User guide

Wiring and Cabling
138
890 USE 108 00 August 2001
Guarding Against EMI/RFI
Overview of EMI/
RFI Protection
As part of your installation procedure, take care to protect the Compact Controller
from extraneous electrical noise interference caused by system wiring. The single
best precaution that can be taken against radiated electrical noise is mounting the
system inside a metal cabinet that is grounded to the building’s structural metal.
Even office environments can benefit from this precaution.
General
Precautions
Against EMI/RFI
In all installations, the following precautions should be taken:
Tighten backplane and module mounting screws securely
Run ac, dc, and analog wiring in separate cable trays or conduit
Always shield analog RTD or Thermocouple wiring
Cabinet
Installations
The following precautions should be taken when installing a Compact in a NEMA
cabinet:
Do not mix ac power and signal-level wiring in a cable trays or conduit
Run ac and dc supply wiring separately, preferably in channels on opposite sides
of the cabinet; if cables must cross each other, cross them at right angles
Shield all analog field wiring, particularly if it is run in the same cable or channel
as 24 Vdc field wiring
Place suppression devices-i.e., diodes, capacitors, resistors-across relays,
solenoids, and other magnetic-field generating components
Shield magnetic-field generating components from the controller and I/O
modules with a metal plate-a bare metal contact between the plate and the
cabinet is required
Ideally, magnetic-field generating components should be mounted in separate
cabinets
Fluorescent lights generate electrical noise-do not use them inside a working
cabinet