Rockwell Automation 1747-L5xx SLC 500 Modular Hardware Style User Manual - Manual (Page 48)

Publication 1747-UM011G-EN-P - June 2008
48 Selecting Your Hardware Components
when such loads are connected as output devices or when connected
to the same supply line that powers the controller.
Lack of surge suppression on inductive loads may contribute to
processor faults and sporadic operation. RAM can be corrupted (lost)
and I/O modules may appear to be faulty or reset themselves.
For extremely noisy environments, use a memory module and
program it for auto-loading on processor fault or power cycle for
quick recovery.
Selecting Surge Suppressors
Most output modules have built-in surge suppression to reduce the
effects of high voltage transients. However, you should use an
additional suppression device if an output module is being used to
control an inductive device such as:
• relays.
• motor starters.
• solenoids.
• motors.
Additional suppression is especially important if your inductive device
is in series with or parallel to a hard contact such as:
• push buttons.
• selector switches.
By adding a suppression device directly across the coil of an inductive
device, you reduce the effects of voltage transients caused by
interrupting the current to that inductive device and prolong the life of
the switch contacts. You also prevent electrical noise from radiating
into system wiring. The diagram below shows an output module with
a suppression device.