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W A R N I N G
NO ELECTRICAL SAFETY
When Safe Torque Off (STO) is activated by removing the 24 V DC voltage supply to terminal 37 and 38, it does not provide elec-
trical safety. The STO function itself is not sufficient to implement the Emergency-Off function as defined by EN 60204-1. Using
the STO function to implement Emergency-Off may lead to personal injury.
Emergency-Off requires measures of electrical isolation, for example, by switching off mains via an extra contactor.
W A R N I N G
RISK OF ELECTRICAL SHOCK
The Safe Torque Off (STO) function does not isolate mains voltage to the drive or auxiliary circuits. Only perform work on electri-
cal parts of the drive or the motor after isolating the mains voltage supply and waiting for the discharge time to elapse, as speci-
fied on the drive nameplate. Failure to isolate the mains voltage supply from the unit and waiting the time specified could result
in death or serious injury.
Do not stop the drive by using the STO function. If a running drive is stopped by using the function, the unit trips and stops
by coasting. If this limitation is not acceptable, for example because it causes danger, use the appropriate stopping mode to
stop the drive and machinery before using the STO function. Depending on the application, a mechanical brake may be re-
quired.
STO is suitable for performing mechanical work on the drive system or affected area of a machine only. It does not provide
electrical safety. STO must not be used as a control for starting and/or stopping the drive.
W A R N I N G
RESIDUAL ROTATION
The STO function can be used for asynchronous, synchronous, and permanent magnet motors. Two faults can occur in the power
semiconductor of the drive. When using synchronous or permanent magnet motors, a residual rotation can result from the faults.
The rotation can be calculated to angle = 360/(number of poles). The application using synchronous or permanent magnet
motors must consider this residual rotation and ensure that it does not pose a safety risk. The situation is not relevant for
asynchronous motors.
N O T I C E
When designing the machine application, consider the timing and distance for a coast to stop (STO). For more information re-
garding stop categories, refer to EN 60204-1.
1.11.2 Wiring and Configuring Safe Torque Off
Safe Torque Off (STO) is designed to stop the drive in emergency stop situations. It can be used for asynchronous, synchronous, and
permanent magnet motors. When the STO function is activated, the drive issues an alarm, trips the unit, and coasts the motor to a
stop. The STO function is activated by removing the voltage at terminals 37 and 38 on the drive.
Procedure
Remove the jumper between control terminals 12 (24 V), 37, and 38 (see illustration 2.11). Cutting or breaking the jumper is
not sufficient to avoid short-circuiting.
Connect a dual-channel safety device (for example safety PLC, light curtain, safety relay, or emergency stop button) to ter-
minals 37 and 38 to form a safety application. The device must comply with the required safety level based on the hazard
assessment. Illustration 2.12 shows the wiring schematic of STO applications where the drive and the safety device (A) are
in the same cabinet and the drive provides the safety voltage. Illustration 2.13 shows the wiring schematic of STO applica-
tions where external supply is used. The safety device is shown by the letter (A).
Complete the wiring according to the instructions and:
Eliminate short circuit risks.
Ensure that the STO cables are shielded if they are longer than 20 m (65.6 ft) or outside the cabinet.
Connect the safety device directly to terminals 37 and 38.
Configure how the drive should resume operation after Safe Torque Off has been activated. Follow the instructions in
. If using the automatic restart, ensure that all requirements according to ISO 12100 paragraph
6.3.3.2.5 are fulfilled.
AN41533976851001-000101 /
130R1264
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Danfoss A/S © 2022.06
VLT® Midi Drive FC 280
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