ABB AC 800M, User Manual

Page: 69 / 118

Section 3 Fieldbus Topologies Shielding and data line connection
3BDS009029R5001 B 69
Shielding and data line connection
To prevent EMC interference from entering the device, the cable shield should be
connected to the functional ground of the device (generally the electrically
conductive case). This is done by connecting the cable shield to the metal case of the
Sub-D connector and the functional ground over a large area. With correct system
installation, small external sources of interference are led to ground through the
cable shield without causing interference in the data lines. Interference of this type
can largely be avoided with appropriate EMC measures such as EMC-compliant
system installation, EMC-compliant cable laying and measures that avoid large
ground potential differences.
The cable shield must be connected to the functional ground at both ends of the
cable by making a large-area connection to a grounded conductive surface. When
laying the bus cables, particular care should be taken to ensure that the cable shield
is connected to the shield grounding clamp over a large area.
The two PROFIBUS data lines are designated A and B. There are no regulations on
which cable core color should be connected to which of the two data terminals on
each fieldbus device; the sole requirement is to ensure that the same core color is
connected to the same terminal (A or B) for all field devices throughout the entire
system (
across all stations and bus segments ).
If the data transfer cable has data wires with red and green insulation, then the
following assignment should be used:
• Green data cable - Connector pin A
• Red data cable - Connector pin B
This rule applies to both the incoming and the outgoing data lines.
Bus spur lines
The use of passive bus spur lines should be avoided.
Programming and diagnostic devices which are attached to the bus for example
during commissioning are generally connected using their own cable which acts as a
bus spur line. In such cases, you should use active bus tap-off devices (for example
bus terminals, repeaters, active cables etc.).