b) Fault protection subsystem. NFPA 70, in Article 250, requires
that a single electrode consisting of a rod, pipe, or plate, and not having a
resistance to ground of 25 ohms or less, be augmented by additional made
c) Qualification of NFPA 70 resistance requirements. MIL-STD-
188/124A establishes a design goal, of 10 ohms for facility ground systems.
Where this is not possible, alternative methods should be considered for
reducing resistance to the lowest feasible resistance-to-ground value. For
detailed discussions and applications, refer to MIL-HDBK-419, Sections 2.6 and
2.9 of Volume I and Section 1.2 of Volume II.
d) Lightning protection subsystem. For lightning protection, a
grounding resistance of 10 ohms or less is recommended. For a detailed
discussion, refer to MIL-HDBK-419, Sections 2.6, 2.9, 3.7, and 3.8 of Volume I
and Section 1.3 of Volume II.
Specific Grounding Requirements
Electronic Equipment. Each piece of electronic equipment shall be
served by a green ground wire carried in the same cable or conduit as the
power service to the equipment.
Distribution Service: The neutral of the distribution service.
shall be grounded only at the main service entrance, at which point it shall
be grounded to the EES.
Security Fence. Permanent security fencing normally requires a
grounding system to ensure personnel safety and, in some instances, to prevent
re-radiation of signals. Grounded security fence shall be constructed of
galvanized chain-link fencing with bonded connections at all intersections, or
with a No. 8 American Wire Gage (AWG) (minimum) copper conductor woven through
the fabric of the entire length of the fence. The wire addition shall not be
substituted for the top rail of the fence. The supporting posts and top rails
shall be made of electrically conductive material. Both the fence posts and
the fence fabric or conductor wire shall be grounded by an 8-foot ground rod
at alternate fence posts. When a gate is incorporated, its hinges shall be
bonded with flexible No. 8 AWG copper wire. These wires shall be connected to
the gate post and the frame of the gate using exothermic welding or approved
pressure connectors. No fencing material shall be installed which has been
covered with non-conductive material.
General Bonding Requirements. Steel framing shall be bonded to the
facility's ground system. Vertical columns shall be bonded at the top and
bottom. Reinforcing steel shall be bonded 10 feet (3.05 m) on center each
way, unless otherwise specified. Helix houses and most LF facilities have
more stringent bonding requirements and shall be bonded according to the
criteria set forth in this manual and the project BESEP.
Specific Bonding Requirements
Cable Trays. Cable trays shall be used as part of the overall
system bonding scheme. Tray sections shall be bonded together to provide a