Publication 1764-UM001B-EN-P - April 2002
3-4 Wiring Your Controller
Using Surge Suppressors
Inductive load devices, such as motor starters and solenoids, require
the use of some type of surge suppression to protect and extend the
operating life of the controller’s output contacts. 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 an 1N4004 diode
for surge suppression, as shown below.
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 the table on page 3-6 for
recommended suppressors.
VAC/D
Out 0
Out 1
Out 2
Out 3
Out 4
Out 5
Out 6
Out 7
COM
+dc or L1
Suppression
Device
dc COM or L2
ac or dc
Outputs
VAC/D
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
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