NG(A), LS, HF, LSLTx, FRLS and FRHF: complete table of cable differences

Short Answer: How the Versions Differ

Each letter designation in the cable marking corresponds to a separate fire property. ng — non-propagation of combustion in grouped installation. LS — reduced smoke and gas emission. HF — absence of halogens in combustion products. FR — fire resistance, that is, maintaining operability in a flame. LTx — low toxicity of combustion products. These properties do not replace each other: a cable may not propagate combustion but not be fire-resistant, or be fire-resistant but emit halogens.

Combinations of indices give specific versions. ng(A)-LS — does not propagate combustion in grouped installation and emits less smoke. ng(A)-FRLS — fire-resistant, does not propagate combustion, with reduced smoke emission. ng(A)-FRHF — fire-resistant, does not propagate combustion and does not emit corrosion-active halogen-containing gases. 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.

What the Marking Means

The letter indices did not appear for marketing, but as a result of classification according to specific fire hazard indicators. Let us examine each index.

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.

LS (Low Smoke) — reduced smoke and gas emission. During combustion, the cable emits less smoke and gaseous products than an ordinary PVC cable. This is important for escape routes and rooms where smoke hinders people’s exit.

HF (Halogen Free) — absence of halogens. The insulation and sheath materials do not contain chlorine, fluorine or bromine. During combustion, such cables do not emit corrosion-active halogen-containing gases, which damage electronic equipment and are dangerous to breathe.

FR (Fire Resistance) — fire resistance. The cable maintains operability when exposed to flame for a specified time: from 30 to 180 minutes. This property distinguishes a fire-resistant cable from one that merely does not propagate combustion. A non-flame propagating cable may char and stop working; a fire-resistant one continues to transmit signal or power.

LTx (Low Toxic) — low toxicity of combustion products. During combustion, the cable emits fewer toxic substances. This is critical for enclosed spaces and facilities with mass occupancy, where combustion products are more dangerous than the fire itself.

An analysis of the specific LSLTx version with practical examples is given in a separate material: LSLTx Cable: GOST, decoding, characteristics, application.

Which Fire Properties Are Tested

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

Source: Table 1 of GOST 31565-2012. The values of the evaluation criteria and test methods are given in the standard. A cable is assigned a fire hazard class based on the set of indicators, for example P16.8.2.2.2 for the ng(A) version or P1a.8.2.2.2 for ng(A)-LS.

It is important to understand the difference between the tests. Non-propagation of combustion is checked on a bundle of cables: how far the flame has spread is assessed. Fire resistance is checked differently: the cable is in a flame, and it is checked whether it continues to transmit signal or power. These are two different tests, and one property does not follow from the other.

How the Versions Differ

Let us compare the versions by five characteristics: flame propagation, smoke formation, halogen content, corrosion activity of combustion products, toxicity, and maintenance of operability during a fire.

Source: compiled according to Section 6 of GOST 31565-2012. The category in brackets (A, B, C, D) indicates the stringency of the requirements for non-propagation of combustion in grouped installation. Category A is the most stringent.

The table shows that LS and HF are not the same thing. LS reduces smoke formation but does not eliminate halogens: PVC compound of reduced fire hazard still contains chlorine. HF eliminates halogens but does not necessarily reduce the toxicity of other combustion products. Fire resistance (FR) is a separate property that does not appear automatically when LS or HF is added.

Where They Are Applied

The choice of version is determined by the conditions of the facility. Below is the practical logic based on the predominant areas of application according to GOST 31565-2012.

Industrial facilities. For cable structures, trestles, galleries, tunnels, versions with non-propagation of combustion in grouped installation are used: ng(A), ng(B). If personnel work in the room and there is a risk of smoke, LS 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, which is important for the preservation of equipment and the safety of people.

Escape routes. For lighting of escape routes and warning systems, cables with reduced smoke emission and low toxicity are used: ng(A)-LSLTx. Smoke and toxic combustion products on escape routes are more dangerous than the flame itself, therefore LS and LTx are critical here.

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. An analysis of this version with areas of application — LSLTx Cable: GOST, decoding, characteristics, application.

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 differences between VVGng and VVGng-LS are analysed in the material VVGng or VVGng-LS: what is the difference and when LS is needed.

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 the requirements for smoke emission. If the cable is laid in a room with people or on escape routes — LS is required.
3. Determine the requirements for halogens. If there is electronic equipment, server rooms, control rooms in the laying zone — HF is required.
4. Determine the requirements for fire resistance. If the cable supplies fire protection systems — FR 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 fire safety norms. If the regulatory situation for the facility is ambiguous, the decision is made by the designer based on the current requirements.

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.

Typical Mistakes

“ng means fire-resistant.” Non-propagation of combustion and fire resistance are different properties. An ng(A) cable does not propagate combustion in grouped installation, 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.

“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.

“FR is needed for any cable line.” Fire-resistant cables are more expensive and stiffer to install. 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.

“If a cable does not propagate combustion, it will continue to work during a fire.” This is a misconception. 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.

“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

What does the digit or letter after ng mean?

The category indicates the stringency of the requirements for non-propagation of combustion in grouped installation. Categories: A F/R, A, B, C, D. Category A F/R 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.

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 does ng(A)-HF differ from ng(A)-LS?

ng(A)-HF does not contain halogens and does not emit corrosion-active gases during combustion. ng(A)-LS contains PVC compound of reduced fire hazard, which reduces smoke formation but emits hydrogen chloride during combustion. For rooms with electronics and server rooms, HF is preferable.

Is LSLTx mandatory for hospitals and schools?

GOST 31565-2012 refers LSLTx to the predominant area of application for preschool and educational institutions, specialised nursing homes for the elderly and disabled, hospitals, and dormitory buildings of boarding-type educational institutions. Specific requirements for the facility are established by the design documentation and fire safety norms. If the regulatory situation is ambiguous, the decision is made by the designer.

What does a fire hazard class mean, for example P16.8.2.2.2?

The fire hazard class is a sequence of indicators: flame propagation limit for single installation (O1 or O2), 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, P16.8.2.2.2 is decoded as P1b, fire resistance limit 8 (30 minutes), 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
• Amendment to GOST 31565-2012 (put into effect on 29.09.2025) — in force — official publication of Rosstandart, protect.gost.ru
• 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
• GOST IEC 60331-21, 60331-23 — fire resistance test methods — in force — official texts of the standards
• 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
• TR CU 004/2011 “On the safety of low-voltage equipment” — in force — official portal of the EAEU
• 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”