What is the difference between armoured and unarmoured cables specified in this code?

Armoured cables have a layer of steel wire or strip (Clause 10) for mechanical protection, making them suitable for direct burial. Unarmoured cables lack this protection and must be installed in conduits or cable trays.

Which code should be referred for conductor specifications?

IS 8130:1984 'Conductors for insulated electric cables and flexible cords' should be referred for conductor material, construction, and resistance.

What are the standard colours for core identification in three-core cables?

Clause 7 specifies that the cores shall be identified by colours red, yellow, and blue of the insulation.

IS 7098 Part 2

: 1985

Cross-linked polyethylene insulated PVC sheathed cables for working voltages from 3.3 kV up to and including 33 kV

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This standard specifies the requirements for cross-linked polyethylene (XLPE) insulated and PVC sheathed cables for medium and high voltage power distribution. It covers both single and three-core cables, armoured and unarmoured, for working voltages from 3.3 kV up to 33 kV. Note: This 1985 version has been superseded by the 2011 revision.

Specifies requirements for XLPE insulated, PVC sheathed cables with copper or aluminium conductors for high voltage applications (3.3 kV to 33 kV).

Quick Reference Values

Maximum continuous conductor operating temperature90 °C

Maximum conductor temperature during short circuit250 °C (for a duration up to 1 sec)

Standard voltage grades covered3.3 kV to 33 kV

AC high voltage test for 11kV (6.35/11kV) cable17 kV for 5 minutes

DC high voltage test for 11kV (6.35/11kV) cable45 kV for 15 minutes

Minimum insulation resistance constant (K-value) at 90°C1 x 10^12 Ohm.cm

Practical Notes

XLPE insulated cables have a higher current carrying capacity and short circuit rating compared to equivalent PVC insulated cables due to their higher temperature tolerance (90°C vs 70°C).

This part (Part 2) is for Medium/High Voltage (3.3kV to 33kV), while IS 7098 (Part 1) covers Low Voltage cables (up to 1.1 kV).

Strict adherence to the minimum bending radius specified in IS 10810 is crucial during installation to prevent damage to the insulation and sheath.