S9407-AB-HBK-010 Datasheet, PDF (34/276 Pages) Glenair, Inc. – HANDBOOK OF SHIPBOARD ELECTROMAGNETIC SHIELDING PRACTICES

S9407-AB-HBK-010, Rev. 2
3.3.1 Specification for Flexible Shielding Conduit
Appendix D of this document contains a specification that is invoked on flexible shielding
conduit purchased for use by the Navy. The specification provides detailed requirements that cover
the following types of conduit:
Type 1 conduit. Type 1 nonjacketed conduit is used in installations where ground or
structureborne currents are minimal along the path of the conduit, or where the cable being
shielded is not susceptible to interference from current flow on the conduit. (Conduit can
become a conductor for ground or structureborne currents through contacts with ground
potentials along the length of the conduit.)
Type 2 conduit. Type 2 rubber-jacketed conduit is used for shielding an extremely low level,
low frequency signal cable which would be susceptible to interference from current flowing on
the conduit. The rubber jacket prevents this current flow by electrically insulating the conduit
from unintentional ground contacts.
3.3.2 Qualified Products List
A qualified products list for flexible conduit for low frequency shielding is maintained for Navy
procurement purposes (see appendix C). It provides information concerning flexible conduit which
meets the requirements of the specification in appendix D. Manufacturers wishing to have their
products tested for qualification should submit samples in accordance with the instructions contained
in this specification. Conduit which is tested shall meet the requirements of appendix D in order to be
approved by NAVSEA and to be added to the qualified products list.
3.4 FLEXIBLE CONDUIT INSTALLATION
3.4.1 Nontopside and Topside Use of Flexible Conduit
The flexible shielding conduit described herein is intended for submarine and nontopside use
to provide cable shielding against magnetic field cable-to-cable and equipment-to-cable coupling.
Requirements for flexible conduits which are approved as cable shields for EMI and electromagnetic
pulse (EMP) protection in a ship's topside area are listed in MIL-STD-1310.
3.4.2 Grounding Requirements for Flexible Conduit
The shielding effectiveness provided by flexible shielding conduit, against structure current
flowing on its outer surface, is proportional to the number of "skin depths" in the conduit wall material.
This is described in detail in paragraph 7.3.2 of section 7. As frequency is lowered, the 0.008-inch
wall thickness of typical, high permeability, flexible shielding conduit provides only one "skin depth"
(8.686 dB of attenuation) at approximately 2 kHz. At 10 kHz approximately 20 dB of shielding is
provided by this conduit. The 20-dB value represents the minimum amount of protection required for
most shielding applications. It is for this reason that single-point grounding of the conduit, to reduce
structure-current flow, is required below 10 kHz for S4-1, S4-2 and S4-3 cable categories. Single-
point grounding requires the use of Type 2 (rubber-jacketed) conduit in which the rubber-jacket
insulates the conduit from unintentional ground contacts. A Type IV bond strap in accordance with
MIL-STD-1310 is required for grounding the conduit. (See figure 5-20, "RP2440 Adapter, Non-
metallic" for isolation of conduit-end from its termination.
Reprinted without change
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