44 Rockwell Automation Publication 2080-UM002N-EN-E - November 2022
Chapter 4 Wire Your Controller
Use Surge Suppressors Because of the potentially high current surges that occur when switching inductive load
devices, such as motor starters and solenoids, the use of some type 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.
Figure 3
shows an output with a suppression device. We recommend that you locate the
suppression device as close as possible to the load device.
Figure 3 - Output with Suppression Device
If the outputs are DC, we recommend that you use an 1N4004 diode for surge suppression, as
shown in Figure 4. 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 Recommended
Surge Suppressors on page 45. These surge suppression circuits connect directly across the
load device.
Figure 4 - DC Outputs with Surge Suppression
Suitable surge suppression methods for inductive AC load devices include a varistor, an RC
network, or an Allen-Bradley surge suppressor, shown in Figure 5
. These components must be
appropriately rated to suppress the switching transient characteristic of the particular
inductive device. See Recommended Surge Suppressors
on page 45 for recommended
suppressors.
Wire Requirements
Wire Size
Type Min Max
Micro830/
Micro850/
Micro870
Controllers
Solid
0.2 mm
2
(24 AWG) 2.5 mm
2
(12 AWG)
rated @ 90 °C (194 °F)
insulation max
Stranded
0.2 mm
2
(24 AWG) 2.5 mm
2
(12 AWG)
+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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