For Low-Smoke Zero-Halogen (LSZH) flame-retardant cable, the three most common flame-retardancy evaluation systems in domestic and international markets are the GB/T 31247 standard (classification of burning behavior for cables), the EU CPR (Construction Products Regulation) system, and the IEC 60332-3 standard (bunched cable burning test). What are the differences and connections between the commonly cited "Class B1" cables, "Class B1ca" bunched flame-retardant cables, and "IEC 60332-3 Class B" flame-retardant cables?
Traditional single-cable burning tests only evaluate a cable's flame-retardant capability under small-scale flame exposure, whereas fires in actual engineering projects often occur in environments where cables are installed in bunches. Consequently, mainstream international standards have evolved from single-cable burning evaluations to bunched-cable burning evaluations, and further into comprehensive fire performance evaluation systems.
For LSZH cables, it is necessary not only to control flame propagation but also to reduce smoke emission and the generation of toxic, corrosive gases, thereby enhancing personnel safety during evacuation and improving equipment protection under fire conditions.
As building fire safety regulations have become increasingly stringent, cable flame-retardancy standards have evolved from single-cable burning evaluations to bunched-cable burning evaluations, and subsequently to comprehensive fire performance evaluations.
Early flame-retardancy tests for cables primarily utilized the IEC 60332-1 and IEC 60332-2 single-cable burning tests. These tests assessed the burning behavior of individual wires or cables exposed to a small ignition source, evaluating the material's basic flame-retardant properties. However, in practical engineering applications, cables are frequently installed in bunches—such as in cable trays, conduits, or vertical shafts. In the event of a fire, flames typically spread rapidly along the bunched cables rather than along a single cable. To more realistically simulate fire environments in engineering applications, the IEC established the IEC 60332-3 standard for the bunched burning of cables.
Subsequently, as fire safety requirements for hospitals, airports, data centers, subways, and large commercial buildings became increasingly stringent, evaluating flame propagation alone was no longer sufficient to meet engineering needs. Europe established the Construction Products Regulation (CPR) framework, while China issued GB/T 31247, "Classification for burning behavior of electric and optical fiber cables," initiating the evaluation of cable fire performance across multiple dimensions, including heat release, smoke release, and corrosivity.
Consequently, the current flame-retardancy evaluation landscape for Low-Smoke Zero-Halogen (LSZH) cables is structured with IEC 60332-3 as the foundation, complemented by the higher-level evaluation systems of CPR and GB/T 31247.
IEC 60332-3 is a standard established by the International Electrotechnical Commission (IEC) for testing the bunched burning behavior of cables.
The standard evaluates the flame propagation capability of cable bunches under fire conditions by mounting a specified quantity of cables vertically on a test ladder and applying a standard flame for a fixed duration.
IEC 60332-3 comprises four categories:
| Category | Volume of non-metallic materials | Flame exposure time | Standard |
| Cat.A | 7L/m | 40min | IEC60332-3-22 |
| Cat.B | 3.5L/m | 40min | IEC60332-3-23 |
| Cat.C | 1.5L/m | 20min | IEC60332-3-24 |
| Cat.D | 0.5L/m | 20min | IEC60332-3-25 |
Among these, Cat. A has the strictest requirements, while Cat. D has the least stringent.
Currently, common low-smoke, zero-halogen (LSZH) sheath materials on the market are primarily used for Cat. C and Cat. B rated cable products. Cat. B has become a common flame-retardant requirement for building wiring, rail transit cables, data center cables, and fiber optic cables.
The core metrics of IEC 60332-3 are flame spread height and charring height; essentially, it is a flame propagation test designed to evaluate whether a cable can inhibit the spread of fire along a cable bundle.
IEC 60332-3 is used to evaluate the flame propagation characteristics of bunched cables.
During the test, a specified number of cables are secured to a vertical ladder rack, with the volume of non-metallic material determined based on the Cat. A, Cat. B, Cat. C, or Cat. D rating. A flame is then continuously applied using a ribbon-type propane burner.
