Quantcast Signal Reference Subsystem - hdbk232a0102

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MIL-HDBK-232A
5.6.1.2  Signal reference subsystem.  The principle function of the signal
reference subsystem in a facility is to provide a common ground reference
throughout the facility which is the same for all equipment.  Secondary
functions are to provide a path to earth for induced static and noise. and to
serve as a ground plane for high-frequency signals between equipment.  These
functions are best provided by an equipotential ground plane which is
installed under, over, or beside all of the equipment in the technical area.
A horizontal plane is much more effective than a vertical plane in
capacitively coupling high-frequency signals to earth.  The plane should be
bonded (welded or brazed) to the main steel structure of the building and to
the EESS at multiple points.
5.6.1.2.1  Construction of the equipotential plane.  Several methods are
commonly used to construct an equipotential plane, including solid copper
sheeting and grids of copper wire.  A sheet of copper can be placed under
floor tile or carpet.  A grid of wire can be installed overhead in an
existing installation, or embedded in floors, walls, or ceilings in new
construction.  Commercially available copper grids with silver-soldered,
brazed, or welded joints may be used so long as the aperture is not more than
4 inches (100 mm) and the wire size is at least No. 6 AWG.  An overhead grid
may be fabricated on site using No. 1/0 AWG stranded copper wire for wall
members and No. 2 AWG stranded wire for cross members.  The cross members
should be installed in a 4 by 4 inch (100 mm by 100 mm) aperture cross-hatch
pattern.  The cross members are bonded to each crossover point and at the
ends to the wall members.
5.6.1.2.2  Connections to the equipotential plane.  All equipment signal
grounds are bonded to the plane using the shortest practicable runs of No. 6
AWG stranded wire.  All connections to the plane should be welded or brazed;
where this is not feasible, adequate cable clamps may be used.  The plane is
bonded to all adjacent structural steel and is connected to the EESS at
multiple points around the perimeter of the facility using No. 1/0 AWG
stranded wires.  All equipment racks, cabinets, and cases will be grounded to
the plane using short No. 6 AWG stranded copper wires bonded to the plane and
bolted to grounding studs which are welded to each rack or cabinet.
Equipment cases are grounded through the rack/cabinet ground, or are equipped
with individual grounding conductors to the plane.  If a case ground is not
provided, a ground terminal should be installed as near the power entrance
point as possible.  Cable shields arc circumferentially bonded at both ends
to case grounds or ground buses which are connected to the plane.  Cable
ladders and ducts are grounded at each junction.  When cable ladders are
installed, a No. 6 AWG copper wire is installed on the underside of the
ladder, and all rack/cabinet grounds are bonded to the wire using
pressure-type connectors.  The ladder should be bonded to the equipotential
ground plane at the point where the bonding conductor is the shortest.  Cable
ducts carrying de power or signal/control lines will be grounded by the same
method.  Cable ducts carrying ac power will be grounded to the ac protective
ground bus in the power panel.  Practical techniques for equipotential planes
in new and existing facilities are available in FIPS PUB 94.  Other grounding
and bonding requirements are contained in Article 250, NEC.
5.6.1.3  Fault protection subsystem (FPSS).  All equipment will be equipped
with a conductor serving as the FPSS. (See NEC and MIL-STD-188-124.) The FPSS
terminates on the power ground terminal of the equipment and the ground bus
in the power panel.  If the equipment does not have a ground terminal, one
should be added to the equipment case ac, near the power entrance point of
the equipment as possible.  Extreme caution must be exercised to ensure the
phase, neutral, and FPSS conductors are not reversed.  The neutral and FPSS





 


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