Reaffirmed 2024

1. SCOPE

1.1 This standard covers the recommendation of shortcircuit temperature limits, method of calculation of short-circuit current and cross-sectional areas of components of electric cable for carrying short-circuit current for electric cables with rated voltage from

1.1 kV to 220 kV.

1.2 The following four aspects are to be considered when deciding the short circuit ratings of cable system:

a) The permissible maximum temperature limits for cable components (for example. conductor, insulation, screen or metallic sheath, bedding, armour and sheaths), for the range of voltages covered by this standard, dielectric integrity is a major limitation. For practical purposes, the energy producing the temperature rise is usually expressed by an equivalent (l2t) value so that the permitted maximum duration for a given short-circuit current can be calculated;

b) The maximum value of current which shall not cause mechanical failure (such as bursting) due to electromagnetic forces. Irrespective of any temperature limitations, this determines a maximum current which should not be exceeded;

c) The thermal performance of joints and terminations at the limits of current and duration specified for the associated cable. Accessories should also withstand the thermomechanical and electromagnetic forces produced by the short-circuit current in the cable; and

d) The influence of installation conditions on the above three aspects.

Aspect (a) is dealt within detail in this standard and the limits given are based on a consideration of the cable only. A single short-circuit application is not expected to produce any significant damage to the cable, but repeated short-circuits may cause cumulative damage. Guidance is given, where appropriate, on aspects (c) and (d), mainly as they concern thermomechanical forces in the conductors and metallic sheath. Aspect (b) is not covered in this standard.

1.3 The limits recommended in this standard should be used for guidance only. There is little scientific evidence available on the behaviour of actual cables under short-circuit conditions, most of the information being based on the tests on the constituent material themselves. It has been necessary to exercize considerable judgement in setting these recommended limits, and in general, especially for the dielectric, the best average of present usage has been suggested.

1.4 It is not possible to provide complete limits for joints and terminations because their construction is not standardized and performance varies. Where the full short-circuit capability of the cable is needed the accessories should be designed appropriately, but this is not always economically justified and the shortcircuit capability of a cable system may be determined by the performance of its joints and terminations. Where possible, guidance has been included on the performance of accessories when they are installed on cables subject to the short-circuit limits given in this standard.

2. REFERENCES

The standards given below contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standard indicated below:

692 : 1994 Paper insulated lead-sheathed cables for rated voltage upto and including 33 kv specification

1554 PVC insulated (heavy duty) electric cables:

(Part 1) : 1988 For working voltages up to and including 1 100 V

(Part 2) : 1988 For working voltages from 3.3 kV upto and including 11 kV

1885 (Part 32) : 1993/IEC 50-461 : 1984 Electrotechnical vocabulary: Part 32 Electric cables

7098 Crosslinked polyethylene insulated PVC sheathed cables

(Part 1) : 1988 For working voltage upto and including 1 100 V

(Part 2) : 2011 For working voltages from 3.3 kV up to and Including 33 kV

(Part 3) : 1993 For working voltages from 66 kV upto and including 220 kV

9968 Elastomer insulated cables

(Part 1) : 1988 For working voltages upto and including 1 100 V

(Part 2) : 2002 For working voltages from 3.3 kV up to and Including 3 3kV

14255 : 1995 Aerial bunched cables for working voltages up to and including 1100 V — Specification

14494 : 1998 Elastomer insultated flexible cables for use in mines