Basic Cable Construction and History

As long as there has been electricity, there has been a need for cable to convey this power. In the late 1800's 10,000 volt concentric cables of Ferranti were installed in London, and early proved the success of underground power transmission(!).

Prior to this time insulated cable designs were limited to the manufacturing of telephone and telegraph cables for communication purposes. Paper insulation was the primary type used during the early underground cable years. 

Most often the paper insulated cables were lead or steel sheathed for mechanical and environmental protection. The demand for higher and higher rated voltages for underground cables originates from both technical and economic considerations. The transmission of power for a given voltage from a large generating station by an insulated cable is limited by the amount of current it can safely carry without overloading the insulation. This problem has resulted in reducing the current by raising the transmission voltage, allowing a smaller amount of conductor current for a given amount of power. It appears that the cost of a cable system is largely proportional to the amount of conductor metal employed and therefore to some extent inversely proportional to the voltage. It must be kept in mind however, that the saving 2 is not directly proportional to the voltage, as the higher voltage involves increased thickness of dielectric, and protective jacketing materials which partially offset the saving due to reducing the size of the conductor. The basic construction of a cable involves many processes and materials.