Acceptance Criteria:
No continued combustion after the flame is extinguished;
Charring height must not exceed 1.5 m.
IEC 60332-3 primarily evaluates flame propagation and does not assess heat release, smoke emission, or acidic gas emissions.
CPR (Construction Products Regulation) is the EU regulatory framework for construction products, used to evaluate the fire performance of cables permanently installed in buildings.
CPR classes include: Aca, B1ca, B2ca, Cca, Dca, Eca (single-cable flame retardancy), and Fca.
Among these, B1ca and B2ca are currently the most common target classes for high-end LSZH (Low Smoke Zero Halogen) cables.
Many cable manufacturers believe that passing the IEC 60332-3 Cat. B test means the product meets CPR B2ca requirements.
In reality, the two are not directly equivalent. IEC 60332-3 primarily evaluates flame propagation, whereas the CPR system goes further by assessing the heat and smoke generated during a fire.
CPR adopts EN 50399 as its core fire test method.
During the test, the cable is mounted vertically within a large-scale fire test apparatus.
Standard heat source: Propane burner with a heat output of approximately 20.5 kW.
Test duration: 20 minutes.
CPR testing is conducted according to EN 50399, with key evaluation metrics including:
Fire Growth Rate (FIGRA)
Total Heat Release (THR)
Smoke Growth Rate (SMOGRA)
Total Smoke Production (TSP)
Flaming droplets/particles class
Acidity class
Therefore, CPR evaluates the overall hazard level of a cable in a real-world fire scenario, rather than simply whether the flame spreads. For LSZH sheath materials, passing IEC 60332-3 does not guarantee certification to the CPR B2ca or B1ca class.
GB/T 31247, "Classification for burning behavior of electric and optical cables," is a comprehensive evaluation system for the combustion performance of electric and optical cables in China. This standard applies to products such as power cables, control cables, communication cables, building wiring, and optical fiber cables.
The combustion classes under GB/T 31247 include Class A, Class B1, Class B2, and Class B3; Class B1 represents a high-performance flame-retardant cable.
Class B1 cables have become a key product choice for projects such as hospitals, airports, subways, schools, large commercial buildings, and data centers.
Unlike IEC 60332-3, GB/T 31247 evaluates not only flame spread but also: bunched cable combustion performance, heat release performance, smoke density, smoke production rate, flaming droplets, halogen acid gas emission, and gas acidity/conductivity.
GB/T 31247 is, in itself, a classification standard.
The test data is derived from various national standards and IEC standards.
Key parameters include: Bunched cable combustion
Based on: GB/T 18380.35 (equivalent to IEC 60332-3-24) or GB/T 18380.36 (equivalent to IEC 60332-3-23)
Evaluation: Flame spread height
Heat release test
Based on: GB/T 31248 (equivalent to IEC 61034 and parts of the EN 50399 system requirements)
Evaluation: Peak heat release rate, total heat release
These test results collectively determine the cable's final combustion class.
Therefore, a Class B1 cable is not merely a standard flame-retardant cable, but a product offering superior comprehensive fire safety performance.
Differences and connections between the three major standards
In terms of testing logic, there is a clear evolutionary relationship among the three. IEC 60332-3 addresses the issue of whether flame propagates rapidly along a cable bundle.
In contrast, the CPR system and GB/T 31247 further evaluate the heat release, smoke generation, formation of flaming droplets, and emission of corrosive gases during cable combustion.
Therefore:
IEC 60332-3 is a fundamental standard for evaluating bunched-cable combustion;
The CPR is a comprehensive fire performance evaluation system for construction cables;
GB/T 31247 is a comprehensive fire performance evaluation system for cables.
