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 MIL-HDBK-232A
conductors are bonded together at the first service disconnect or service
transformer, and further bonded to the EESS. This is the only intentional
grounding of the neutral conductor that is permitted by MIL-STDs or local
codes. In shielded facilities, the FPSS conductor does not penetrate the
shield. At the shield, the conductor will he bonded to the shield on the
inside and outside. No aperture is made for the conductor.
NOTE: This handbook, in consonance with MIL-STD-188-124, emphasizes that the
FPSS and power neutral conductors will be tied together only at the first
service disconnect. Some equipment has been designed with the equipment
chassis as a neutral return. Since the FPSS is also bonded to the chassis,
currents in the FPSS are possible.
5.6.1.4 Lightning protection subsystem. Where lightning protection is
required, it shall be designed using MIL-STD-188-124, MIL-HDBK-419, and the
National Fire Protection Code No. 78.
5.6.1.5 Building structural members. All steel structural members of tile
facility will be bonded together and grounded to the EESS.
5.6.2 Bonding. Bonding is the electrical connection between two metallic
surfaces established to provide a low impedance path between those surfaces.
This may be between two or more items of equipment, equipment and the
equipotential plane, or the equipotential plane and the EESS. The preferred
method of bonding is welding or brazing. This provides a strong bond which
should not be affected by intense heat created by lightning or EMP/HEMP.
Bonding may be accomplished through the use of pressure connectors (see
figure 49). Pressure connectors should be inspected frequently to ensure
adequacy of bonding. Ground conductors may be soldered if there is little
risk from surges which may cause the solder to melt. Soldering should only
be used if other methods are not feasible. Soldering is never used in the
FPSS or lightning subsystem. Ail structural steel members of the building
should be bonded together. This is done by welding all seams and joints.
The members may be bonded by installing a jumper wire constructed of No. 1/0
AWG wire and crimp-type connectors. The connectors should be welded to the
members. However, the connectors can be bolted or riveted if welding is not
feasible. If pressure connectors or rivets are used, it is important that
connections are tight, providing a strong mechanical bond. Further, such
mechanical bonds should be accessible for periodic inspection. The steel
members are connected to the EESS by using No. 1/0 AWG stranded copper wire.
The cases of all power-line filters are bonded to the facility entrance
plate. This is accomplished by circumferentially welding the case of all
filters that penetrate the facility entrance plate, and connecting a No. 1/0
AWG stranded copper wire between the filter case and facility entrance plate
if wall-mounted filters (generally power) are used. In addition to NEC
bonding requirements for building metallic networks, where the equipotential
plane is installed, all other metallic networks penetrating the plane
(air-conditioning ducts, power conduits, structural beams, etc.) or adjacent
to the plane should be bonded to the plane. Where dissimilar metals are to
be bonded, consult MIL-HDBK-419 for additional protective measures.
5.6.3 Shielding. Shielding consists of those actions taken to reduce the
coupling of electrical or magnetic fields into or out of circuits through the
use of EM barriers. The methods of shielding may vary depending upon the
type of equipment used, physical construction of the facility, and any
requirement for HEMP hardening. Cable which has a nonferrous circumferential
shield should be used for RED signal and control lines and is also
recommended for BLACK lines. The shield of all cables used within an REA,
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