INM 9370-RD Rev 5
9
NOTE:
Whichever method is used, it is important to connect the screen/shield to ground
at one end of the cable only.
The cable shield is normally electrically isolated from the protective earth
ground, although the two may be deliberately interconnected in some
grounding arrangements. The cable shield wiring of the trunk and spur cables
should be connected to the local terminals marked with an ‘S’.
The following options are available to the user.
WARNING!
The following may involve changes to wiring in the Trunk Terminal
Assembly. No part of the Trunk Terminal Assembly may be worked
while the enclosure is powered, unless the environment is known to
be non-hazardous.
4.2.2.1 Single point of grounding at host; trunk & spur shields interconnected
Figure 4.1 - Option 1
In many installations, the preferred method of grounding is to ground the
fieldbus cable shields at one point only, normally at the fieldbus power supply.
In this case, the trunk and spur cable shields are connected to each other at
the Fieldbus Barrier and are not connected to ground in the field. For this
arrangement, connect the carrier shield ground wire (marked A) into Terminal 2.
Note: this is the default grounding method for factory-supplied 937x-FB enclosures.
IMPORTANT NOTE
937x-FB enclosures are factory-supplied with Option 1 grounding. If power is
applied locally, for example during commissioning, when the trunk cable shield
is NOT providing a ground connection, the spur cable shields must be grounded
according to Option 2.
When the trunk cable shield ground has been fully instated (or restored), the
grounding method should be returned to Option 1.
4.2.2.2 Trunk shield grounded at host; spur cable shields grounded at barrier
Figure 4.2 - Option 2
With this arrangement, the fieldbus trunk shield is separated from the spur cable
shields. It should be adopted if plant or local regulations require that the spur
cable shields be grounded at the Fieldbus Barrier. For this arrangement, connect the
carrier shield ground wire (marked A) into Terminal 3.
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