Rockwell Automation 1747-L40 SLC 500 Fixed Hardware Style - Manual (Page 33)

Chapter 1
Selecting Your Hardware Components
1–14
Selecting Surge Suppressors
Most output modules have built–in surge suppression to reduce the effects of
high voltage transients. However, we recommend that you 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:
•
pushbuttons
•
selector switches
By adding a suppression device directly across the coil of an inductive
device, you will reduce the effects of voltage transients caused by
interrupting the current to that inductive device and prolong the life of the
switch contacts. The diagram below shows an output module with a
suppression device.
OUT 5
OUT 6
OUT 7
OUT 2
VAC/VDC
OUT 0
OUT 1
OUT 3
COM
+ DC or L1
OUT 4
Snubber
AC or DC
Output Module
DC COM or L2
If you connect an SLC 500 controller triac output to control an inductive
load, we recommend that you use varistors to suppress noise. Choose a
varistor that is appropriate for the application. The surge suppression we
recommend for triac outputs when switching 120 VAC inductive loads is
Harris MOV, part number V220 MA2A. For a 509 motor starter, use a
599–K04 or 599–KA04 series C or later MOV with triac outputs.
Consult the varistor manufacturer’s data sheet when selecting a varistor for
your application.
!
ATTENTION: Damage could occur to SLC 500 triac outputs if
you use suppressors having RC networks. Allen–Bradley AC
surge suppressors not recommended for use with triacs include
Catalog Numbers 199–FSMA1, 199–FSMA2, 1401–N10, and
700–N24.