Safe Torque Off - ABB ACS800 Hardware Manual

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Safe torque off

The drive supports the Safe torque off (STO) function according to standards
EN 61800-5-2: 2007; EN/ISO 13849-1: 2008, EN 60204-1: 2006; IEC 61508, EN
1037: 1995 + A1: 2008 and EN 62061: 2005. The function also corresponds to an
uncontrolled stop in accordance with category 0 of IEC 60204-1.
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 the 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.
Note: If you add or modify the wiring in the drive safety circuits, ensure that the
appropriate standards (eg, IEC 61800-5-1, EN 62061, EN/ISO 13849-1 and -2) and
the ABB guidelines are met.
Planning the electrical installation