What circuit integrity means
Circuit integrity is the ability of a cable to keep delivering power or a signal while it is exposed to fire. In the IEC 60331 test, a cable sample is energised at its rated voltage, mounted in a test rig and exposed to a flame. During the test the circuit is monitored: if a conductor breaks or the insulation fails so that a fuse blows or the indicator lamps go out, the test has failed at that moment. The result is the length of time the circuit survived, compared with the duration required by the product specification.
That is a different question from flame spread. IEC 60332 asks whether the cable carries fire along its length; IEC 60331 asks whether the circuit survives inside the fire. A cable can be excellent at one and poor at the other, which is why our fire-resistant vs flame-retardant guide treats them as two lines on every specification.
IEC 60331 appears most often in specifications for buildings and infrastructure outside the UK, and in export projects that follow IEC practice: fire alarm and voice alarm circuits, emergency lighting feeds, smoke extraction fans, fire pumps and lifts used for evacuation. It is also common on tender documents for tunnels, metros and hospitals, where several life safety systems share the same cable routes. In each case the specification normally states the required duration and sometimes the part, and the cable offered has to match both, with the report attached to the submittal.
The parts of IEC 60331
The standard is published in several parts, and the part on a report tells you which kind of cable and which test arrangement was used. Datasheets in the market still quote older and newer parts side by side, so it pays to read the number carefully.
| Part | Scope as commonly described | What to check |
|---|---|---|
| IEC 60331-1 | Fire with shock, cables of overall diameter above 20 mm | Flame temperature, shock arrangement, duration |
| IEC 60331-2 | Fire with shock, cables of overall diameter up to 20 mm | Flame temperature, shock arrangement, duration |
| IEC 60331-21 (1999 edition) | Older procedure, still often cited on datasheets | Edition year and whether the specification accepts it |
| IEC 60331-3 | Cables tested inside metal enclosures | Whether your installation uses enclosures |
In the parts with mechanical shock, the flame is commonly described as at least 830 degrees C and the sample is struck at intervals during the test, to reflect falling debris and vibration in a real fire. The required duration is set by the product specification rather than by the test method itself; 90 and 120 minutes are commonly specified. A report should state the part, the edition, the flame temperature, whether shock was applied, the test voltage and the time survived. These descriptions come from secondary sources, so for a formal specification check the edition of the standard named on the report with your test lab.
What the report proves, and what it does not
A pass under IEC 60331 proves that the tested sample, in that test arrangement, kept its circuit for the stated time. It does not prove three things buyers often assume.
- It does not cover the installation system. In a real building the cable hangs on clips, trays or ladders and passes through penetrations. If the supports fail first, the cable falls. In the UK, BS 8519 addresses this by referring to tests of cables with their fixings; elsewhere the project engineer decides how supports are specified. Our BS 6387 and BS 8519 guide covers the UK route.
- It does not cover every size. The report covers the constructions tested and any family grouping the standard and the laboratory allow. The desk reads the sample list on each report.
- It does not cover other fire properties. Flame spread, smoke density and acid gas are separate tests: IEC 60332, IEC 61034 and IEC 60754. In EU buildings the CPR class is declared separately on the DoP.
The construction behind the result
Most cables that pass IEC 60331 use a mica tape fire barrier directly over the conductor. Our reference construction on the fire-resistant cables page is 0.6/1 kV Cu/Mica/XLPE/LSZH 4x25 mm2: annealed copper conductor, mica tape, XLPE insulation, fillers and binder tape, and an LSZH outer sheath, with overall diameter and weight per datasheet. In the test the XLPE and sheath burn, and the mica layer keeps the conductors separated so the circuit survives.
The details of the tape matter: tape type, number of layers, overlap and tension in the taping head. A plant that changes its mica tape supplier or its taping set-up may produce a cable that looks identical and behaves differently in the furnace. That is why the desk checks, on repeat orders, whether the construction and its materials are unchanged since the report date, and records it with the drum documents. Conductor quality matters too: a fire-resistant cable with an undersized or substituted conductor is a double failure, and conductor resistance is checked per drum against IEC 60228. The mineral insulated route is covered in the mineral insulated cables guide.
Reading a circuit integrity report
- Laboratory and date: an identified laboratory, ideally accredited for the test, and a report date you can place against the plant's current production.
- Standard, part and edition: for example IEC 60331-1 or -2 with the year; check that your specification accepts that edition.
- Construction: designation, size, core count, materials and plant reference that match your spec sheet.
- Conditions: flame temperature, shock, test voltage and the time survived.
- Result wording: a clear pass for the required duration, not "no failure observed during the observation period" without a time.
When the report checks out, the claim on our pages and documents reads "circuit integrity to IEC 60331 per test report", with the report reference attached to the order. If no report exists for your exact construction, a new test adds time and cost before production; the testing and inspection page explains how the desk plans it. Typical MOQ and lead time wording for fire-performance constructions is on the MOQ and lead time page, and every order is confirmed in writing. To start, send the circuit list, required duration and sizes through the quote form.