Hirschmann RS20 series User Manual page 10

 Provisions shall be made to prevent the rated voltage from being
exceeded by transient disturbances of more than 119 V.
 Connectors shall be connected or disconnected exclusively in dead-
voltage state.
 DIP switches shall be switched exclusively in dead-voltage state.
The USB port shall remain disconnected.
10
Installation RS20/22/30/32/40
Release 05 12/2015