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 (a) Thermosetting Compounds:
o
Cross-Linked polyethylene (XLP or XLPE).
o
Ethylene propylene rubber (EPR).
o
Styrene butadiene rubber (SBR).
o
Silicone rubber.
o
Oil-base rubber.
o
Chlorosulfonated polyethylene rubber (CPR).
o
Butyl rubber.
(b) Thermoplastic Compounds:
o
Polyethylene (natural).
o
Polyvinyl chloride (PVC).
(c) Paper-laminated Tapes.
(d) Varnished Cloth-laminated Tapes.
2.2.3 Shielding of Higher Voltage Cable. For operating voltages below 2 kV, nonshielded
constructions are normally used. Insulation shielding is required for all nonmetallic, sheathed,
single-conductor cables operating above 2 kV and all metallic sheathed cables and
multiconductor cables above 5 kV.
2.2.3.1 Procedure. Shielding is the practice of confining the electric field of the cable to
the insulation surrounding the conductor by means of conducting or semiconducting layers,
closely fitting or bonded to the inner and outer surfaces of the insulation. In other words, the
outer shield confines the electric field to the space between conductor and shield. The inner or
strand stress relief layer is at or near the conductor potential. The outer or insulation shield is
designed to carry the charging currents and in many cases fault currents.
2.2.3.2 Purpose. Insulation shields have several purposes:
(a) Confine the electric field within the cable.
(b) Equalize voltage stress within the insulation, minimizing surface discharges.
(c) Protect cable from induced potentials.
(d) Limit electromagnetic or electrostatic interference (radio, TV, etc.).
(e) Reduce shock hazard (when properly grounded).
2-3
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