66 Rockwell Automation Publication 440R-UM013E-EN-P - March 2017
Chapter 11 Troubleshooting
Verify Grounding at the Power Supply
IEC 60204-1 and NFPA79 require that the 24V is supplied by a PELV-rated
power supply. The 24V common must be connected to protective earth, as
shown in Figure 59
. The protective ground connection must only be in one
location and is often best when closest to the power supply.
Ground loops and noise transients on the ground can cause the GSR relays to
go into a fault state. This state is hard to capture. One method is to remove the
protective grounding connection between machine ground and the 24V
common temporarily. Then, wait to see if the fault does not occur (wait time
varies). If the fault occurs, then the grounding scheme must be investigated
further.
Figure 59 - 24V Common to Protective Earth Connection
IEC 60204-1 edition 5.1 (Section 6.1) allows a SELV supply to be used when a
PELV is not practicable due to physical or operational conditions. NFPA79
does not allow the use of a SELV supply. If you are meeting only IEC 60204-1,
you can install a separate SELV supply for your safety system and leave it
ungrounded (no protective ground).
Check Safety Device Inputs
(Step 3)
This step only applies to CI, DI, DIS, and SI safety relays. Each safety relay has
a status indicator for its inputs.
+ + - -
24V DC
L N
PELV
Power
Supply
AC
Power
Supply
+24V DC
+24V Common
A2 13
S11 S12A1
GSR Safety Relay
Temporarily remove the protective ground
connection for troubleshooting. Reconnect
ground after completing.
Table 13 - Input Indicator
IN, IN1, and IN2 Indicator Status Action
Green Both channels are closed Go to Check the Single Wire Safety
Circuit (Step 4) on page 74.
Off One or both input channels are open Continue with this section.
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