The single wire and cable flame test evaluates whether an individual insulated wire or cable can resist vertical flame propagation from a small ignition source and self-extinguish once the source is removed. Performed to internationally recognized methods such as IEC 60332-1-2, IEC 60332-2-2, GB/T 18380.12, GB/T 18380.13, and the UL VW-1 procedure, it is a core fire-safety requirement for cable manufacturers, certification schemes, and buyers worldwide. This article explains the test principle, sample requirements, evaluation criteria, methods, and typical applications of the single-cable vertical burn test.
Technical Overview
The single wire and cable flame test, commonly known as the single vertical burn test, is a fundamental fire-safety evaluation used to determine the flame-retardant performance of one insulated wire or cable in isolation. A specimen is mounted vertically inside a draught-free enclosure, and a calibrated propane burner flame is applied to the insulation or sheath for a defined period. The test assesses how far flame damage and charring propagate upward along the specimen, whether the specimen continues to burn after the burner is removed, and whether flaming droplets or falling particles ignite indicator materials placed below the sample.
The most widely applied methods are the IEC 60332 series — specifically IEC 60332-1-2 for a 1 kW pre-mixed propane burner and IEC 60332-2-2 for a reduced 500 W burner intended for thin wires. These procedures are adopted in Europe as EN 60332-1-2 and EN 60332-2-2, and in China as GB/T 18380.12 and GB/T 18380.13. In North American practice, the equivalent single-wire assessment is the VW-1 vertical wire flame test described in UL 1581 and UL 2556, while Japanese specifications reference JIS C 3005. It should be emphasized that single-cable test results describe the behavior of one cable alone; they do not represent the fire performance of cables installed in bundles, which is assessed separately by bunched-cable tests such as IEC 60332-3.
Testing Samples
The test is applicable to a broad range of single insulated conductors and finished cables. Typical sample categories are described below.
Single Insulated Wires
Building wires, hook-up and equipment wires, and other single conductors with one layer of insulation are the most common specimens. The complete construction, including the conductor and insulation as delivered, is tested without removing any component.
Power, Control and Instrumentation Cables
Single-core and multicore power, control, and instrumentation cables are tested as complete constructions, including inner coverings, fillers, armour, and outer sheaths, so that the test reflects the real fire behavior of the finished product.
Flexible Cords and Thin Wires
Small-diameter flexible cords and fine-wire products are typically evaluated with the lower-energy 500 W burner method (IEC 60332-2-2 / GB/T 18380.13), which applies a gentler flame appropriate to thin insulation walls.
Optical Fibre and Communication Cables
The IEC 60332 series covers both electric cables and optical fibre cables, so optical fibre units, data cables, and communication cables with polymeric sheaths can also be assessed using the same vertical flame apparatus.
Sample Preparation and Conditioning
Unless otherwise specified by the product standard, specimens are cut to a length of approximately 600 mm ± 25 mm, straightened, and cleaned of surface contamination. Specimens are normally conditioned for a minimum of 16 hours at standard laboratory temperature before testing, and the number of specimens per construction is defined by the relevant product specification.
Testing Items
During the single wire and cable flame test, the laboratory observes, measures, and reports the following items:
- Extent of charring or thermal damage along the specimen, measured relative to the lower edge of the top support
- Afterflame time, meaning the duration of continued flaming after removal of the burner
- Afterglow behavior, meaning glowing combustion without a visible flame
- Production of flaming or glowing droplets and particles, and whether they ignite the kraft paper or cotton indicators positioned beneath the specimen
- Stability of the insulation and sheath, including any retreat, melting, or falling away of material during exposure
- Full test parameters, including the standard applied, burner power, flame application time, and any deviations, recorded in the final test report
The pass or fail verdict is determined by comparing these observations against the acceptance criteria of the invoked standard and any additional requirements of the product specification.
Testing Methods
All single-cable flame tests share the same basic arrangement: a vertical specimen suspended in a metal enclosure that shields it from draughts, a calibrated propane gas burner producing a blue flame with a well-defined luminous inner cone, and indicator materials positioned below the specimen. Burner output is verified periodically against the calibration requirements of the applicable standard, and testing is carried out with mechanical ventilation switched off to ensure a still atmosphere.
