Manual VIPA HMI
Chapter 3 Installation Guidelines
HB160E - TP - RE_610-3B4I1 - Rev. 11/07
3-9
Potential differences can occur between different sections when controllers
and peripheral equipment are connected by means of non-isolated
connections or the screens of screened cables are connected at both ends
and grounded on different sections of the plant.
One reason for a potential difference can be that different sections of the
plant are powered from different power sources. These potential
differences must be reduced by means of equipotential bonding conductors
to ensure that the electronic equipment employed on the plant operates
properly.
•
The lower the impedance of the equipotential bonding conductor, the
higher the effectiveness of potential equalization.
•
The impedance of the equipotential bonding conductor must not exceed
10% of the impedance of the screen where screened signal lines are
connected between the different sections of the plant and the screening
is connected to ground/neutral on both sides.
•
The cross-sectional area of the equipotential bonding conductor must be
calculated to carry the maximum equalization current. The following
cross-sections have been successfully employed:
- 16mm
2
Cu for equipotential bonding conductors up to 200m
- 25mm
2
Cu for equipotential bonding conductors exceeding 200m.
•
Use copper or galvanized steel for equipotential bonding conductors.
These must be connected to ground/neutral by means of large-surface
connections that are protected from corrosion.
•
The equipotential bonding conductor should be installed in such a
manner that it includes the smallest surface between the bonding
conductor and the signal lines.
Screening is one method commonly used to reduce (attenuate) the
interference pick-up from magnetic, electrical or electromagnetic fields.
•
Interference on screens is conducted to ground by the conductive
connection between the screen and the screening rain/enclosure. To
avoid interference from these currents it is very important that the
neutral connection is a low-impedance connection.
•
You should only use of cables that are provided with a braided screen.
The degree of screening should be more than 80%.
•
Avoid cables with foil-type screens as the foil is easily damaged by
tension and pressure at the point of attachment; this can result in
reduced effectiveness of the screening action.
•
As a rule you should always ground the screens of cables on both ends.
This is the only way in which you can ensure that high frequency
interference is attenuated properly.
Equipotential
bonding
Rules for
equipotential
bonding
Screening of lines
and cables
