Rockwell Automation Publication 440R-UM013F-EN-P - July 2021 25
Chapter 3 Power, Ground, and Wire
pulse tests are ignored as they are not used for short-circuit detection. These
terminals are intended for devices with high capacitance. For example, use
terminals 34 and 44 when connecting to the Enable input of the PowerFlex® 70
drive and the Safe Torque Off inputs of the PowerFlex and Kinetix® drives.
The pulse-tested outputs check for short circuits between the following:
•Each terminal.
• Each terminal and the 24V supply.
• Each terminal and 24V common. The load must be connected to the same
voltage reference as terminal A2.
The load must be connected to the same voltage reference as terminal A2. All
four OSSD outputs are short-circuit protected.
Figure 16 - OSSD Output Connections
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 surge
suppression to help protect and extend the operating life of the relays is
required. By adding a suppression device directly across the coil of an
inductive device, you prolong the life of the outputs. You also reduce the effects
of voltage transients and electrical noise from radiating into adjacent systems.
Figure 17
shows an output with a suppression device. We recommend that you
locate the suppression device as close as possible to the load device.
For outputs that use 24V DC, we recommend 1N4001 (50V reverse voltage) to
1N4007 (1000V reverse voltage) diodes for surge suppression for the OSSD
safety outputs (see Figure 17
). The diode must be connected as close as possible
to the load coil.
For outputs that use 120V AC or 240V AC, we recommend metal oxide
varistors.
Figure 17 - Surge Suppressors
34 44 14 24
A1
A2
K4K3K2K1
24V common
24V DC supply
DIS
K2K1
K2K1
V common V common
Metal Oxide Varistors
for VAC Supply
Diodes for
VDC Supplies
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