18 Rockwell Automation Publication 2080-UM001B-EN-E - November 2011
Chapter 4 Wire Your Controller
of surge suppression to protect and extend the operating life of the controllers
output contacts is required. Switching inductive loads without surge suppression
can significantly reduce the life expectancy of relay contacts. By adding a
suppression device directly across the coil of an inductive device, you prolong the
life of the output or relay contacts. You also reduce the effects of voltage
transients and electrical noise from radiating into adjacent systems.
The following diagram shows a typical PLC's output with a suppression device.
We recommend that you locate the suppression device as close as possible to the
load device.
If the outputs are DC, we recommend that you use an 1N4004 diode for surge
suppression, as shown below. For inductive DC load devices, a diode is suitable. A
1N4004 diode is acceptable for most applications. A surge suppressor can also be
used. See page 19
for recommended suppressors. As shown below with a typical
PLC's output, these surge suppression circuits connect directly across the load
device.
Suitable surge suppression methods for inductive AC load devices include a
varistor, an RC network, or an Allen-Bradley surge suppressor, all shown below.
These components must be appropriately rated to suppress the switching
+DC or L1
Suppression
Device
DC COM or L2
AC or DC
Outputs
Load
VAC/DC
Out 0
Out 1
Out 2
Out 3
Out 4
Out 5
Out
6
Out 7
COM
+24V DC
IN4004 Diode
Relay or Solid
State DC Outputs
24V DC common
VAC/DC
Out 0
Out 1
Out 2
Out 3
Out 4
Out 5
Out 6
Out 7
COM
(A surge suppressor
can also be used.)
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