• 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 contacts of the switch or relay must open/close within 200 ms of each other.
￭ Cable types and lengths
• Double-shielded twisted-pair cable is recommended.
• Maximum cable lengths:
• 300 m (1000 ft) between activation switch [K] and drive control unit
• 60 m (200 ft) between multiple drives
• 60 m (200 ft) between external power supply and first control unit
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 the drive must be at least 13 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 only.
• Ground the shield in the cabling between two control units at one control unit only.
The Safe torque off function 191
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