Rockwell Automation Publication 1766-UM001O-EN-P - September 2021 35
Chapter 3 Wire Your Controller
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 an 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 a 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. Table 3 on page 36
for recommended suppressors.
As shown below, 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 transient characteristic of the particular inductive device. See
Recommended Surge Suppressors
on page 36 for recommended suppressors.
+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
(You can also use a surge
suppressor.)
Surge Suppression for Inductive AC Load Devices
Output device
Output device
Output device
Varistor
RC network
Surge
suppressor
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