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Is Coaxial cable necessary with STO?

Issue:
Is Coaxial cable necessary with STO?

Product Line:
ATV61, ATV71, Altivar 61, Altivar 71

Environment:
All

Cause:
N/A

Resolution:
Yes, coaxial shielded cable is a must due to safety rules.

Explanation:
When we use STO only, the coaxial shielded cable is mandatory to be SIL2. 
Because we use only one channel (no signal redundancy), in case of cable crushing :
•    the shielded cable will put the signal to 0 and so, no safety issue
•    When you have coaxial cable, no risk to have another potential to the STO, via another cable on same conduit
If you do not have shielded and coaxial cable, you have the risk to not detect the cable crushing and consequently not detect a safety stop.
So here, a shield is mandatory to reach the safety level and avoid safety issue on the machine.
 
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