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 MIL-HDBK-419A
CHAPTER 3
DESIGN CRITERIA
3.1 INTRODUCTION.
This chapter presents recommended grounding, bonding, and shielding practices for use in equipment design and
construction at levels of implementation ranging from circuit board design to installation in the cabinets. Also
presented is a set of inspection and test procedures for verifying that proper grounding, bonding, and shielding
practices have been employed in the design and construction of the equipment. The design of the equipment
should emphasize careful grounding, bonding, and shielding along with other interference and noise control
measures in order to achieve compatible operation within the electronic system in which it is installed. This
emphasis must continue to be maintained during the manufacture, installation, and operation of the equipment
or system. For example, during manufacture, careful attention should be given to the routing of cables, the
choice and mounting of cable connectors, the selection of signal and ground conductors, the correct
implementation of all bonds within the equipment, etc. When the piece of equipment is installed, the
configuration of the facility ground networks (for a detailed description of these networks, see Section 1.5) and
the integrity of the shields within the facility must be maintained. Correspondingly, the ground networks and
shields in the facility should not be allowed to degrade during the operation of equipments. For example,
ground connections should not be randomly changed in efforts to improve equipment operation without
considering what effect such changes will have on the overall system. This recommendation applies to changes
internal to the equipment as strongly as it applies to changes made external to the equipment.
Basic personnel protection measures should also be incorporated. Inadvertent contact with metal parts
operating at hazardous voltages must be prevented. Likewise, exposure to harmful emissions of either the
ionizing or nonionizing type must be avoided by the provision of appropriate shields or barriers. In addition,
protection must be provided against internal power line faults through the installation of grounding conductors
of adequate size and the incorporation of appropriately sized fuses or circuit breakers into the design.
Overvoltage and overcurrent protection should be provided on power lines, signal lines, and control lines. A
variety of measures may be used singly or in combination to provide the needed protection. Efficient
grounding, bonding, and shielding in accordance with the recommendations set forth in the following sections
are important factors in the achievement of this protection.
3.2 GROUNDING PROCEDURES.
3.2.1 Signal Grounds.
Grounding in equipment must be given the same careful attention as is given to amplifier design, filter
selection, component selection, and mechanical layout. In equipment, the signal grounding philosophy presented
in Volume I, Chapter 5 and the practices recommended in Chapter 1 of this volume for facilities are to be
applied on a smaller scale. The grounding techniques and practices used in the design of the equipment must
ensure that the signal reference points or planes internal to the equipment can be properly interfaced with
those of other equipments and those of the facility as a whole without compromising the signal ground system
of either the individual unit or the total system.
3-1
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