2.8
WAVEGUIDE ASSEMBLIES
Waveguide-below-cutoff (WBC) protection shall be provided for all piping,
ventilation, fiber optic cable penetrations and microwave communications
barrier penetrations of the HEMP electromagnetic barrier. These WBC
penetrations shall be protected with cutoff frequencies and attenuation no
less than the EM shielding effectiveness values listed herein. The cutoff
frequencies shall be no less than 1.5 times the highest frequency of the
shielding effectiveness. For 1 GHz, the maximum rectangular linear
diagonal dimension shall be 100 mm 4 inches and the maximum circular
diameter shall be 100 mm 4 inches. The length-to-cell cross-section
dimension ratio of the waveguide shall be a minimum of [5:1 to attain 100
dB] [3:1 to attain 50 dB]. Penetration locations shall be arranged to
facilitate installation and testing by minimizing the number of locations.
Waveguides of each assembly type shall be factory tested in accordance with
IEEE Std 299 and Table I of this specification.
2.8.1
Waveguide-Type Air Vents
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NOTE: Occurrence of dissimilar metals will use
corrosion resistant design.
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Each ventilation WBC array shall be a honeycomb-type air vent with a core
fabricated of corrosion resistant steel as shown on the drawings.
Waveguide construction shall include heavy frames to dissipate the heat of
welding to the shield. A welded WBC array shall be constructed from sheet
metal or square tubes. Array cells shall be formed by welding the sheets
at intersections or welding adjacent tubes along the entire length of the
WBC section. The maximum cell size shall be 100 mm 4 in on a diagonal.
The length of the WBC section shall be at least five times the diagonal
dimension of the cells. Air vents shall be a permanent part of the
shielded enclosure and shall have a shielding effectiveness equal to that
of the total enclosure. Static pressure drop through the vents shall not
exceed 3.4 gpscm 0.01 inch of water at an air velocity of 305 m/s 1000 fpm.
Waveguides for air vents (honeycomb) shall have access doors in duct work
for maintenance. The frame of the honeycomb panel shall be [welded]
[bolted] into the penetration plate [with continuous circumferential EM
welds.] [with bolts 75 mm 3 inches on center.] Welds for fabrication and
installation of honeycomb waveguide panels are primary shield welds and
shall be inspected as indicated. Acceptance testing of all honeycomb
panels shall be included with the final acceptance test. Conductors, such
as wires and louver operating rods, shall not pass through the waveguide
openings.
2.8.2
Piping Penetrations
All piping penetrations of the HEMP barrier to include utility piping, fire
mains, vent pipes, and generator and boiler exhausts shall be made with
piping WBC sections. The WBC material shall be steel with a composition
suitable for welding to the HEMP shield. The minimum wall thickness shall
be 3.2 mm 0.125 inch. The maximum inside diameter shall be 100 mm 4 inch
or a metallic honeycomb insert with a maximum cell dimension of 100 mm 4 in
shall be installed. The WBC section shall have an unbroken length of at
least five diameters to form a minimum cutoff frequency of 1.5 times the
highest frequency of the shield effectiveness. The piping WBC section
shall be circumferentially welded or brazed to the HEMP shield, pipe
sleeve or a penetration plate as shown on the drawings. Generator and
SECTION 13095A
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