| Full title | Tests for electric cables under fire conditions. Circuit integrity (series title) |
| Publisher | IEC (TC 20, Electric cables) |
| Current parts | IEC 60331-1:2018, IEC 60331-2:2018 and IEC 60331-3:2018, all edition 2.0, published 28 March 2018 |
| Status | Parts 1, 2 and 3 current (stability date 2026). Parts 11, 21, 23 and 25 withdrawn on 31 December 2024 |
| European adoption | EN IEC 60331-1:2019 (identical to IEC 60331-1:2018) |
| Related standards | BS EN 50200, BS 8434-2, BS 8491, EN 13501-3 |
What it covers
IEC 60331 sets out test methods for cables that are required to maintain circuit integrity in a fire. Circuit integrity means the cable keeps working as intended while it is exposed to a specified flame for a specified time under specified conditions.
The current parts apply to cables of rated voltage up to and including 0.6/1.0 kV, including cables rated below 80 V, metallic data and telecom cables, and optical fibre cables. With agreement between manufacturer and purchaser, the method can be used for cables up to 1.8/3 (3.3) kV, provided suitable fuses are used.
The detailed point of failure, continuity checking, sample, procedure and test report are given only for electric power and control cables. The parts do not give these details for metallic data, telecom or optical fibre cables.
Parts of the series
| Part | Subject | Status |
|---|---|---|
| IEC 60331-1:2018 | Fire with shock at a temperature of at least 830 °C, cables up to 0.6/1.0 kV with overall diameter exceeding 20 mm | Current, edition 2.0 |
| IEC 60331-2:2018 | Fire with shock at a temperature of at least 830 °C, cables up to 0.6/1.0 kV with overall diameter not exceeding 20 mm | Current, edition 2.0 |
| IEC 60331-3:2018 | Fire with shock at a temperature of at least 830 °C, cables up to 0.6/1.0 kV tested in a metal enclosure | Current, edition 2.0 |
| IEC 60331-11:1999 | Apparatus. Fire alone at a flame temperature of at least 750 °C | Withdrawn 31 Dec 2024 |
| IEC 60331-21:1999 | Procedures and requirements. Cables up to 0.6/1.0 kV | Withdrawn 31 Dec 2024 |
| IEC 60331-23:1999 | Procedures and requirements. Electric data cables | Withdrawn 31 Dec 2024 |
| IEC 60331-25:1999 | Procedures and requirements. Optical fibre cables | Withdrawn 31 Dec 2024 |
Parts 21, 23 and 25 were fire-only tests at a flame temperature of at least 750 °C, using the Part 11 apparatus. The 2018 editions already noted that Parts 11, 21, 23 and 25 were no longer maintained and that Parts 1 and 2 are the recommended test procedures.
Part 3 covers cables tested inside a metal enclosure, for cables up to 20 mm overall diameter. Passing Part 3 does not mean a cable also meets Part 1 or Part 2.
The test in outline
- In Part 1 the sample is mounted on a steel test ladder, in Part 2 on a test wall, and in Part 3 inside a metal enclosure. It is exposed to a burner flame of at least 830 °C, while a shock-producing device applies mechanical shock.
- The power and control cable sample is energised during the test, using fuses and a continuity checking arrangement.
- Part 2 (clause 4) requires a draught-free chamber of at least 20 m³, at 10 °C to 40 °C at the start of each test.
- Mass flow meters or controllers are required to control the propane and air supply to the burner.
- In Parts 1 and 2, Annex A gives the method for verifying the burner and control system.
- The flame application time and the acceptance criteria are set out in Clause 8 of each part.
Parts 1 and 2 include requirements for an optional marking on the cable to show compliance.
What changed in the 2018 editions
- Scope extended to include metallic data and telecom cables and optical fibre cables, without detailed test procedures for them.
- Better description of the test environment.
- Mass flow meters or controllers made mandatory for fuel and air.
- Part 1: two extra vertical elements on the steel test ladder, for single-core cables without a concentric metal layer and for cables with a normal-use bending radius above about 400 mm.
- Part 2: improved figure showing sample mounting and bending radius.
- Clearer test report requirements.
How it relates to other standards
| Standard | Relationship |
|---|---|
| BS EN 50200 | European test for unprotected small cables (up to 20 mm) for emergency circuits, with flame and shock. Used for PH classification under EN 13501-3 |
| BS 8434-2 | UK method that modifies BS EN 50200 to use a 930 °C flame and water spray |
| BS 8491 | UK method for large-diameter power cables (above 20 mm) for smoke and heat control and certain other active fire safety systems |
| IEC 60332 series | Flame propagation tests. These test whether a cable spreads fire, not whether it keeps working |
What it means in practice
- Check which part and which edition a datasheet claims. A claim of IEC 60331-21 or -23 refers to the older 750 °C fire-only method, now withdrawn.
- Check the stated survival time and the conditions it was achieved under, not just the part number.
- For data and fibre cables, the IEC 60331 parts give no detailed procedure, so look for the product standard or test report that defines how continuity was monitored.
- Circuit integrity is a different property from flame retardance or low smoke.
Related reading: What is LSZH cable and when do you need it?.