7.4.5.2 Grounding the Cable Shield
Equipotential bonding refers to using metal parts to make ground potential everywhere in the installation the same, the system
ground. If the ground potential of all the devices is the same, you can prevent current from flowing through paths that are not
designed to have current. You can also shield cables efficiently.
An error in the equipotential bonding can cause bad quality or malfunction of the fieldbus communication. It is not easy to find an
error in equipotential bonding. It is also not easy to correct errors in large installations after commissioning. Thus, in the planning
phase it is important to plan the installation to get good equipotential bonding. In the commissioning phase, make the equipotential
bonding connections carefully.
Do grounding with low HF impedance, for example, via backplane mounting. If ground connection wires are necessary, use wires that
are as short as possible. Note that paint coating acts as an insulator on metal and prevents grounding. Remove paint coating before
doing grounding.
This chapter describes the principles of cable shield grounding. Notice that the internal RS485 fieldbus in VACON 100
®
products does
not have jumpers for grounding options.
Connect the cable shield directly to the frame of the AC drive (see illustration 36 and illustration 38).
Illustration 36: Grounding in noisy environment with good equipotential. If potentials at points A, B, C and D are very different and cannot be
made similar, cut the shields as in Illustration Grounding in noisy environment with poor equipotential.
If ground potentials of the connected devices are different, cable shield that is connected at both ends causes current to flow in the
shield. To prevent this, the cable shield must be disconnected or cut at some point between the devices (see illustration 37).
When disturbances are strong, the cable shield can be exposed and then 360 degrees grounded directly to the AC drive ground (see
illustration 38). When the connection is made like in illustration 37, grounding should be done at a location nearest to the place where
the disturbances meet the cable.
Illustration 37: Grounding in Noisy Environment with Poor Equipotential. An Example of Cutting the Shield.
We recommend grounding the cable shield as in examples A and C (see illustration 38). Do not ground the cable shield as in example
B.
Control Unit
Operating Guide | VACON® 100 Wall-mounted Drives
AQ298036140958en-000101 / DPD01711| 79
Danfoss A/S © 2019.05
To Next Page
Loading...
