S9407-AB-HBK-010 Datasheet, PDF (256/276 Pages) Glenair, Inc. – HANDBOOK OF SHIPBOARD ELECTROMAGNETIC SHIELDING PRACTICES

S9407-AB-HBK-010, Rev. 2
APPENDIX F
GUIDELINES FOR CABLE SPACING AND SHIELDING REQUIREMENTS
IN THE PRESENCE OF DC GENERATING COILS
F-1 INTRODUCTION
Black iron pipe and highly permeable flexible shielding conduit is used in many shipboard cable
installations to reduce the likelihood of electromagnetic interference (EMI). Section 6 of this document
gives information regarding the application of shielding and spacing requirements in wireway design.
Concern has been raised over the effects that dc generating coils have on the shielding and
spacing requirements of Section 6. These fields can be as high as 20 gauss. Test results have shown
that the ac shielding effectiveness of flexible shielding conduit (Section 3) is reduced when subjected to dc
magnetic fields. These tests have also shown that there is no significant reduction in the ac shielding
effectiveness of black iron pipe (Section 2) when it is subjected to dc magnetic fields.
F-2 SCOPE
This section describes shielding and spacing requirements for platforms which contain dc
generating coils. These requirements are in addition to the Section 6 shielding and spacing requirements.
These requirements are to be used when flexible shielding conduit is used, they do not apply when black
iron pipe is used. The requirements in this section deal only with cables shielded with flexible shielding
conduit.
F-3 CABLE CATEGORIZATION WITH DC FIELDS
When only one cable (either the radiator or the susceptor) is shielded with flexible shielding conduit
the susceptor group number for S1, S2 and S4 type cables will be reduced by one group. Table F1
indicates this change and provides an example. When both cables (susceptor and radiator) are shielded
with flexible shielding conduit the susceptor group number for S1, S2, and S4 type cables will be reduced
by two groups. Table F-2 indicates this change and provides an example. Once the modified susceptor
category has been determined, the spacing and shielding requirements can be obtained by using the
procedures described in Section 6.
Table F-1. Conduit On One Cable
Cable/Conduit
Categorization
S1-X
S2-X
S4-X
Example: S4-4
Categorization with
DC Fields
S1-(X-1)
S2-(X-1)
S4-(X-1)
S4-3
F-1