MIL-HDBK-1025/10
5.3.5 Temporary Grounding of Aerial Lines. Ground by installing an
overhead distribution grounding set. The grounding set provides a parallel low-level
(milliohm) resistance path that limits the current flow through the worker to a very low
(safe) value (milliamperes) thus limiting the potential across the worker to a safe value. If
the ground resistance were in series with the worker life-endangering currents could flow
through the worker under fault conditions. Avoid any ground connection that could
provide violent whipping from wind action.
a. Figure 3 shows a single-point ground. Double-point grounds are sometimes
utilized but single-point (equipotential) grounding is the preferred method. If double-point
grounding is necessary, install the temporary grounds at least one span away from the
work site because the grounding cables may violently move during a fault condition.
b. An incorrect multi-point ground is shown on Figure 4.
Figure 3
Figure 4
Correct Single-Point Ground
Incorrect Multi-Point Ground
5.3.6 Temporary Grounding of Substation Current-Carrying Equipment
Components. Ground de-energized current-carrying components of substation
equipment before approaching them within working clearance distances given in Table 11.
Grounds should be placed as close to the equipment as practical (see distance D1 on
Figure 5) to minimize the inductive voltage loop (see distance D2 on Figure 5) formed by
the ground cable and the worker. See Tables 24 and 25. Special precautions are needed
during oil handling (Table 26) to prevent the buildup of hazardous electrical charges.
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