For LSZH (Low Smoke Zero Halogen) cables, compliance with IEC 60332-3 does not guarantee that the requirements for CPR Class B1ca or GB/T 31247 Class B1 will be met.
| Comparison of Key Test Conditions and Limits for IEC 60332-3, GB/T 31247 Class B1, and CPR EN 50575 | ||||
| Test Items | IEC 60332-3 Cat.B | GB/T 31247-B1 | CPR B2ca | CPR B1ca |
| Key criteria | IEC 60332-3-23 | GB/T 31247 | EN 50575 + EN 50399 | |
| Test Objective | flames spread | Classification of overall fire performance | ||
| Flame exposure time | 40 min | 20 min | ||
| Bunched-cable burning requirements | Charring height≤1.5 m | |||
| Fire growth rate | Exempt assessment | ≤120 W/s | ||
| Total Heat Release（1200s） | ≤15 MJ | ≤15 MJ | ≤7.5MJ | |
| Peak Heat Release Rate(PHRR) | ≤300 kW | Controlled via FIGRA | ||
| Smoke Peak Generation Rate（SPR） | ≤0.25 m²/s | Controlled via SMOGRA | ||
| Smoke Generation Rate（SMOGRA） | Exempt assessment | ≤30m²/s² | ||
| Total Smoke Yield（1200s） | ≤90 m² | ≤50 m² | ||
| Smoke Density (Light Transmittance) | ≥60% | The s1 class must meet the requirements of EN 61034. | ||
| Dripping material during combustion | Observation Record | d0 | ||
| Acidic halide gases | Exempt assessment | pH≥4.3 | ||
| Electrical conductivity | ≤10 μS/mm | ≤2.5 μS/mm（a1） | ≤2.5 μS/mm（a1） | |
| Applicable Products | Flame-retardant cable | B1 Cable | B2ca Cable | B1ca Cable |
This is one of the most common misconceptions in the industry.
Although both GB/T 31247 Class B1 and CPR Class B1ca represent high-level flame-retardant cables, they do not correspond to the exact same standard classification.
They utilize different testing standards, evaluation limits, and certification systems.
Therefore, from a standards perspective, there is no equivalence (Class B1 ≠ B1ca), nor is there an official conversion formula between them.
However, in terms of actual performance, materials meeting one standard can often pass the other.
In engineering practice, they are generally viewed as products with equivalent market positioning, yet they must undergo separate testing and certification processes.
For standard LSZH materials, achieving the IEC 60332-3 Cat.C rating is not difficult.
However, when the target is upgraded to GB/T 31247 Class B1 or CPR B1ca, the complexity of material design increases significantly.
At this level, the material must simultaneously control flame spread rate, heat release, smoke emission, flaming droplet behavior, and char formation capability. Consequently, high-performance LSZH sheath materials typically employ highly filled inorganic flame-retardant systems, combined with char-promoting and smoke-suppressing technologies, to strike a balance between flame retardancy and mechanical properties.
Such high-performance LSZH materials have become a key trend in the market for building wiring, fiber optic cables, and rail transit cables.
ANGREEN offers a range of LSZH sheath material solutions tailored to the flame-retardancy requirements of different markets.
Our products cover application needs such as IEC 60332-3 Cat.B, GB/T 31247 Class B1, and CPR B2ca, serving sectors including building wiring, power cables, rail transit cables, communication cables, and fiber optic cables.
Designed using an LSZH flame-retardant polyolefin system, these materials balance flame retardancy with mechanical properties and processing stability, allowing us to provide solutions customized to specific project requirements. Although IEC 60332-3 Category B, GB/T 31247 Class B1, and the EN 50575-CPR system are all used to evaluate the fire performance of cables, they belong to different levels of standardization frameworks.
IEC 60332-3 primarily evaluates flame propagation characteristics, whereas GB/T 31247 Class B1 and CPR Class B1ca assess a broader range of fire performance indicators, including heat release, smoke emission, flaming droplets, and corrosivity.
For building wiring, fiber optic cables, data center cables, and high-safety engineering projects, the use of LSZH (Low Smoke Zero Halogen) sheathing materials that meet the relevant standards is a crucial foundation for achieving high-level flame retardancy. As fire safety regulations continue to evolve, Class B1 cables, Class B1ca cables, and high-performance LSZH cables will see increasingly widespread application in the future.
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