The tops of all towers are connected by two wires. These are the ground wires, surge arrestors that protect the line. The electric field in the conductors induces a current in the ground wires, and Hydro-Qu bec uses this induced current to supply the telecommunications stations close to the lines. The technology for extracting induced currents in ground wires was exported to Peru to supply small mountain villages close to transmission lines. Because there are so many transmission lines, there is also a variety of towers.
Some varieties have specific functions, others record the stages of technological progress.
The role of some towers is to support the conductors along straight stretches of line. These towers require 22 tonnes of steel for each kilometre of line. While the James Bay transmission system was being built, a technological breakthrough was made. The cross rope suspension tower was developed, a tower that requires only 8.7 tonnes of steel per kilometer of line. This is why three of the five transmission lines are supported by guyed-V towers and the other two by cross rope suspension towers.