S9407-AB-HBK-010 Datasheet, PDF (122/276 Pages) Glenair, Inc. – HANDBOOK OF SHIPBOARD ELECTROMAGNETIC SHIELDING PRACTICES

S9407-AB-HBK-010, Rev. 2
6.6.8 Spacing of Microwave Transmission Lines and Waveguides
Energy transmitted in the microwave region is normally restricted to the interior for the
waveguide or solid wall transmission line. For this reason, waveguides and solid wall transmission
lines are exempt from the spacing requirements of this document.
6.6.9 Installation Practice Regarding Excess Cabling
In addition to the requirements for cable-to-cable spacing, cable installation practices for EMC
require that excess cabling be removed, except where necessary, rather than coiled. The coiling of
cables can compromise cable-to-cable spacing and can result in an increase in common-mode
interference voltage.
6.7 CABLE SHIELDING REQUIREMENTS
When the cable-to-cable spacing requirements of figure 6-6 cannot be met, electromagnetic
shielding of cables must be applied using flexible or rigid metal conduit as specified in paragraphs
6.7.3, 6.7.4, and the procedures given in paragraph 6.8. The application of shielding to susceptors S3
and R4 through R8, when spacing requirements cannot be achieved, is to provide 20 dB of shielding
as a minimum requirement. When this minimum requirement is satisfied, zero inches of spacing is
permitted in all cases. Figure 6-7 gives values of shielding effectiveness, based on empirical
measurements, for the rigid and high-permeability, flexible metal conduits. Shield conduit
requirements are primarily dependent upon:
a. Spacing restrictions,
b. Frequency band of interest,
c. Type of shielding material selected, and
d. Signal level in the susceptible cable.
Wide variations in these parameters dictate the requirement that shielding be determined for each
individual case. In all cases where either flexible or rigid metal conduit can provide the required
shielding, flexible metal conduit shall be used.
6.7.1 Partial Shielding
Flexible or rigid shielding conduit may be used to enclose a portion of a cable run as an
alternative to enclosing the entire cable run. For example, where a sonar cable runs through several
compartments, and where shielding conduit is required in only one of those compartments, then
partial shielding is recommended. However, a sufficient length of shielding conduit must be used to
ensure the EMC of the cable. The use of partial shielding is subject to the following restrictions. (See
figure 6-10.)
a. The conduit used as a partial shield shall not be less than 4 feet in length.
Reprinted without change
6-9