Rockwell Automation Publication 440R-RM003A-EN-P - July 2021 15
Chapter 2 CU3 Control Unit
Output Load Capability The following table compares the output load capabilities of the CU3 control
unit and MSR55P safety relay. The output switching capability of the two relays
is similar. For AC loads, the MSR55P safety relay is derated when operating at
higher ambient temperatures.
The MSR55P safety relay has a higher DC current rating than the CU3 control
unit.
Feedback Monitoring As shown in Figure 6, both the CU3 control unit and the MSR55P safety relay
are able to monitor their respective output devices with automatic/manual
monitoring on terminals X1 and X2.
Automatic monitoring is accomplished by connecting the monitored contacts
in series to X1 and X2. Manual reset is accomplished by adding a momentary
normally open push button in series with the monitored contacts.
Figure 6 - Automatic and Manual Reset
Load Description CU3 MSR55P
AC-15 B300
5 A @ 250V AC
5 A @ 120V AC
5 A @ 250V AC @ 40 °C (104 °F)
2 A @ 250V AC @ 60 °C (140 °F)
DC 3 A @ 24V DC 4 A @ 24V DC
Upon manual reset, the MSR55P displays a fault code 4.
L1 L2 L3
M
K2
K2
X1
X2
3~
L1 L2 L3
M
K2
K2
X1
X2
3~
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