Figure 4-25 Category 3 Interlock Using Safe Torque; Figure 4-26 Use Of Contactor And Relay To Avoid The Need For Protected Wiring - Emerson unidrive sp User Manual

Safety Mechanical
Product
Information information Installation
The safety function of the example circuit is to ensure that the motor
does not operate when the interlocks are not signalling a safe state. The
safety relay is used to check the two interlock channels and detect faults
in those channels. The stop/start buttons are shown for completeness as
part of a typical arrangement, they do not carry out a safety function and
are not necessary for the safe operation of the circuit.
Figure 4-25 Category 3 interlock using SAFE TORQUE OFF
(SECURE DISABLE) with protected wiring
Stop
Reset
Start
Safety
relay
Interlocks
In the conventional system, a contactor failure in the unsafe direction is
detected the next time the safety relay is reset. Since the drive is not part
of the safety system it has to be assumed that AC power is always
available to drive the motor, so two contactors in series are required in
order to prevent the first failure from causing an unsafe event (i.e. the
motor driven).
With SAFE TORQUE OFF (SECURE DISABLE) there are no single
faults in the drive which can permit the motor to be driven. Therefore it is
not necessary to have a second channel to interrupt the power
connection, nor a fault detection circuit.
It is important to note that a single short-circuit from the Enable input
(SAFE TORQUE OFF (SECURE DISABLE)) to a DC supply of
approximately +24V would cause the drive to be enabled. For this
reason, Figure 4-25 shows the wire from the Enable input to the safety
relay as "protected wiring" so that the possibility of a short circuit from
this wire to the DC supply can be excluded, as specified in ISO 13849-2.
The wiring can be protected by placing it in a segregated cable duct or
other enclosure, or by providing it with a grounded shield. The shield is
provided to avoid a hazard from an electrical fault. It may be grounded
by any convenient method, no special EMC precautions are required.
If the use of protected wiring is not acceptable, so that the possibility of
this short circuit must be allowed for, then a relay must be used to
monitor the state of the Enable input, together with a single safety
contactor to prevent operation of the motor after a fault. This is illustrated
in Figure 4-26.
N
NOTE
The auxiliary relay K2 must be located in the same enclosure and close
to the drive, with its coil connected as closely as possible to the drive
enable / SAFE TORQUE OFF (SECURE DISABLE) input.
Unidrive SP Free Standing User Guide
Issue Number: 1
Getting Basic
Electrical
Installation Started parameters
+24V
Drive run
(Pr
Drive
SD
Protected wiring
(screened or
segregated)
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Running SMARTCARD
Optimization
the motor operation
Figure 4-26 Use of contactor and relay to avoid the need for
protected wiring
Reset
10.02 )
Two-channel
interlocks
M
3 ~
Onboard Advanced Technical
PLC parameters Data
+24V
Stop
K1
Start
K2
Safety
relay
K1 K2
UL Listing
Diagnostics
Information
SD
Drive
K2
K1
M
3 ~
71