Master control relay – Rockwell Automation 1763 MicroLogix 1100 Programmable Controllers User Manual User Manual

Page 28

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Publication 1763-UM001D-EN-P - March 2011

26 Installing Your Controller

Master Control Relay

A hard-wired master control relay (MCR) provides a reliable means for
emergency machine shutdown. Since the master control relay allows the
placement of several emergency-stop switches in different locations, its
installation is important from a safety standpoint. Overtravel limit switches or
mushroom-head push buttons are wired in series so that when any of them
opens, the master control relay is de-energized. This removes power to input
and output device circuits. Refer to the figures on pages 28 and 29.

Place the main power disconnect switch where operators and maintenance
personnel have quick and easy access to it. If you mount a disconnect switch
inside the controller enclosure, place the switch operating handle on the
outside of the enclosure, so that you can disconnect power without opening
the enclosure.

Whenever any of the emergency-stop switches are opened, power to input and
output devices should be removed.

When you use the master control relay to remove power from the external
I/O circuits, power continues to be provided to the controller’s power supply
so that diagnostic indicators on the processor can still be observed.

The master control relay is not a substitute for a disconnect to the controller.
It is intended for any situation where the operator must quickly de-energize
I/O devices only. When inspecting or installing terminal connections,
replacing output fuses, or working on equipment within the enclosure, use the
disconnect to shut off power to the rest of the system.

ATTENTION

Never alter these circuits to defeat their function since
serious injury and/or machine damage could result.

TIP

If you are using an external DC power supply, interrupt
the DC output side rather than the AC line side of the
supply to avoid the additional delay of power supply
turn-off.

The AC line of the DC output power supply should be
fused.

Connect a set of master control relays in series with the
DC power supplying the input and output circuits.

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