Rockwell Automation Publication 440R-UM013F-EN-P - July 2021 57
Chapter 11 Troubleshooting
Figure 58 - Measure Power Supply Voltage
If the voltage is not within the acceptable range, verify that the power supply,
wiring, circuit breakers, and/or fuses are functioning properly.
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 safety
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
OUT
PWR/Fault
13 23
33
41
A1
S11
S21
42
S22
14
S34
24
34
CI
14 24
34
42
A2
13 23 33
41
S12
L11
IN
0
MM
RESET
AM
IN
PWR/Fault
S12
S22
A1 A2
S11 S21
34
L11
14
Y32
24
23
S34
SI
OUT
0
MM
RESET
AM
13
14
23
24
24
Volts
DMM
24
Volts
DMM
A1
A1
A2
A2
Acceptable Range
20.4…26.4V DC
CI
SI, DI, DIS, EM,
and EMD
+ + - -
24V DC
L N
A2 13
S11 S12A1
Temporarily remove the protective ground
connection for troubleshooting. Reconnect
ground after completing.
PELV
Power
Supply
AC
Power
Supply
GSR Safety Relay
+24V Common
+24V DC
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