Fire-resistant and non-gorenje cable: what is the fundamental difference?

Short Answer: FR and ng Are Different Properties

ng (non-flame propagating) and FR (fire-resistant) answer two different questions. ng — will the flame spread along a bundle of cables after the ignition source is removed. FR — will the cable maintain operability while in a flame. A cable with the ng index may char and stop transmitting signal. A cable with the FR index continues to operate for a specified time, even when everything around it is burning.

In practice this means: for ordinary power lines, where the cable is not obliged to operate during a fire, the ng version is sufficient. For fire protection systems — fire alarms, emergency lighting, smoke extraction — FR is required. Replacing FR with ng is not allowed: non-propagation of combustion does not provide maintenance of operability. Replacing ng with FR is technically possible, but it is economically unjustified for lines that are not obliged to operate during a fire.

The classification is established by GOST 31565-2012 “Cable products. Fire safety requirements”, in force in Kazakhstan since 01.01.2014, with an amendment of 29.09.2025. Both properties are confirmed by different tests: ng — for flame propagation along a bundle of cables, FR — for maintaining operability in a flame.

What the Marking Means

The letter indices in the cable marking are not marketing designations, but the result of classification according to specific fire hazard indicators. Each index corresponds to a property tested by a separate method.

ng (non-flame propagating) — the cable does not propagate combustion in grouped installation. The category is indicated in brackets: A F/R, A, B, C or D. Category A is the most stringent, D the least stringent. The higher the category, the lower the volume of combustible load at which the cable retains non-propagation of combustion. Category A F/R is tested according to GOST IEC 60332-3-21 at a volume of non-metallic elements of 7 l/m, category A — according to GOST IEC 60332-3-22 at the same volume, category B — according to GOST IEC 60332-3-23 at 3.5 l/m, category C — according to GOST IEC 60332-3-24 at 1.5 l/m, category D — according to GOST IEC 60332-3-25 at 0.5 l/m.

FR (Fire Resistance) — fire resistance. The cable maintains operability when exposed to flame for a specified time: from 30 to 180 minutes. Tests are carried out according to GOST IEC 60331-2-2021 for cables for rated voltages up to 0.6/1.0 kV and an outer diameter of not more than 20 mm. The cable is placed in a flame with a temperature of not less than 830 °C simultaneously with a mechanical impact, and it is checked whether it continues to transmit signal or power. For larger-diameter cables, other parts of the GOST IEC 60331 series are applied.

Other indices designate additional properties: LS — reduced smoke and gas emission, HF — absence of halogens, LTx — low toxicity of combustion products. They are analysed in a separate material: table of differences between LS, HF, LSLTx, FRLS and FRHF.

Which Fire Properties Are Tested

GOST 31565-2012 establishes five fire hazard indicators. Each is confirmed by a separate test method.

Source: Table 1 of GOST 31565-2012; test methods — GOST IEC 60332-3-21, 60332-3-22, 60332-3-23; GOST IEC 60331-2-2021. A cable is assigned a fire hazard class based on the set of indicators.

The key difference is in the methods. In the ng test, the cable is in a bundle, ignited from below, and after a specified time the extent of flame spread is measured. In the FR test, the cable is in a flame, and it is checked whether it continues to transmit signal. These are two different tests, and one property does not follow from the other.

How the Versions Differ

Let us compare ng and FR by the characteristics that are important when selecting a cable for a specific line.

Source: compiled according to GOST 31565-2012, GOST IEC 60332-3-21, 60332-3-22, 60332-3-23, GOST IEC 60331-2-2021.

Fire resistance is provided by the cable design. One method is a two-layer insulation, where the first layer is a winding of mica-containing tapes, and the second is an extruded layer of PVC or a halogen-free polymer. The second method is insulation made of ceramising silicone rubber. When exposed to flame, the mica-containing tape or silicone rubber forms a ceramic barrier that preserves the dielectric properties and the integrity of the circuit.

The additional indices LS, HF, LTx work on top of the base property. A cable ng(A)-FRLS is fire-resistant and non-flame propagating, with reduced smoke emission. A cable ng(A)-FRHF is fire-resistant, non-flame propagating, halogen-free. These combinations are chosen when requirements are imposed on the line not only for fire resistance, but also for the composition of combustion products.

