Figure 2-9, Figure 2-10, Remote mounted hmis or converters – Innotech Device Network Cabling User Manual

Page 22: Figure 2-9: figure 2-10

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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 differences 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 difference 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 off 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 differences between networks

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