Instruction manual

8
INM9380-RD-1
May 2012
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.
Note: After configuring the required grounding option, tighten all screw terminals to a
recommended torque of 0.6 Nm.
4.2.3 Permitted assembly combinations
The maximum number of redundant intrinsically safe spurs that can be supported on a trunk
segment is 12. The permitted assembly combinations are shown in Figure 4.3.
Note that a fieldbus terminator (9378-FT) must be fitted (see Section 4.4) to the last/
furthest assembly on the segment. See also Figure 4.6.
4.3 Trunk connections
Each Trunk Termination Assembly (TTA) is provided with two access holes and grommets
for trunk wiring; one for the incoming trunk and another for onward linking to an
additional assembly, if necessary.
WARNING!
No part of the Trunk Terminal Assembly may be worked while
the enclosure is powered, unless the environment is known to
be non-hazardous.
4.3.1 Trunk Terminal Assembly
The trunk cables are terminated in the Trunk Terminal Assembly (TTA). This is a sub-
enclosure with a protective lid, secured with a single screw. This assembly, together
with its warning label, is intended to deter a user from working on the trunk connections
without isolating trunk power. See Figure 4.6.
Trunk cables enter the TTA through grommets and these must be cleanly cut with a
sharp knife to ensure the IP30 rating is maintained (see Section 4.3.2). The grommet is
supplied with the cone facing into the TTA, but the user is free to reverse this and allow
the cone to extend outwards.
Terminals are provided to allow a variety of wiring arrangements, according to the
particular requirements of the installation:
– “Trunk In” cable only
– “Trunk In” and “Trunk Out” cables
– Active and spare “Trunk In” cables
– Active and spare “Trunk In” cables with overall cable shield
– Active and spare “Trunk In” cables and “Trunk Out” cable
CAUTION
The ‘+’ and ‘–’ wires of a ‘spare’ trunk in cable must be connected only to
terminals marked ‘NC’. This ensures that the spare cable is not electrically
connected in parallel with the ‘active’ trunk in or trunk out cables. The cable
shield of the spare cable should be connected to an ‘S’ terminal.
All ‘spare’ trunk-in connections (‘+’, ‘–’ and shield) must be firmly grounded
at the host.
4.3.2 Trunk cable wiring
Connect the trunk cable(s) in the following way.
a) Loosen the captive screw of the transparent protective cover on the TTA. Slide out the
cover and move it to one side to obtain access.