Single Cable Burning Test: Standards, Procedures, and Pass Criteria for Wire Flammability Evaluation

The single cable burning test is a standardized flammability evaluation that measures how an individual insulated wire or cable responds to direct flame impingement under controlled laboratory conditions. Governed primarily by IEC 60332-1-2 and its international equivalents such as EN 60332-1-2 and GB/T 18380.12, the test is essential for verifying the flame-retardant performance of cable products before they reach the market. This article explains the test principle, applicable standards, sample requirements, procedures, and common applications of the single cable burning test performed by accredited third-party laboratories and cable manufacturers worldwide.

Technical Overview

The single cable burning test, also known as the test on a single vertical insulated wire or cable, assesses the ability of an individual cable to resist flame propagation and to self-extinguish after the ignition source is removed. In this test, a specimen is mounted vertically and exposed to a calibrated gas burner flame applied at a defined angle and for defined durations. The extent of charring, afterflame behavior, and downward flame spread are then evaluated against strict acceptance criteria.

Unlike bunched cable flame tests, which simulate grouped cable installations, the single cable burning test evaluates one cable in isolation. It therefore characterizes the intrinsic flame-retardant properties of the insulation and sheathing materials and the cable construction itself, rather than the behavior of cables installed in bundles. The main international and national standards include:

• IEC 60332-1-1 and IEC 60332-1-2 — apparatus and procedure for the 1 kW premixed flame test on a single vertical insulated wire or cable
• IEC 60332-2-1 and IEC 60332-2-2 — corresponding tests for small-diameter single wires
• EN 60332 series — European adoption of the IEC methodology
• GB/T 18380 series — the Chinese national standard technically aligned with IEC 60332
• UL 1581 and UL 2556 — the VW-1 vertical wire flame test used in North American practice
• JIS C 3005 — Japanese test methods for wire and cable flammability
• ASTM D 5025 — specification of laboratory burners used in small-scale flame testing

Passing this test is also a prerequisite for certain fire classification levels of cables in several regulatory frameworks, for example as a basis for lower Euroclass ratings of construction cables in Europe.

Testing Samples

Power and Distribution Cables

Single-core and multi-core power cables with PVC, XLPE, or low smoke zero halogen (LSZH) insulation and sheathing are commonly submitted. Specimens are typically cut to a length of 600 mm ± 25 mm as required by IEC 60332-1-2, with the ends prepared and the cable surface cleaned to remove contaminants that could influence burning behavior.

Control and Instrumentation Cables

Control cables, signal cables, and instrumentation cables used in industrial plants, panels, and automation systems are tested to confirm that a single fault-induced ignition will not propagate along the cable route.

Electronic and Appliance Wiring

Internal wiring of household appliances, information technology equipment, and luminaires is frequently evaluated. For thin, small-diameter wires, the small-wire variant described in IEC 60332-2-2 is applied to prevent the specimen from being completely destroyed by an overly severe flame.

Automotive and Special Wires

Wiring harnesses for road vehicles, evaluated in conjunction with ISO 6722 requirements, as well as wires for rolling stock, marine, and aircraft applications, may be assessed using the single cable burning test or method-specific variants such as VW-1.

Testing Items

The single cable burning test evaluates the following performance characteristics:

• Flame propagation distance along the vertical specimen
• Extent of the charred or damaged portion of insulation and sheath
• Afterflame time — the duration the specimen continues to burn after flame removal
• Afterglow time — glowing combustion without flame after flaming ceases
• Self-extinguishing capability of the cable materials
• Falling of flaming droplets or debris (with cotton indicator and paper flag assessment in VW-1 testing)

Testing Methods

IEC 60332-1-2 — 1 kW Premixed Flame Test

The test is performed inside a draft-free enclosure with adequate exhaust. The specimen is clamped vertically on metallic supports positioned according to the standard. A propane-fueled premixed burner with a nominal power of approximately 1 kW is used; gas flow and air supply are set with calibrated flow meters to produce the standardized blue flame. The burner is inclined at 45 degrees to the vertical axis of the specimen so that the tip of the inner blue cone just contacts the cable surface at the specified application point.

