Industrial Automation Wiring and Grounding Guidelines E115P
10
Connect one input directly to the L1 side of the line, on
the load side of the CRM contacts, to detect whether the
CRM contacts are closed. In the ladder logic, use this
input to hold off all outputs anytime the CRM contacts are
open. (Refer to your programming manual.) If you fail to
do this, closing the CRM contacts could generate transient
EMI because outputs are already turned on. To have
outputs turned on when CRM contacts are closing would
be analogous to squeezing the trigger on a hand tool as
you’re plugging it in.
Figure 8 – Ungrounded AC Power-Distribution System with Master-Control Relay
Notes:
1 To minimize EMI generation, connect a suppressor across an
inductive load.
2
In many applications, a second transformer provides power to the
input circuits and power supplies for isolation from the output circuits.
3 Connect a suppressor here to minimize EMI generation from the
net inductive load switched by the CRM contacts. In some
installations, a 1µf 220Ω suppressor or 2µf 100Ω suppressor has
been effective.
1LT
Step-Down
2
Transformer
FUSE
FUSE
1FU
L1
2FU
L2
3FU
L3
L1
L2
L3
Disc.
H
1
H
3
H
2
H
4
Suppressor
1
Incoming
AC
To Motor
Starters
X
1
X
2
+–
Back-Panel
Ground Bus
Multiple E-Stop
Switches
Start
CRM
CRM
L1 N or L2
GND
CRM CRM
Controller
Power Supply
Input
Module
Wiring
Arm
Output Module
Wiring Arm
Output
Actuator
To DC I/O
Actuators/
Sensors
User DC
Supply
Input
Sensor
Enclosure
Wall
Suppressor
1
Suppressor
3
2LT
CRM
The I/O circuits form a net
inductive load switched by
the CRM contacts. Therefore,
a suppressor is needed
across the line at the load
side of the CRM contacts.
Grounding-Electrode
Conductor to
Grounding-Electrode
System
Equipment-
Grounding
Conductors
Connect When
Applicable
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