Rockwell Automation 1786-series ControlNet Coax Media Planning and Installation Guide User Manual
Page 37
Publication CNET-IN002B-EN-P - June 2010
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Plan a ControlNet Coax Media System Chapter 2
Surge Suppression
Transient electromagnetic interference (EMI) can be generated whenever
inductive loads, such as relays, solenoids, motor starters, or motors are
operated by ‘hard contacts’. Push button or selector switches are examples of
hard contacts. These wiring guidelines assume you guard your system against
the effects of transient EMI by using surge-suppressors on these devices to
suppress transient EMI at its source.
Inductive loads switched by solid-state output devices alone do not require
. However, inductive loads of AC output modules that are in
series or parallel with hard contacts require surge-suppression to protect the
module output circuits as well as to suppress transient EMI.
Ferrite Beads
Ferrite beads provide additional suppression of EMI. Each tap has three beads
integral to the tap drop cable. In rare instances where EMI is extremely high, it
may be necessary to install additional ferrite beads on the trunk cable.
When necessary, secure the ferrite beads with heat-shrink tubing or tie-wraps.
When using tie-wraps, be careful not to deform or crush the coax cable. Do
not loop the coax cable through the ferrite bead as this will exceed the
minimum bend radius of the cable and cause permanent damage to the cable.