IEC 60332-1-2 / EN 60332-1-2 / GB/T 18380.12 — 1 kW Premixed Propane Burner Method
A specimen of 600 mm ± 25 mm is clamped vertically with its upper end fixed to the top support and its lower end secured so the sample remains straight. The 1 kW pre-mixed propane burner flame is applied to the surface of the specimen so that the inner blue cone impinges on the designated contact point. The flame application time depends on the overall diameter of the specimen: 60 s ± 2 s for specimens up to and including 25 mm, and 120 s ± 2 s for specimens exceeding 25 mm. The principal acceptance criterion is that the uppermost limit of the charred or affected portion must remain at least 50 mm below the lower edge of the top support. Ignition of the kraft paper indicator by flaming droplets is recorded and evaluated as specified by the standard and the product specification.
IEC 60332-2-2 / EN 60332-2-2 / GB/T 18380.13 — 500 W Method for Thin Wires
This method uses a reduced 500 W pre-mixed propane burner suitable for small insulated wires and thin flexible cords for which the 1 kW flame would be excessively severe. The vertical specimen arrangement, indicator placement, and measurement principles are the same as in the 1 kW method, with the flame exposure duration and any additional criteria defined by the standard. The same 50 mm minimum undamaged distance below the top support is applied when judging flame propagation.
UL 1581 / UL 2556 — VW-1 Vertical Wire Flame Test
The VW-1 test is the North American single-wire flame procedure widely referenced for appliance wiring material, electronic equipment wire, and hook-up wire. A vertical specimen is exposed to a series of 15-second applications from a Tirrill-type burner, typically four consecutive applications as detailed in the standard. A kraft paper flag is attached to the specimen and a layer of surgical cotton is placed beneath it. Typical acceptance criteria require that the afterflame does not exceed 60 seconds after each application, that flaming drops do not ignite the cotton, and that the paper flag is not ignited or excessively charred beyond the limit defined in the specification.
General Test Procedure
- Condition the specimens and mark the flame application point
- Mount the specimen vertically in the draught-free enclosure with the paper or cotton indicators in place
- Verify the burner flame calibration before commencing the test series
- Apply the burner flame at the marked point for the duration specified by the standard
- Observe and record afterflame, afterglow, dripping behavior, and any ignition of the indicators
- After cooling, remove loose carbonized deposits and measure the extent of the undamaged portion
- Evaluate the results against the acceptance criteria and issue the test report
Applications
Single wire and cable flame test results are used throughout the wire and cable industry for design, compliance, and procurement purposes. Key application scenarios include:
- Material and construction development, including the formulation of flame-retardant PVC, cross-linked polyethylene, and low smoke halogen-free compounds
- Factory quality control and routine verification of flame-retardant performance during batch production
- Product certification and market access, since harmonized cable systems, national certification schemes, and listing programs for North America all reference single-cable flame requirements
- Compliance demonstration for building wiring, shipboard installations covered by IEC 60092 series requirements, rail transit projects, and utility procurement specifications
- Buyer acceptance and supplier qualification, where purchasers require test reports from ISO/IEC 17025-accredited third-party laboratories or manufacturer laboratories as contractual evidence of flame retardance
FAQ
What is the difference between the single-cable test and the bunched-cable test?
The single-cable test (IEC 60332-1-2 or IEC 60332-2-2) evaluates one wire or cable in isolation with a small burner flame, whereas the bunched-cable test (IEC 60332-3) evaluates a bundle of cables mounted vertically on a ladder with a much larger ignition source. A cable that passes the single-cable test may not pass the bunched test, so the appropriate method must be selected based on the intended installation condition.
Why do flame application times differ in IEC 60332-1-2?
The exposure duration is scaled to the thermal mass of the specimen. Specimens with an overall diameter up to and including 25 mm receive a 60-second flame application, while larger specimens receive 120 seconds, because thicker constructions require longer exposure to produce a meaningful assessment of vertical flame propagation.
What does it mean when a cable is described as passing IEC 60332-1?
It means that a representative specimen of that cable, tested vertically with the specified propane burner, met the acceptance criteria — in particular that the charred or damaged portion remained at least 50 mm below the top support and that no disqualifying ignition of indicators occurred. This designation is widely used as a baseline flame-retardant claim for individual cables.
Does passing the single-cable test qualify a cable for grouped installation?
No. The single-cable test only demonstrates resistance to flame propagation by one cable alone. Where cables are installed in groups, on trays, or in risers, specifications normally require additional evidence such as bunched-cable test results (IEC 60332-3) or broader fire-performance classifications covering smoke emission, acidic gas generation, and heat release.
Where can single wire and cable flame tests be performed?
The tests can be performed by manufacturer laboratories, certification bodies, and ISO/IEC 17025-accredited third-party laboratories equipped with the standardized vertical burn enclosure, calibrated propane burner, and indicator apparatus specified in IEC 60332, EN 60332, GB/T 18380, UL 1581, UL 2556, or JIS C 3005 procedures.