Quantcast Bonds and Bonding - hdbk419a_vol20229

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MIL-HDBK-419A
2.2.2.2.2 Bonds and Bonding.
a.
Visually check a representative number (5 to 10 percent) of the various types of bonds in use
throughout the facility.  An examination of one bond is not sufficient; it will not normally be necessary,
however, to examine every joint in the facility. Typical bond deficiencies to look for are illustrated in Figures
2-6 and 2-7. Other things to look for are:
(1)  Welded, brazed, or silver soldered connections should be examined for broken or cracked
seams, presence of voids, size of filler deposit (see Section 1.8.1), length and number of deposits (if
discontinuous), and evidence of corrosion.
(2)  Soft soldered bonds should be inspected for broken connections, evidence of cold solder joints
(crystalline, grainy appearance), and signs of overheating.  Soft solder should only be used to improve
conductivity at load bearing joints; it should not be required to provide mechanical restraint. There shall be no
solder joints in either the fault protection subsystem (this includes the green wire network) or in the lightning
protection subsystem.
(3)  Bolted joints should be checked for looseness, inadequately sized fasteners, corrosion of either
the fastener or main member, improper use of washers and locknuts, absence of or inadequate coverage with
protective coatings, damaged or missing hardware, and improperly cleaned mating surfaces. Be particularly
thorough in the inspection of bolted connections in areas open or exposed to the weather.
(4) Joints using rivets, clamps, and other type fasteners should generally be examined for
looseness and corrosion.
b.
Note the location and nature of specific bond deficiencies in Section B, Part II, of the Survey Form.
c.
Concurrently with or following the visual inspection of the bonds, perform bond resistance
measurements using the test procedure described in Section 2.2.2.3.1. Select five to ten bonds that visually
appear tight, well made, and corrosion free and measure their resistances.  The sampling should include
structural bonds, equipment-to-structure bonds, connections between safety ground wires, conduit-to-conduit
or conduit-to-cabinet joints, bonds in lightning down conductors (to include structural columns if used for
lightning discharge paths), and others as appropriate. Also measure all bonds exhibiting visible defects. These
measurements indicate the actual resistance between the two measurement points and also include the effects
of any paths in parallel with the bond under test.
d.
For every bond exhibiting a resistance greater than one milliohm, check for looseness; if the
connection is loose, tighten the fastener. Measure the resistance again after tightening. If the resistance is
still greater than one milliohm and the joint can be readily disassembled, disassemble the joint and check for
corrosion, debris, paint, or other nonconductive materials. Remove the material, reassemble the bond, and
remeasure the resistance. If the resistance is still greater than one milliohm, note on the Survey Form the
location of the bond and indicate the type of corrective action needed.
e.
Bonding jumpers using wires, cables, or wide metal straps are frequently used for fault grounding,
signal grounding, and lightning grounding. Fault protection jumpers should conform to Article 250 of the NEC.
If they do not conform to Article 250, the jumpers should be replaced with cables or straps of the sizes
specified by the NEC. Signal grounding straps should be only as long as needed to bridge the physical distance
and should exhibit a length to width ratio of not greater than 5 to 1. Lightning bonds should be restricted to not
more than 1.8 meters (6 feet) and should only be used to interconnect lightning down conductors to nearby
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