Allen-Bradley 1756 Series, User Manual, Page: 68 / 136

68 Rockwell Automation Publication 1756-UM013B-EN-P - October 2019
Chapter 4 1756-OBV8S Output Module Features
Short Circuit Protection
Short Circuit Protection helps to prevent damage to the output that can result
when more current is present at the output than it can handle.
Table 18 describes what happens when a short circuit
condition is detected
on a
1756-OBV8S module.
Table 19 describes what happens when the short circuit condition is removed
from a 1756-OBV8S module and the data is set to safe state, that is, the off state.
You can monitor a point for the presence of short circuit faults via the diagnostics
page that is available in the Module Properties dialog box in Logix Designer
application.
For more information on the maximum current that you can apply to an output,
see the 1756 ControlLogix I/O Specifications Technical Data,
publication 1756-TD002 .
Table 18 - Short Circuit Protection - 1756-OBV8S Module
Output Behavior Tag Value Module Properties Points
Tab Diagnostic Value I/O Status Indicator
State
• Faults
• Turns off
One of the following:
• If the output point is
shorted to 24V DC, the
I.Ptxx.ShortCircuit
tag = 1.
• If the output point is
shorted to ground, no tags
are changed.
One of the following:
• If the output point was
shorted to 24V DC when
the short circuit condition
was detected, the Short
Circuit diagnostic = Yes.
• If the output point is
shorted to ground when
the short circuit condition
was detected, the Short
Circuit to Ground
diagnostic = Yes.
One of the following:
• Flashes red if the
output point is
shorted to 24V DC.
• Off if the output
point is shorted to
ground.
Table 19 - Short Circuit Protection - 1756-OBV8S Module
Output Behavior Tag Value Module Properties Points
Tab Diagnostic Value I/O Status Indicator
State
Restarts in its
commanded state One of the following:
• If the output point is
shorted to 24V DC, the
I.Ptxx.ShortCircuit
tag = 0.
• If the output point is
shorted to ground, no tags
are changed.
One of the following:
• If the output point was
shorted to 24V DC when
the short circuit condition
was detected, the Short
Circuit diagnostic = No.
IMPORTANT : You must
cycle power to the module
to reset the diagnostic.
• If the output point is
shorted to ground when
the short circuit condition
was detected, the Short
Circuit to Ground
diagnostic = No
Turns off if there is no
longer a load that is
connected to the
output.