S9407-AB-HBK-010 Datasheet, PDF (24/276 Pages) Glenair, Inc. – HANDBOOK OF SHIPBOARD ELECTROMAGNETIC SHIELDING PRACTICES

S9407-AB-HBK-010, Rev. 2
Pipe Size
Nominal ID
(inches)
1/4
3/8
1/2
3/4
1
1-1/4
1-1/2
2
2-1/2
3
Table 2-1. Carbon Steel Pipe (MIL-P-24691/1)
Grade
Per
MIL-P-24691/1
A
A
B
B
B
B
B
B
B
B
Min Wall
Thickness
(inches)
0.120
0.126
0.147
0.154
0.179
0.191
0.200
0.218
0.276
0.300
OD
(inches)
0.540
0.675
0.840
1.050
1.315
1.660
1.900
2.375
2.875
3.500
Thread Size
NPSM
(threads/in.)
1/4 - 18
3/8 - 18
1/2 - 14
3/4 - 14
1 - 11-1/2
1-1/4 - 11-1/2
1-1/2 - 11-1/2
2 - 11-1/2
2-1/2 - 8
3-8
Minimum
Torque
(lb-ft)
25
25
50
100
100
100
100
100
100
100
2.4 RIGID CONDUIT INSTALLATION
2.4.1 Nontopside and Topside Use of Rigid Conduit
The rigid conduit described herein is intended for submarine and non-topside use to provide
cable shielding against cable-to-cable and equipment-to-cable coupling. Conduit employed for
topside use is addressed by MIL-STD-1310 and is intended to provide shielding from electromagnetic
pulse (EMP) and radiating antennas. (The MIL-STD-1310 definition for conduit includes circular tube
or pipe and square or rectangular sheet-metal trunks which enclose cables for shielding protection.)
2.4.2 Grounding Requirements for Rigid Conduit
The shielding effectiveness provided by rigid conduit, against a magnetic field caused by
structure current flowing on its outer surface, is proportional to the number of "skin depths" in the
conduit wall material. This is discussed in detail in paragraph 7.3.2 of section 7. In most cases the
0.120-inch minimum wall thickness of the rigid conduit provides sufficient attenuation: approximately
30 dB at 200 Hz. This will give adequate protection against structure-current effects. Protection
increases exponentially with frequency and effectively shields the internal cables from EMI caused by
structure current flowing on the conduit.
In view of the preceding characteristics, rigid conduit shall be grounded in accordance with
MIL-STD-1310. It states that conduits 10 feet or longer shall be bonded to ground potential at a point
not greater than 5 feet from each end. It also states that class "B" bonding is acceptable; however,
where it is not inherent in the installation of the conduit, bond straps are required. Figure 2-1
illustrates the methods of grounding by means of bond straps.
Grounding conduit at more than one point along its run constitutes "multiple-point grounding."
This term includes inadvertent grounding of conduit as well as intentional grounding of conduit that is
installed in accordance with approved plans. Although multiple-point grounding of the conduit is the
recommended configuration, isolation of the conduit from the equipment cabinet may be necessary to
reduce structure-current flow on the cabinet and its effect on susceptible equipment housed therein.
(See figure 5-20, "RP 2440 Adapter, Nonmetallic" for isolation of conduit-end from its termination).
CHANGE 1 of Revision 2
2-2