ABB AB91-1 HESG437479R1 HESG437899
Safe torque off (option +Q967)
The drive supports the Safe torque off (STO) function according to standards:
• EN 61800-5-2:2007
• EN ISO 13849-1:2008/AC:2009
• EN ISO 13849-2:2012
• IEC 61508 ed. 1
• EN 62061:2005/AC:2010
• EN /IEC 60204-1:2006/AC:2010
The function also corresponds to an uncontrolled stop in accordance with category 0
of EN/IEC 60204-1 and Prevention of unexpected start-up of EN 1037.
The STO may be used where power removal is required to prevent an unexpected
start. The 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.
An example circuit diagram is shown below.
Note: The Safe torque off function can be used for stopping the drive in emergency
stop situations. In the normal operating mode, use the Stop command instead. If the
Safe torque off function is activated when the drive is running, the control voltage of
the power semiconductors is cut off and the motor coasts to a stop. If this is not
acceptable, e.g. causes danger, the drive and machinery must be stopped using the
appropriate stopping mode before using this function.
Note concerning permanent magnet motor drives in case of a multiple IGBT
power semiconductor failure: In spite of the activation of the Safe torque off
function, the drive system can produce an alignment torque which maximally rotates
the motor shaft by 180/p degrees. p denotes the pole pair number.
For more information on the STO function and the relevant safety data, see

Terminal for the user connection
The STO function includes an ASTO board which is installed inside the drive module
at the factory.
This figure shows the location of the ASTO board and the terminal for the STO user
connection in the drive module.
Selecting the power cables
General rules
Dimension the mains (input power) and motor cables according to local
regulations:
• The cable must be able to carry the drive load current. See chapter Technical
data for the rated currents.
• The cable must be rated for at least 70 °C (158 °F) maximum permissible
temperature of conductor in continuous use. For US, see Additional US
requirements.
• The inductance and impedance of the PE conductor/cable (grounding wire) must
be rated according to permissible touch voltage appearing under fault conditions
(so that the fault point voltage will not rise excessively when a ground fault
occurs).
• 600 V AC cable is accepted for up to 500 V AC. 750 V AC cable is accepted for
up to 600 V AC. For 690 V AC rated equipment, the rated voltage between the
conductors of the cable should be at least 1 kV.
For drive frame size R5 and larger, or motors larger than 30 kW (40 hp), symmetrical
shielded motor cable must be used (figure below). A four-conductor system can be
used up to frame size R4 with up to 30 kW (40 hp) motors, but shielded symmetrical
motor cable is always recommended. The shield(s) of motor cable(s) must have
360° bonding at both ends.
Note: When continuous metal conduit is employed, shielded cable is not required.
The conduit must have bonding at both ends as with cable shield.
A four-conductor system is allowed for input cabling, but shielded symmetrical cable
is recommended. To operate as a protective conductor, the shield conductivity must
be as follows when the protective conductor is made of the same metal as the phase
conductors:
Compared to a four-conductor system, the use of symmetrical shielded cable
reduces electromagnetic emission of the whole drive system as well as the stress on
motor insulation, bearing currents and wear.
The motor cable and its PE pigtail (twisted shield) should be kept as short as
possible in order to reduce high-frequency electromagnetic emission, as well as
stray currents outside the cable and capacitive current (relevant in power range
below 20 kW).
Cross-sectional area of the phase
conductors
S (mm2)
Minimum cross-sectional area of the
corresponding protective conductor
Sp (mm2)
S < 16 S
16 < S < 35 16
35 < S S/2