Where They Are Applied

The choice between ng and FR is determined by the purpose of the line. Below is the practical logic based on the predominant areas of application according to GOST 31565-2012 and the building norms of the Republic of Kazakhstan.

Industrial facilities. For cable structures, trestles, galleries, tunnels, versions with non-propagation of combustion in grouped installation are used: ng(A), ng(B). If the cable supplies a system that must operate during a fire, FR is added. For facilities with electronic equipment, where combustion products can damage the apparatus, HF is used.

Public buildings. For buildings with mass occupancy, multi-functional complexes, high-rise buildings, ng(A)-HF is used. The absence of halogens reduces the corrosion activity of combustion products. For lines that must maintain operability during a fire, FR is added.

Escape routes. For lighting of escape routes and warning systems, cables with reduced smoke emission and low toxicity are used: ng(A)-LSLTx. If these lines must operate during a fire, FR is added. The building norms of the Republic of Kazakhstan establish: the connecting and supply lines of fire automatics are made resistant to fire, must withstand a fire for 30 minutes or be protected so as to withstand the effects of fire for the same time.

Fire protection systems. For fire alarms, emergency lighting, smoke extraction, fire extinguishing systems, fire-resistant cables are used: ng(A)-FRLS or ng(A)-FRHF. The cable must maintain operability for the time required for evacuation and operation of fire extinguishing systems. In control and monitoring circuits of building fire protection systems, cables of the FRHF version are used, since the absence of halogens is important for the reliability of electronics.

Facilities with a large number of people and limited mobility. For hospitals, preschool institutions, nursing homes, schools, ng(A)-LSLTx is used. People in these institutions cannot quickly leave the building, therefore the requirements for the toxicity of combustion products are increased. For cable routes in buildings of preschool and educational institutions, according to GOST 31565-2012, cables with copper conductors, non-flame propagating (ng), fire-resistant (FR), with reduced smoke and gas emission (LS) and low toxicity (LTx) are used. An analysis of the fire-resistant version with areas of application is given in a separate material: Fire-resistant cable: complete selection guide.

For grouped installation, in any case, a version with the ng index is required. Single installation permits a cable without the ng index, but for most modern facilities, the grouped installation method predominates. The choice between VVG and VVGng is a separate practical task: VVG or VVGng: which cable to choose. The general classification of cables by fire safety and its connection with other norms are analysed in the material GOST 31565-2012: classification of cables by fire safety.

How to Choose the Cable Version

The selection algorithm is built from the conditions of the facility to the specific version.

1. Determine the installation method. Single or grouped. For grouped, the ng index with a category is required.
2. Determine whether the line must operate during a fire. If yes — FR is required. If not — ng is sufficient.
3. Determine the requirements for smoke emission. If the cable is laid in a room with people or on escape routes — LS is required.
4. Determine the requirements for halogens. If there is electronic equipment, server rooms, control rooms in the laying zone — HF is required.
5. Determine the requirements for toxicity. For facilities with limited mobility of people — LSLTx.
6. Assemble the version. The combination of indices gives a specific type: ng(A)-FRLS, ng(A)-FRHF, ng(A)-LSLTx.
7. Verify with regulatory requirements. GOST 31565-2012 establishes the classification, but specific requirements for the facility may be clarified in the design documentation and building norms. If the regulatory situation for the facility is ambiguous, the decision is made by the designer based on the current requirements.

Typical Mistakes

“ng means fire-resistant.” This is a misconception. ng — non-propagation of combustion in grouped installation. An ng(A) cable does not propagate combustion, but when exposed to flame it may char and stop working. Fire resistance is designated by the FR index and confirmed by a separate test for maintaining operability in a flame.

“If a cable does not propagate combustion, it will continue to work during a fire.” Non-propagation of combustion means that the flame will not travel along the bundle of cables. But the cable itself in the fire zone may lose operability. Maintaining operability is ensured only by the fire-resistant FR version.

“FR is needed for any cable line.” Fire-resistant cables are more expensive and stiffer to install due to mica-containing tapes or ceramising insulation. They are used where the cable must operate during a fire: fire protection systems, emergency lighting, smoke extraction. For ordinary power lines, a non-flame propagating version is sufficient.

