User manual

Chapter 5: Installation and Wiring
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Hardware User Manual, 4th Edition, Rev. B
5–4
Emergency Stop Circuits
Emergency stop (E-Stop) circuits are a critical part of automation safety. For each machine
controlled by a PAC, provide an emergency stop device that is wired outside the PAC and easily
accessed by the machine operator.
E-stop devices are commonly wired through a master control relay (MCR) or a safety control
relay (SCR) that will remove power from the PAC I/O system in an emergency.
MCRs and SCRs provide a convenient means for removing power from the I/O system during
an emergency situation. By de-energizing an MCR (or SCR) coil, power to the input (optional)
and output devices is removed. This event occurs when any emergency stop switch opens.
However, the PAC continues to receive power and operate even though all its inputs and
outputs are disabled.
The MCR circuit could be extended by placing a PAC fault relay (closed during normal PAC
operation) in series with any other emergency stop conditions. This would cause the MCR
circuit to drop the PAC I/O power in case of a PAC failure (memory error, I/O
communications error, etc.).
WARNING: For some applications, field device power may still be present on the terminal block even
though the PAC is turned off. To minimize the risk of electrical shock, remove all field device power
before you expose or remove PAC wiring.
Saw Arbor
E-Stop Power On
Use E-Stop and Master Control Relay
Limit
Switch
Master
Control
Relay (MCR)
L1 N
MCR
MCR
CR1
MCR
CR1
S
E
-Sto
p
P
o
w
e
r
On
U
se E-Stop and Maste
S
L1
M
C
R
MCR
EMERGENCY
STOP
Guard
Limit
Switch