S9407-AB-HBK-010 Datasheet, PDF (156/276 Pages) Glenair, Inc. – HANDBOOK OF SHIPBOARD ELECTROMAGNETIC SHIELDING PRACTICES

S9407-AB-HBK-010, Rev. 2
Section 7
SHIELDING ENCLOSURES, BONDING AND GROUNDING
7.1 INTRODUCTION
This section covers the requirements for construction and application of metal enclosures,
such as terminal boxes, junction boxes, and connector hardware, that are used to shield cable
terminations and electrical components from external electromagnetic radiation. The boxes also
serve to attenuate electromagnetic radiation produced by electrical components enclosed within the
box.
In an installation where a terminal box (or junction box) is located in a cable run which is
completely enclosed in shielding conduit, that box shall be considered an extension of the shielding
conduit and shall be manufactured of a material and thickness which provides, as a minimum, the
same shielding effectiveness as the shielding conduit.
7.2 SCOPE
This section contains details on the construction of shielding enclosures such as materials,
shielding effectiveness, and annealing instructions. This section also covers installation procedures
such as wiring practices and grounding requirements.
The shielding procedures in this section are limited primarily to enclosures in the below-decks
shipboard environment, and are directed primarily toward the low-frequency portion of the spectrum.
The reasons for this are:
a. Effective shielding against magnetic fields is more difficult to achieve at low frequencies
than at high frequencies. The greater "skin depth" at low frequencies dictates a
requirement for thicker material to obtain the necessary protection.
b. The bulk of below-deck EMI problems are related to the shipboard power system and
occur at frequencies below 100 kHz.
c. EMI problems are more tractable at frequencies above 100 kHz.
This section does not cover shielding enclosures employed in the topside shipboard
environment that require additional considerations. The two major considerations and requirements
are:
a. A 360-degree bonding of the shielding conduit at the enclosure penetration must be
installed to protect electrical and electronic circuits from electromagnetic radiation from
transmitting antennas, lightning, and electromagnetic pulse (EMP).
b. The enclosures must be made weather tight to maintain EMC.
7-1