2 Engineering
2.8 Safe Torque Off (STO)
Rapid Link 5 · RAMO5 · RASP5 05/20 MN034004EN www.eaton.com 55
2.8.4.2 STO installation with external supply voltage (24 V DC)
The two connecting cables from the external power supply and the safety
relay to the pin 4 (STO+) and pin 3 (STO-) must be twisted cables.
This twisted pair must be routed inside a closed cable duct or conduit (ESC)
and must also be screened, with the corresponding cable screen being
earthed (PES).
The external control voltage should meet the following specifications:
Pin 3:
Pin 4:
STO-: 0-V connection to internal control
voltage
STO+:, logical high signal,
Input = 18 - 30 V DC
from the safety controller
Figure 21: STO installation with external control voltage
+24 V DC
100 mA
External Power
Supply
0 V
PES
Safety relay
PES
3
1
2
4
Rated control voltage 24 V DC
Voltage for the logical STO high signal 18 - 30 V DC
Current carrying capacity 100 mA
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