IEEE Std 575-2014 pdf download – IEEE Guide for Bonding Shields and Sheaths of Single-Conductor Power Cables Rated 5 kV through 500 kV.
4. Background Single conductor medium- and high-voltage power cables employ a coaxial design essentially consisting of a metallic center conductor surrounded by insulation and an outer metallic shield or sheath (outer conductor). Semiconducting layers are provided at the interface between the conductor and the insulation, and between the insulation and the metallic shield or sheath in order to provide a smooth electrical interface for the insulation and thus establish a uniform electrical stress pattern within the insulation. Cable core conductors are normally comprised of aluminum or copper wires but can be of solid construction. Present day cable insulation materials generally consist of impregnated paper, ethylene propylene rubber (EPR), or cross-linked polyethylene (XLPE). The cables are constructed with an outer metallic shield or sheath, which is primarily comprised of one of the following:   Concentrically applied copper wires, aluminum wires, or helically applied copper tapes  Extruded lead or aluminum sheathes   Longitudinally applied corrugated copper tapes sealed at the overlap   Longitudinally applied thin copper or aluminum foil laminates sealed at the overlap   Combination of wires with any of the above copper tapes NOTE—Since this document deals primarily with the electrical aspects of shields and sheaths, and to simplify the discussion, the cable metallic shields or sheaths will be referred to interchangeably as the shield or sheath unless otherwise indicated. Covering the metallic shield/sheath is normally an insulating jacket typically consisting of extruded polyethylene (PE) or comparable electrically insulating jacketing material, which protects the underlying metallic shield/sheath from electrolysis.
Safety and cost considerations often do not justify application of special bonding for cable operation below transmission voltage class. Many distribution cable installations are also multipoint grounded because they are installed in random lay with communication cables and the installations are governed by Accredited Standards Committee C2-2012, National Electrical Safety Code ® (NESC ® ) [B1] Rule 354D. 7 Conversely, on higher voltage power cable systems that carry large bulk of power, it is often economical and practical to employ special bonding in order to limit shield/sheath losses and thus maximize loading capability. For distribution class cables, the metallic shield is for the most part normally installed multipoint solidly grounded. This is due to safety concerns associated with making sure that all shield components of a specially bounded distribution cable would remain effectively insulated in the field after installation/during operation. The initial installation cost and additional maintenance associated with specially bonded installations makes this option often also less economically attractive for distribution class feeders, which have relatively lower power transfer requirements as compared to their transmission class counterpart. Thus special bonding techniques may be justified in some instances on distribution class feeders once safety aspects have been adequately addressed and the additional initial installation and subsequent maintenance costs have been effectively considered.