Rockwell Automation T8094 8000 Series TMR System Safety Manual - Manual (Page 72)

SAFETY MANUAL
D oc N umber T8094
I ssue 27 – June 2013
Page 51 of 103
3.13.3.2 Preparing and Earthing the Controller Chassis
Install module blanking panels (shields) on all empty module positions in the Trusted TM
T8100 controller chassis. This will reduce the strength of unwanted electromagnetic
emissions during system commissioning and maintenance work when the enclosure
doors are open.
The chassis must be connected to the EMC enclosure using a cable no smaller than
4mm
2 area and no longer than 200 mm.
3.13.3.3 Enclosure Internal Wiring
Cable pigtails which provide a functional earth connection between Trusted TM modules
and their field termination assemblies must be connected directly to the controller
chassis at the module end, and to the EMC enclosure at the field termination assembly
end.
3.13.3.4 Cable Entries
Each cable which passes through the boundary of the enclosure (the boundary means
the sides, floor and top) must be shielded (screened) or pass through an EMC filter
unit bonded directly to the EMC enclosure. This includes AC mains power cables, field
wiring, and serial and Ethernet communications cables.
Cable shields must remain intact up to the boundary of the enclosure, and must be
connected to earth at the boundary of the enclosure:
• Shielded cables must use a gland or a shielded cable connector at the location
where they enter the enclosure. The gland or shielded connector chosen must
provide the shortest possible path between the cable shield and the enclosure
wall.
• Do not use pigtails to make earth connections for cable shields. These can act
like miniature antennas and make EMC emissions worse.
3.13.4 System Power Requirements
The system’s power supplies and distribution, if incorrectly designed, present a
potential common cause failure. It is therefore necessary to:
• Establish the power philosophy, specific earthing philosophy
4 , required
voltage and power requirements, and the separation requirements where
items of equipment are separately supplied, e.g. system internal supplies and
field loop supplies.
• Define the architecture of the Power Supply Units (PSU), e.g. 100%
redundancy, dual N+1 redundancy, etc. and ensure that each power source
is of adequate capability.
• Ensure that the PSUs are compatible with the power feeds provided.
Alternatively, measures should be implemented to ensure that the PSU
power feeds remain within the PSU specifications.
• Define the power distribution requirements, together with the protective
philosophy for each distribution, e.g. current limited at source or protective
devices. Where protective devices are used, it is important to establish that
4
Rockwell Automation recommends that the negative side of the field supply be connected to earth
(ground). This will avoid possible fail danger conditions that can be caused by some earth fault monitors
used with floating power supplies.