Prysmian explains fire ratings for cable

Australian cable manufacturers and suppliers routinely receive requests for cables which must be “fire rated” or “fire resistant”. Within the context of these generic descriptions there is a myriad of performance tests in use around the world with which to qualify a cable to such requirements.
In Australia and New Zealand the performance test standard relating to fire rating of cables is, AS/NZS 3013 - Electrical installations — Classification of the fire and mechanical performance of wiring system elements, specifically appendices A, B, D & E of this standard relate to the testing of cables forming a wiring system.
This standard is referenced in both the Building Code of Australia and AS/NZS 3000 - The wiring rules.
Wiring System Classifications – Deciphering the WS Code
When a cable type is assigned a wiring system code it means that a cable, representative of its group as defined by AS/NZS 3013, has satisfied the test criteria for that rating.
In order to understand what a WS rating means, reference to section 3 of AS/NZS 3013 is recommended, however the table below gives a brief overview of how the WS ratings relate to the electrical and mechanical performance of fire rated cables and elements in both normal service and fire conditions.
WS |
1st
Numeral Electrical
performance |
2nd
Numeral Mechanical
performance |
Supplementary
letter | ||
Number |
Level
of circuit integrity in fire condition |
Number |
Level
of protection against mechanical damage |
Water
spray test applied | |
Characteristic
lettering "WS" |
1 |
15
min |
1 |
Light |
The
letter "W" shall be applied as appropriate |
2 |
30
min |
2 |
Moderate | ||
3 |
60
min |
3 |
Heavy | ||
4 |
90
min |
4 |
Very
heavy | ||
5 |
120min |
5 |
Extremely
heavy |
As an example a WS52W rated cable will have the following characteristics;
- WS – be suitable for inclusion in a wiring system
- 5 - have electrical performance (circuit integrity) for 120 minutes (two hours) in a fire condition
- 2 - provide a moderate level of protection against impact damage during normal service
- W – have electrical performance (circuit integrity) following exposure to water from overhead sprinklers
Generally the level of mechanical performance (2nd numeral) offered by polymeric insulated and sheathed cables is 2 (moderate impact). This level of compliance can be met by most Australian fire rated power and control cables using standard constructional parameters from the relevant build standard(s).This mechanical performance rating can be improved to WS X3 which provides a level of medium impact against damage from vehicles such as cars and light commercial vehicles by:
- addition of 1.6mm sheet steel coverage with a maximum unsupported span of 100mm
- galvanised medium tube to AS1074
In cables of smaller conductor cross sectional areas (CSA) such as data and instrumentation cables or where higher levels of impact protection are required, utilisation of protective coverings as detailed in appendix F of AS/NZS 3013 – guide to use of the classification system, should be considered by the installer.
AS/NZS 3000 – The wiring rules contains an informative section which can be found in Appendix H – WS classification of wiring systems. This section gives guidance with regard to designation, application and mechanical protection classifications that result in compliant installations and suitable alternatives.

International Standards
The most common international standard relating to fire performance referenced by specifying engineers is;
IEC 60331 – Tests for electric cables under fire conditions – circuit integrity
- Part 21 - Procedures and requirements – cables of rated voltage up to and including 0.6/1.0 kV &
- Part 23 - Procedures and requirements – electric data cables

In the main, these standards are referenced in relation to installations where international cable build standards such as IEC are being considered and assessment of their suitability to the building code of Australia lies with the specifying engineer.