Manual
© Mass Electronics Pty Ltd 2007
Innotech Device Network Cabling Installation Instructions
Edition 3.0 dated 05.12.2013
Page 22
Generally in all installations care must be taken when selecting the best earth point. Good earth points are usually
close to the earth stake and away from heavy power equipment. Heavy power equipment causes earth currents
and therefore the earth point is subject to potential dierences in current interference, and as such is usually not a
good choice.
NOTE
2. In the wrong example below, the cable run for the NET comms is significantly longer than that
of the Global comms. This can cause an earth potential dierence between the net and global
screen resistances and therefore unequal current flows which can cause network problems.
Figure 2-9: Remote Mounted HMIs or Converters
To rectify the above incorrect wiring situation you must use one of the following options:
• Branch o earth screens at the single comms earth point where the Net cable is routed through the
HMI without the Global cable. This is the Hard Earth.
• Keep the Net and Global network cables the same length and following the same path
Screen Wires must
be taken from Global
comms, and to and
from the HMI on the
Net comms. All screens
must be terminated to
a Hard Earth
Figure 2-10: Options to eliminate earth potential dierences between networks