laminated to one or both sides. Bolted construction
is used when a shielded facility's service life is
short, 10 years or less, or the system is required
to be demountable for change of location. This
system requires more maintenance than a welded
system and requires access to the panels. The EM
shield layout may restrict attenuation testing of
the enclosure. It is desirable for large facilities
to place the shield at least 1 meter (3.3 feet)
inside the exterior walls, although cost and
construction restrict this consideration. The floor
shielding can be tested by SELDS test but not by
IEEE Std 299 if it is on grade. The facility layout
must be carefully planned to allow for testing and
shield maintenance.
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3.3.1
Enclosure Panel Installation
Panels shall be installed in accordance with the shielding manufacturer's
recommendations. Shielding panels shall be handled and installed without
damaged to the shielding steel. Exposed surfaces shall be cleaned of dirt,
finger marks, and foreign matter resulting from manufacturing processes,
handling, and installation. Electrical conduits shall be installed as
close to the EM shield as possible. Framing-joining system bolts shall not
be used to mount material and equipment. Material and equipment which must
penetrate the shielded enclosure shall be seam welded or soldered to both
shielding surfaces.
3.3.2
Surface Preparation
Surfaces shall be cleaned and buffed to ensure good electrical contact with
shielding surface. Paint or other coverings on mating surfaces of special
boxes such as for fire alarm systems, buzzers, and signal lights, including
areas between box and cover, box and wall, and box and conduit, shall be
removed. Insulating material shall be removed to maintain a low-resistance
ground system and to ensure firm mating of metal surfaces.
3.3.3
Floor Panel Setting
A polyethylene film 0.15 mm 6 mil thick vapor barrier shall be placed over
the structural floor of the parent room before any other work is set
thereon. A 3 mm 1/8 inch thick layer of hardboard shall be provided over
this film with joints loosely butted. Over this layer an additional layer
of similar filler material of equal thickness as the projection of the
framing-joining member from the bottom surface of the floor panel shall be
provided leaving no more than 6 mm 1/4 inch of space between the hardboard
and the framing-joining member.
3.3.4
Framing-Joining System
Screws shall be tightened with a calibrated adjustable torque wrench and
equal torque shall be set for each screw. Proper torque values shall be in
accordance with the manufacturer's requirements.
3.3.5
Door Assemblies
The door shall be mounted to perform as specified.
The door shall be
through-bolted to the EM shield.
SECTION 13095A
Page 48
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