Siemens SINAMICS G120D Original Instructions Manual page 238

Setting functions
8.9 Safe Torque Off (STO) safety function
The STO safety function is standardized
The STO function is defined in IEC/EN 61800-5-2:
"[...] [The inverter] does not supply any energy to the motor which can generate a torque (or
for a linear motor, a force)."
The STO inverter function complies with what is defined in the standard.
The distinction between Emergency Off and Emergency Stop
"Emergency Off" and "Emergency Stop" are commands that minimize different risks in the
machine or plant.
The STO function is suitable for achieving an emergency stop but not an emergency off.
Risk:
Measure to minimize
risk:
Command:
Classic solution:
Solution with the STO
safety function
integrated in the
drive:
238
Risk of electric shock:
Safe switch off
Switching off the electric power
supply for the installation, either
completely or partially.
Emergency Off
Switch of the power supply:
STO is not suitable for safely
switching of an electric voltage.
Operating Instructions, 04/2014, FW V4.7, A5E34261542B AA
Risk of unexpected motion:
Safely stop and safely prevent
restarting
Stopping or preventing the dangerous
movement
Emergency Stop
Switch-of the drive power supply:
Select STO:
It is permissible that you switch of the
inverter supply voltage as well.
However, switching off the voltage is
not required as a risk-reduction
measurement.
Converter with control units CU250D-2