The flame is applied for 10 seconds and then removed; once the specimen stops burning, the flame is reapplied for another 10 seconds. This cycle is repeated for a total of five applications. After the final application and extinguishing of the specimen, the damaged region is examined, and the charred portion is measured.

The specimen passes when the lower edge of the charred portion remains at least 50 mm above the upper edge of the lower support, demonstrating that the flame did not propagate significantly beyond the ignition zone.

IEC 60332-2-2 — Small Wire Test

For small single insulated wires, a reduced-energy flame from a smaller burner is applied to prevent the delicate specimen from burning through and dropping before meaningful data can be collected. The evaluation principle, vertical mounting, and measurement of the charred extent are otherwise analogous to the 1 kW test.

UL VW-1 — Vertical Wire Flame Test

In the VW-1 method described in UL 1581 and UL 2556, the specimen is mounted vertically with a strip of kraft paper flag attached near the top and surgical cotton placed beneath it. The burner is tilted at approximately 20 degrees, and the flame is applied five times for 15 seconds each. Acceptance requires that afterflame does not exceed 60 seconds after any application, the cotton is not ignited by flaming drips, and no more than 25 percent of the kraft paper flag is charred or singed.

GB/T 18380 and Other National Adoptions

GB/T 18380.12 and GB/T 18380.22 reproduce the IEC 60332-1-2 and IEC 60332-2-2 procedures for the Chinese market, while EN 60332 documents apply the same methods in Europe. Accredited third-party laboratories routinely perform all of these variants, ensuring that test reports are accepted across regulatory regimes.

Applications

Single cable burning test results support a wide range of engineering, regulatory, and commercial objectives:

• Product certification and market access, including CE marking support where EN 60332-1-2 forms the basis of a Euroclass rating for construction cables
• Factory quality control and routine verification of flame-retardant compounds during cable production
• Research and development of PVC, XLPE, polyolefin, and LSZH insulation and sheathing materials
• Procurement specifications for building wiring, industrial plants, data centers, and infrastructure projects
• Compliance demonstration for internal wiring of appliances, electronics, and lighting equipment
• Verification of flame retardancy for automotive harness wire and special-application cables
• Failure analysis when field incidents involve suspected inadequate flame-retardant performance

FAQ

What is the single cable burning test?

It is a laboratory flammability test in which a single vertically mounted wire or cable is subjected to a calibrated burner flame several times. The test determines whether the cable resists flame propagation and self-extinguishes, with acceptance based primarily on the limited extent of the charred portion.

Which standards govern the test?

The core method is defined in IEC 60332-1-2, with small-wire variants in IEC 60332-2-2. Regional equivalents include EN 60332, GB/T 18380, JIS C 3005, and the VW-1 method in UL 1581 and UL 2556. Burner quality is supported by ASTM D 5025.

What does a pass result mean?

In the IEC 60332-1-2 procedure, a pass means the charred portion did not extend beyond the permitted limit — the lower edge of the char must remain at least 50 mm above the top edge of the lower support — confirming that the flame did not spread along the cable.

How does the single cable test differ from a bunched cable test?

The single cable test evaluates one cable in free air and reflects the intrinsic flame retardancy of the product. Bunched cable tests, such as IEC 60332-3, evaluate grouped cables on a vertical ladder, where accumulated heat can cause flame spread even in individually flame-retardant cables. Both tests are usually required for a complete fire performance assessment.

How are samples prepared?

Specimens are cut to the standard length, typically 600 mm ± 25 mm for the 1 kW test, conditioned as specified, and mounted vertically on the support frame so that the burner flame contacts the surface at the prescribed position. Multiple specimens are normally tested as required by the applicable standard.

Where should the test be performed?

The test should be carried out by accredited third-party laboratories or by manufacturer laboratories with calibrated burners, flow control equipment, and controlled enclosures, so that results are reproducible and acceptable for certification purposes.