S9407-AB-HBK-010 Datasheet, PDF (171/276 Pages) Glenair, Inc. – HANDBOOK OF SHIPBOARD ELECTROMAGNETIC SHIELDING PRACTICES

S9407-AB-HBK-010, Rev. 2
7.3.6 Finish
After annealing (where required), and prior to final assembly, the parts requiring painting shall
be given one coat of pretreatment primer and two coats of enamel. In some cases a cadmium-plated
finish may be required for the enclosure and cover assemblies.
7.3.6.1 Finish at Enclosure-Cover Interface
The mating surfaces of the enclosure and its cover which come in contact with the EMI gasket
shall be cleaned to the bare metal, be free of all foreign materials, and remain unpainted to ensure a
metal-to-metal seal to prevent leakage of magnetic flux.
Each time thereafter that the enclosure is opened, the contact surfaces should be inspected
and, if necessary, cleaned to the bare metal before reattaching the cover.
If the enclosure is located in a corrosive environment, the contact surfaces between the
enclosure and its cover shall be protected with a conductive finish, such as cadmium plating, or other
conductive coating.
7.4 RECOMMENDED WIRING PRACTICES FOR USE IN SHIELDING ENCLOSURES
In order to optimize the EMI protection provided by shielding enclosures, particular attention
should be paid to the layout of wiring inside the enclosures. The size of the loop area formed by a pair
of conductors should be kept to a minimum by twisting the pair and by maintaining the twist as close
to the terminals as practicable. In addition, the spacing between radiators and susceptors within the
enclosure should be maintained as a minimum in accordance with section 6 wherever practicable.
Figures 7-3, 7-4, and 7-5 illustrate various wiring practices.
The wiring practice shown in figure 7-3a is not recommended because it creates an
unnecessarily large pickup loop area (shaded area) which increases circuit susceptibility. Figure 7-3b
shows the recommended practice of keeping the conductor pairs short and tightly twisted to minimize
the pickup loop area.
The wiring practice shown in figure 7-4a is not recommended because of the increase in
cross-coupling caused by running susceptible (low-level) conductors too close to radiating (high-level)
conductors. Figure 7-4b shows the recommended practice for obtaining maximum spacing (see
section 6 for required spacing) between susceptible conductors and radiating conductors.
The wiring practice shown in figure 7-5a for a cable having shielded twisted pairs is not
recommended because the arrangement creates large pickup loop areas. Figure 7-5b shows the
recommended practice for terminating the shielded twisted pairs. The practice shown in figure 7-5b
allows the shield for each twisted pair to be brought close to the terminals. A general rule for good
wiring practice for shielded twisted pairs is to bring the shield as close as practicable to the end of the
twisted pair and maintain the twist between pairs as close to the terminals as practicable.
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