Page 184 - Electromechanical Devices and Components Illustrated Sourcebook

146 Electromechanical Devices & Components Illustrated Sourcebook

outside and adjacent to the ground wire. In these cases the
ground wire operates as an arc path and not necessarily as a
conductor. If the wire is laid directly on a wooden surface, as
shown in Figure 8-41, the arc can create a flash fire and the Lightning Strike
protection that the rod provides is principally negated. Notice
that the arc path in the illustration is partly within the wooden
structure. Figure 8-42 shows the proper placement of the Lightning Rod
ground wire. Notice that the arc path is isolated from the
structure.

Cone of Protection

Ceramic
Insulator
Lightning Strike
Ceramic Stand-Offs

Lightning Rod

Arc Path
Timber Structure
Ground Wire

Cone of Protection
Figure 8-42 Correct Placement of Ground Wire and Rod

Arc Path

Power Conductor
Terminals
Arc Gap Ground Electrode
Timber
Structure Insulator

Figure 8-41 Incorrect Placement of Ground Wire

Grounded Base
Figure 8-43 Lightning Arrestor

Lightning Arrestor

For large power distribution systems lightning strikes are a
constant problem. On the occasion that lightning strikes a
conductor, a larger portion of the energy can be controlled by Protecting transmission lines is accomplished by running a
using a lightning arrestor. Figure 8-43 shows a typical power top ground wire, as shown in Figure 8-44. The top wire is
transmission lightning arrestor. The power line is placed in placed high enough to provide a cone of protection that
close proximity to a parallel ground electrode. If lightning encompasses the transmission lines. In some cases two top
strikes the power line, it will arc to the ground electrode and wires may be used. The top wire is connected to an earth
the damage can be greatly diminished. ground at every pole.