Licht MFC-200/P, Техническое руководство, Страница: 22 / 28

Licht
http://www.licht-labs.com
info@licht-labs.com
Rev. A2 (23–01–09) MFC-200/P Technical Manual 21
Important considerations
The installation of electronic devices in substations should conform with the recommen-
dations given by recent international standards. The most recent and detailed guide for
installations is IEC 61000-5-2:1997, which was based on decades of laboratory and field
research. We summarize below some of the guidelines contained in IEC 61000-5-2:1997.
For further reading, we recommend the articles and application notes available on our
web site.
a. Shielded cables must be used for connecting potentiometric sensors, current loop
outputs, RS-485 links and the auxiliary supply.
b. Cables must be segregated in trays, ducts or conduits according to their functions.
In particular, power cables must never be routed in the proximity of signal cables,
even if these are shielded. The minimum distances which must be observed are
described in IEC 61000-5-2:1997 and in articles available on-line at this product’s
web page.
c. The electrical continuity of cables, ducts, trays and conduits must be preserved up
to frequencies in the order of MHz, over all their extension, including curves and
junctions. In order to guarantee this continuity, joints and bonds should present
electrical contact along each cable, duct or tray’s transversal section. In particular,
trays should be bonded with seam-welded joints (best), U-brackets with multiple
fixings (ok) and never with wires.
d. Shielded cables should present no gaps in their screens along their lengths. 360
◦
bond-
ing should be performed instead.
e. Should there be unshielded sections (for example, near terminal block connections),
these should be short as possible.
f. Trays, ducts and conduits must be electrically continuous, and must be grounded
at both ends. In this configuration, trays, ducts and conduits provide shielding
and also perform as parallel earth conductors.
g. Shielded cables should also have their screens bonded at both ends. It is extremely
important that the tray, duct or conduit which contains each cable is also grounded
at both ends, allowing it to perform as a parallel earth conductor. In the absence
of a parallel earth condutor, the cable screens will be exposed to extremely high
currents which will severely compromise their operation.
h. RS-485 pairs must be terminated at both ends by 120 Ω resistors.