ABB ACS850 series, Hardware Manual

Page: 42 / 120

Planning the electrical installation
42
Safe Torque Off
The drive supports the Safe Torque Off function according to standards
prEN 61800-5-2; 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.
WARNING! The Safe Torque Off function does not disconnect the voltage of the
main and auxiliary circuits from the drive. Therefore maintenance work on electrical
parts of the drive or the motor can only be carried out after isolating the drive system
from the main supply.
Note: If a running drive is stopped by using the Safe Torque Off function, the drive
will cut off the motor supply voltage and the motor will coast to stop.
For further information on the function, refer to Safe Torque Off Function, Application
Guide (3AFE68929814 [English]).
+24 V
XSTO:1
XSTO:2
XSTO:3
XSTO:4
U2/V2/W2
Control
circuit
UDC+
UDC-
ACS850-04
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)