“LS and HF are the same thing.” LS reduces smoke and gas emission but does not eliminate halogens. An ng(A)-LS cable contains PVC compound with chlorine. HF is the absence of halogens in the insulation and sheath materials. An ng(A)-HF cable does not emit halogen-containing gases, but its smoke formation may not be as low as that of specialised LS versions.

“The more indices, the better.” Each index reflects a specific property and increases the cost of the cable. If the facility does not require low toxicity, overpaying for LSLTx gives no practical benefit. The version is chosen according to the conditions of the facility, not on the principle of “maximum configuration”.

FAQ

Can ng(A)-FRLS be replaced with ng(A)-LS?

No. ng(A)-LS is not fire-resistant. If the cable supplies a fire protection system and must operate during a fire, replacement with a non-fire-resistant version is not allowed. For such lines, an FR version is required.

How is the fire resistance of a cable tested?

According to GOST IEC 60331-2-2021 for cables for rated voltages up to 0.6/1.0 kV and an outer diameter of not more than 20 mm. The cable is placed in a flame with a temperature of not less than 830 °C simultaneously with a mechanical impact, and it is checked whether it continues to transmit signal or power for a specified time. For larger-diameter cables, other parts of the GOST IEC 60331 series are applied.

Is the ng index sufficient for a cable line in a kindergarten?

No. For buildings of preschool and educational institutions, according to GOST 31565-2012, cables with copper conductors, non-flame propagating (ng), fire-resistant (FR), with reduced smoke and gas emission (LS) and low toxicity (LTx) are used. Specific requirements for the facility are established by the design documentation and building norms. If the regulatory situation is ambiguous, the decision is made by the designer.

How long does a fire-resistant cable maintain operability?

From 30 to 180 minutes, depending on the fire resistance category. The specific time is determined by the project. The building norms of the Republic of Kazakhstan establish a minimum requirement for fire automatics lines — 30 minutes. For critical systems, the designer may adopt a higher value.

What does a fire hazard class mean, for example P1a.7.2.2.2?

The fire hazard class is a sequence of indicators: flame propagation limit for grouped installation (P1a, P1b, P2, P3, P4), fire resistance limit (1–8), corrosion activity indicator (1 or 2), toxicity indicator (1 or 2). For example, P1a.7.2.2.2 is decoded as P1a, fire resistance limit 7, corrosion activity category 2, toxicity category 2.

Normative Sources Used

• GOST 31565-2012 “Cable products. Fire safety requirements” — in force, introduced 01.01.2014, amendment put into effect on 29.09.2025 — official text on meganorm.ru — confirms the classification of cables by fire hazard indicators and the types of versions ng, FR, LS, HF, LTx.
• GOST IEC 60331-2-2021 “Tests for electric cables under fire conditions. Circuit integrity. Part 2. Test method for cables of rated voltage up to and including 0.6/1.0 kV and with an overall diameter not exceeding 20 mm under flame with a temperature of at least 830 °C simultaneously with mechanical shock” — in force, introduced 01.01.2022 — official portal of Rosstandart, protect.gost.ru — confirms the fire resistance test method.
• GOST IEC 60332-3-21, 60332-3-22, 60332-3-23 — test methods for flame propagation along vertically arranged bundles of cables — in force — official texts of the standards — confirm the test methods for non-propagation of combustion in grouped installation.
• Building norms of the Republic of Kazakhstan (order of approval) — requirement for fire automatics lines to withstand a fire for 30 minutes or to be protected — in force — IPS “Adilet”, adilet.zan.kz — confirms the regulatory requirement for the fire resistance of fire automatics lines.
• GOST 31996-2012 “Power cables with plastic insulation for rated voltages of 0.66; 1 and 3 kV” — in force — official text of the standard — confirms the requirements for cable design.
• TR CU 004/2011 “On the safety of low-voltage equipment” — in force — official portal of the EAEU — confirms the mandatory certification of cables for voltages from 50 to 1000 V.
• Electrical Installation Code of the Republic of Kazakhstan 2015, as amended by the order of the Minister of Energy of the Republic of Kazakhstan dated 31.10.2022 No. 340 — in force — IPS “Adilet” — confirms the requirements for cable installation and protection.