"System Wiring Guidelines"
Headquarters
Unitronics (1989) (R"G).
Unitronics Building, Airport City
P.O.B. 300, Ben Gurion Airport, Israel 70100
Tel: + 972 (3) 977 8888 Fax: + 972 (3) 977 8877
Technical Note Document - 09/2013
System Wiring Guidelines
Good grounding and wiring practices are essential to the performance of electronic
systems. This document provides practical guidelines for system grounding and wiring
that can optimize performance and increase electromagnetic noise immunity.
When wiring, follow the local safety guidelines along with those provided in the
documentation of each device.
NOTE The guidelines provided herein supplement the documentation of each of the
devices, which must be read, understood and followed.
NOTE After installation, check your system periodically, in particular after installing
new machinery in and near the system.
Devices emitting high EMF
High voltage, high current, and high frequency circuits such as power supplies, high
power converters and amplifiers, contactors and solenoids, motors and motor-drives
may cause severe electro-magnetic disturbances that may affect the operation of other
nearby computerized devices such as PLCs or I/O modules. Those high voltage, high
current, and high frequency circuits should not share the same cabinet with PLCs or
I/O modules.
If this is unavoidable, within the cabinet, either:


Physically separate these sources from PLCs and I/O modules with large metal
earthed plates. Such a plate should be large enough to partition the cabinet into
two sections.
Separate these sources and their cabling from PLCs and I/O modules as
described in the section Wiring Separation.
Wiring Separation
 Separately wire each of the following groups:
Group 1
Group 2

Communication lines;

AC I/O lines;

Low voltage, low noise supply and
I/O lines (e.g. analog and low-speed
digital I/Os).

Noisy supply and I/O lines (e.g.
inductive or capacitive loads supplies
and high speed digital I/Os).

Do not run wires of those two groups together in parallel. If this is not possible,
keep the parallel travel distance as short as possible.

If the wires of those two groups must cross each other, cross them at a 90˚ angle.
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Enclosing and Earthing
It is recommended to use a closed metallic cabinet for installation. This will
significantly improve immunity from electromagnetic interference.


Make sure that both the cabinet and cabinet door are properly earthed. Please refer
to the cabinet manufacturer instructions for proper installation and earthing.

When you earth devices, minimize wire impedance by using a wire that is as short
and thick as possible, less than 1m (3.3’) in length, minimum thickness 14 AWG (2
mm2).
Connect the line to nearest possible grounding point in the cabinet, preferably a
grounding plate or the cabinet body. Ensure good contact between the wire
termination and the metallic surface by removing or scratching any non-conductive
coating, such as paint. This can be achieved, for instance, by using toothed
washers.
I/O Wiring: General Guidelines
 Route each I/O signal / signal-group along with its dedicated common wire. This
wire serves as a signal return path and increases interference immunity.
Connect common wires at their respective pins on the I/O module. Please refer to
the module installation guide for details.

When wiring analog and high-speed I/O signals:







Use shielded twisted pair cables.
Do not use the shield as a signal or as a return conductor.
Connect the cable shield to the earth of the system - preferably to the metal
cabinet chassis.
Note that the shield must be connected only at one end of the cable; typically,
earthing the shield at the I/O module end performs better. However, in some
cases, earthing the shield at both ends of the cable is preferable; in such cases,
in order to eliminate ground currents through the shield, it is necessary to earth
the shield through a 100nF capacitor at one of its ends, preferably at the one
which is far from the I/O module.
Keep shield connections as short as possible.
Ensure shield continuity when extending shielded cables.
Plan your routing paths carefully:


Choose the shortest available path and avoid unnecessarily excessive wire
lengths;
Follow the guidelines outlined in the Wiring Separation section above.
Signal (Communication, I/O) Line Filtering
Extra signal line filtering may improve the system’s immunity to EMI.
If signal-line filtering is required, please use the following guidelines in addition to
the guidelines provided by the filter manufacturer:

Place the filter as close as possible to the target device(s), maximum
recommended distance is 10cm (4").

Signal lines can be filtered using rounded ferrite cores. Depending on the ferrite
core and the type of interference, winding the wire through the ferrite core
multiple times may increase their effectiveness.
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Always pass both the signal and signal return wires thru the ferrite core.
If multiple I/O lines share the same common return wire, pass all of these I/O lines
and their return wire through the same ferrite core.
Power-line Filtering
Extra power line filtering may improve the system’s immunity to EMI.
If power-line filtering is required, please use the following guidelines in addition to the
guidelines provided by the filter manufacturer:



Use of power-line filters that comprise an earthing terminal is
recommended. Connect the filter earthing terminal as explained in the
section Enclosing and Earthing.
Place the filter as close as possible to the target device(s), maximum
recommended distance is 10cm (4").
When using ferrite cores, depending on the ferrite core and the type of
interference, winding the wire through the ferrite core multiple times may
increase their effectiveness.
The information in this document reflects products at the date of printing. Unitronics reserves the right, subject to all applicable laws, at any time, at its sole discretion, and
without notice, to discontinue or change the features, designs, materials and other specifications of its products, and to either permanently or temporarily withdraw any of the
forgoing from the market.
All information in this document is provided "as is" without warranty of any kind, either expressed or implied, including but not limited to any implied warranties of
merchantability, fitness for a particular purpose, or non-infringement. Unitronics assumes no responsibility for errors or omissions in the information presented in
this document. In no event shall Unitronics be liable for any special, incidental, indirect or consequential damages of any kind, or any damages whatsoever arising out of or in
connection with the use or performance of this information.
The tradenames, trademarks, logos and service marks presented in this document, including their design, are the property of Unitronics (1989) (R"G) Ltd. or other third parties
and you are not permitted to use them without the prior written consent of Unitronics or such third party as may own them
[DOC00002-A8] 09/13
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