ABB ACQ810-04, Hardware Manual, Page: 57 / 144

Planning the electrical installation 57
Implementing the Safe torque off (STO) function
The drive supports the Safe torque off function according to standards
EN 61800-5-2:2007; EN 954-1:1997; IEC/EN 60204-1:1997; EN 61508:2002 and
EN 1037:1996.
The Safe torque off function disables the control voltage of the power semiconductors of
the drive output stage, thus preventing the inverter from generating the voltage required to
rotate the motor (see diagram below). By using this function, short-time operations (like
cleaning) and/or maintenance work on non-electrical parts of the machinery can be
performed without switching off the power supply to the drive.
Start up and validate the Safe torque off function according to Safe torque off function for
ACS850 and ACQ810 application guide (3AFE68929814 [English]). The manual includes
the safety data for the function.
WARNING! The Safe torque off function does not disconnect the voltage of the
main and auxiliary circuits from the drive. Therefore maintenance work on the
electrical parts of the drive or the motor can only be carried out after isolating
the drive system from the main supply.
Note: It is not recommended to stop the drive by using the Safe torque off function. If a
running drive is stopped by using the Safe torque off function, the drive will stop by
coasting. If this causes danger or is not acceptable, the drive and machinery must be
stopped using the appropriate stopping mode before using the Safe torque off function.
For more information, see Safe torque off function for ACS850 and ACQ810 drives
application guide (3AFE68929814 [English]).
+24 V
XSTO:1
XSTO:2
XSTO:3
XSTO:4
U2/V2/W2
Control
circuit
UDC+
UDC-
ACQ810-04
Output stage
(1 phase shown)
Safe torque off
connection on JCU
Activation switch
Notes:
• The contacts of the activation
switch must open/close within
200 ms of each other.
• The maximum cable length
between the drive and the
activation switch is 25 m (82 ft)