1.7 BONDING PRACTICES. High quality bonds between conducting elements throughout the facility are
essential ingredients to the effective functioning of all grounding and shielding networks. It is thus of
paramount importance that thorough consideration be given to bonds and bonding throughout design and
construction of a facility. A bonding resistance of 1 milliohm indicates a high quality junction has been
achieved. See Volume I, Chapter 7, for additional information.
1.7.1 Application Guidelines.
Utilize welding (exothermic) whenever possible for permanently joined bonds. The welds must be
adequate to support the mechanical load demands on the bonded members, and the following minimum
requirements must also be met:
(1) On members whose maximum dimension is 5 cm (2 inches) or less, the weld must extend
completely across the side or surface of largest dimensions.
(2) On members whose largest dimension is greater than 5 cm (2 inches) but less than 30 cm
(12 inches), one weld of at least 5 cm (2 inches) in length must be provided.
(3) On members whose largest dimension is greater than 30 cm (12 inches), two or more welds,
each not less than 5 cm (2 inches) in length, are to be provided at uniform spacings across the surface of largest
dimension. The maximum spacing between successive welds must not exceed 30 cm (12 inches).
(4) At butt joints, use complete penetration welds on all members whose thickness is 0.63 cm
(l/4 inch) or less. Where the thickness of the members is greater than 0.63 cm (l/4 inch), the depth of the weld
must not be less than 0.63 cm (l/4 inch).
(5) Fillet welds are to have an effective size equal to the thickness of the members or as specified
by Construction Specification for the Design, Fabrication, and Erection of Structural Steel for Buildings (1-7).
(6) At lap joints between members whose thickness is less than 0.63 cm (l/4-inch), double fillet
welds must be provided.
Use brazing (or silver soldering) for permanently bonding copper and brass.
Do not use soldered connections in the fault protection subsystem, the lightning protection
subsystem or the earth electrode subsystem.
All structural bolted connections must conform to the torque requirements of Table 1-23.
The proper order of assembly for bolted bonds is illustrated in Figure 1-70. Position load
distribution washers directly underneath the bolt head or under the nut next to the primary member.
Lockwashers may be placed between the nut and any load distribution washers. Toothed lockwashers should not
be placed between the primary bonded members but may be used as shown in Figure 1-70 for interior locations
that are not exposed to moisture and where electrochemically compatible metals for the washer and bond
members are utilized.