IDEC SG4 Type 4 Finger & Hand - Manual (Page 35)

Instruction Manual SG4-B Series
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4.2. Ground connection
SG4 safety light curtain units are preset for easy ground connection.
A special compartment, positioned onto caps and marked with the
special symbol shown in Figure 21, allows connection with ground
cable by means of an additional screw coming with the equipment.
Fig. 21
Ground connection configuration is the most common and
guarantees the best immunity against electromagnetic disturbances.
SG4-B can function even without ground connection.
This condition has to be carefully evaluated according to the EMC
disturbance immunity and necessary insulation class considering the
plant or entire system where the light curtain is installed.