Page 302 - Programmable Logic Controllers, Fifth Edition - Mobile version

PLC system. The master control relay provides a means
of de-energizing the entire circuit that is not dependent on MCR is connected to interrupt power to the I/O rack in the
event of an emergency, but still allow power to be main-
software. The internally programmed MCR of a PLC is tained at the processor. Figure 13-3 shows the typical wir-
not sufficient to meet safety requirements. The hardwired ing for an AC power distribution with a master control

Disconnect switch

3-phase
supply

H 1 H 3 H 2 H 4

Step-down
transformer
Panel
X1 X2 ground bus
Fuse
L1 120 V Neutral

L1 N
Processor power supply Grounding
Gnd electrode

Multiple E-stops
Start
MCR
MCR

MCR

To common (L1) To neutral conn.
of 120 v AC of 120 v AC
input devices input modules

To L1 To neutral
of 120 v AC of 120 v AC
output modules output devices

L1 N
DC power
supply Gnd
V+ DC common

To common
To V+ of DC
input devices of DC input
modules
To common
To V+ of DC of DC output
output modules
devices

Figure 13-3 Typical wiring for an AC power distribution with a master
control relay.
Source: Courtesy Pilz GmbH & Co. KG.

PLC Installation Practices, Editing, and Troubleshooting Chapter 13 283

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