SHORT CIRCUIT PERFORMANCE OF METALLIC SHIELDS AND SHEATHS ON INSULATED CABLE
|Publication Date:||6 June 2017|
Equations and parameters have been established for short circuit calculations for sheaths or shields made of aluminum, bronze, copper, lead, steel, zinc and cupronickel alloys. The types of sheaths or shields included are:
• Wires, applied either helically, as braid or serving; or longitudinally with corrugations.
• Helically applied flat tape, not overlapped.
• Helically applied, overlapped, flat tape.
• Corrugated tape, longitudinally applied.
• Tubular sheath
The types of cable materials in contact with the sheath or shield are: crosslinked (thermoset), thermoplastic, impregnated paper, and varnished cloth.
The materials which determine the maximum allowable short circuit temperatures are: paper, varnished cloth and several thermoplastic and thermosetting materials presently appearing in ICEA standards. Temperature limits, considered safe, were established for the various coverings and insulation materials.
The equations may be used to determine:
• The maximum short circuit current permitted for a specific sheath/shield and short circuit duration.
• The sheath/shield size necessary to carry a specific short circuit current for a given duration.
• The maximum duration a specific sheath/shield can carry a specific short circuit current.