The Safe torque off function 353
Wiring
The following diagrams present examples of Safe torque off wiring for
• a single inverter unit (page 354)
• a frame n×R8i inverter unit (page 355)
• multiple inverter units (page 356)
• multiple inverter units when an external 24 V DC power supply is used (page 357).
For information on the specifications of the STO input, see chapter Control units of the
drive (page 337).
Activation switch
In the wiring diagrams below, the activation switch has the designation [K]. This represents
a component such as a manually operated switch, an emergency stop push button switch,
or the contacts of a safety relay or safety PLC.
• In case a manually operated activation switch is used, the switch must be of a type
that can be locked out to the open position.
• The STO inputs must be switched on/off within 200 ms of each other.
• An FSO-xx safety functions module or an FPTC-0x thermistor protection module can
also be used. For more information, see the module documentation.
Cable types and lengths
• Double-shielded twisted-pair cable is recommended.
• Maximum cable lengths:
• 300 m (1000 ft) between activation switch [K] and inverter control unit
• 60 m (200 ft) between multiple inverter units
• 60 m (200 ft) between external power supply and first inverter unit
• With frame n×R8i inverter units: 30 m (100 ft) between BCU control unit and last
inverter module in the chain.
Note: A short-circuit in the wiring between the switch and an STO terminal causes a
dangerous fault. Therefore, it is recommended to use a safety relay (including wiring
diagnostics) or a wiring method (shield grounding, channel separation) which reduces or
eliminates the risk caused by the short-circuit.
Note: The voltage at the STO input terminals of each inverter control unit (or frame R8i
inverter module) must be at least 17 V DC to be interpreted as “1”. The pulse tolerance of
the input channels is 1 ms.
Grounding of protective shields
• Ground the shield in the cabling between the activation switch and the control unit at
the control unit.
• Ground the shield in the cabling between two control units at one control unit only.
• Do not ground the shield in the cabling between BCU and R8i module, or between R8i
modules.
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