Grounding
The Earth Screen of the field cable should be "tied to Earth" or connected to Ground at one
point only. It is common practise to adopt a STAR EARTH connection regime where all
instrumentation Screens are connected at one common point. The Screen at the other end of
the cable should be "parked" or terminated into a blank terminal.
11
PRS-UM-PC3-EN-Rev.04-06.2020
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