Specifications

2–26 Selecting Your Hardware Components
Publication 1747-6.2
Selecting Contact Protection
Inductive load devices such as motor starters and solenoids may
require the use of some type of surge suppression to protect the
controller output contacts. Switching inductive loads without surge
suppression can significantly reduce the lifetime of relay contacts.
The figure below shows the use of surge suppression devices.
Output Device
Output Device
Varistor
Output Device Output Device
RC Network
Surge
Suppressor
Diode (A surge suppressor can also be used.)
—
+
Surge Suppression for Inductive DC Load Devices
Surge Suppression for Inductive AC Load Devices
Contact protection methods for inductive AC and DC output devices.
These surge suppression circuits connect directly across the load
device. This reduces arcing of the output contacts. (High transient
can cause arcing that occurs when switching off an inductive device.)
Suitable surge suppression methods for inductive AC load devices
include a varistor, an RC network, or an Allen-Bradley surge
suppressor. These components must be appropriately rated to
suppress the switching transient characteristic of the particular
inductive device.
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 table on page 2–25.
We recommend that you locate the suppression device as close as
possible to the load device.