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 MIL-HDBK-419A
1.4.5.1 Metal Conduit.
All metal conduit is to be grounded, regardless of whether it is used for enclosing power cables or
a.
for signal and control cables.
All joints between sections of conduit and between conduit, fittings and boxes should be made
b.
electrically continuous when they are installed.
c.
All pipe and locknut threads should be thoroughly cleaned before they are engaged and then
tightened firmly. For additional information see Sections 7.6 and 7.7 of Volume I.
Gouging locknuts must positively penetrate all paint or other nonconductive finishes.
d.
e.
Any joints not inherently continuous should be bonded with jumpers of No. 12 AWG or larger copper
wire. These jumpers should be welded or brazed in place or attached with clamps, split bolts, grounding
bushings, or screws and lockwashers.
Protect the bonds against weather, corrosion, and mechanical damage.
f.
Firmly tighten the screws on the cover plates of pull boxes, junction boxes, and outlet boxes.
g.
h.
All conduit brackets and hangers should be securely bonded to both the conduit and to the structural
member to which they are attached. Bond conduit runs, to include the individual sections, couplings, line
fittings, pull boxes, junction boxes, outlet boxes, etc., to the facility ground system at intervals not exceeding
15 meters (50 feet). The resistance to each connection should not exceed 5 milliohms.
1.4.5.2 Cable Trays. Make all cable tray systems electrically continuous by bonding together each individual
section as described in Section 1.7.4.1. Bond each support bracket or hanger to the cable trays which they
support. Connect the cable tray assemblies to the facility ground system with copper cables or equivalent
conforming to the 2000 cmil per foot criterion. Make the connections within two feet of each end and at
intervals not exceeding 15 meters (50 feet) along the run. Where metal covers are used, they should be securely
bolted in place.
1.4.5.3 Enclosures. Ground all enclosures of electrical and electronic wiring and distribution equipment in
accordance with MIL-STD-188-124A.
1.4.5.4 Cable Armor. The armor on electrical power cables should be bonded to the facility ground system at
each end if the cables are 3 meters (10 feet) or longer. Provide supplemental connections at intervals not
exceeding 15 meters (50 feet). The resistance of each connection should not exceed 5 milliohms.
1.4.5.5 Rotating Machinery. The frames of motors, generators, and other types of electrical rotating
machinery are to be connected to the facility ground system in accordance with the NEC requirements (l-6).
1-103
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