The use of a bond wire between the negative bus of a trolley substation and underground plant, such as a lead sheath telephone cable, to prevent anodic corrosion of the underground structure, has been recognized practice for many years.
With a single substation and track system, the potentials of underground structures near the substation are positive to the negative bus, since the current delivered to the tracks by trolleys at distant points divides among the tracks, the earth in which they are imbedded, and paralleling metallic structures in the ground, and returns to the negative bus or substation generators through the rails near the substation and the substation ground. Under these conditions, a bond wire between the negative bus and the underground cable always will carry current to the bus and provide protection to the cable.
However, when two or more substations are connected to the same track and trolley...
