What is Halogen-Free (HF) cable? When to use N2XH and N2XY cables

Halogen-free cable is a cable where the insulation and sheath are made from a polymer compound without halogens, rather than PVC; in designations such as N2XH and N2XHY, this is indicated by the HF (halogen-free) suffix. According to the requirements for halogen-free performance, two key criteria are met: the release of halogen acid gases (expressed as HCl) is limited to a maximum of 5.0 mg/g, and the reduction in light transmission during smoke evolution is limited to no more than 40% — compared to the 50% limit allowed for LS (low smoke) versions.

Because such a sheath does not release hydrogen chloride when burning, no acids are formed that could settle on circuit boards in humid air or irritate the respiratory tract.

These cable types are used where the composition and smoke density are critical during a fire: in buildings and structures with high occupancy, including multi-purpose high-rise buildings and large complexes. These are precisely the areas where halogen-free performance is preferred.

The two main types are distinguished by their insulation. For N2XH, the insulation is a halogen-free compound with a maximum conductor temperature of 70 °C. For N2XHY, the insulation is cross-linked polyethylene (XLPE) with a maximum temperature of 90 °C, which allows for a higher current-carrying capacity for the same cross-section. For fire protection systems, versions with an FR (fire-resistant) rating are used, such as N2XH with fire resistance according to EN 50200.

What the HF designation entails

The HF index regulates two distinct requirements:

• Halogen content: the amount of halogen acid gases expressed as HCl is no more than 5.0 mg/g; the conductivity of the aqueous solution is no more than 10.0 μS/mm; and the pH is no less than 4.3. Testing is performed in accordance with IEC 60754-1 and IEC 60754-2;
• Smoke density: the reduction in light transmission must not exceed 40%. For LS (low smoke) versions, the threshold is more lenient at 50%.

When PVC burns, it releases hydrogen chloride, which turns into acid in the presence of moisture; this acid corrodes equipment and damages the respiratory tract. A halogen-free compound prevents this. However, "halogen-free" and "non-flammable" are different concepts: flame retardancy (the prevention of flame spread) is a separate characteristic, while maintaining circuit integrity during a fire is defined by the fire resistance (FR) rating.

The toxicity of combustion products is standardised as a separate parameter. For LS and HF versions, the equivalent toxicity index is greater than 40 g/m³ (clause 5.6), while for LTx-rated versions, it is greater than 120 g/m³ (clause 5.9); the higher the value, the lower the toxicity of the combustion products. LTx refers specifically to toxicity, not smoke density.

Where halogen-free versions are truly required

According to standard guidelines, halogen-free (HF) versions are intended for internal electrical installations in buildings and structures with high occupancy, including multi-purpose high-rise buildings and large complexes. These areas are considered preferred locations for such cables. This serves as a technical guideline rather than a universal prohibition.

The necessity of using specific cables in a particular project arises from a different regulatory chain:

• Building regulations require that cables installed in open areas must be non-flammable;
• Lines for fire protection systems must maintain operational integrity during a fire for the duration required to perform their functions (the basis for using FRHF/fire-resistant cables);
• Technical codes, industry-specific requirements, and for specific sites, the approved design documentation or maritime classification society requirements.

Therefore, specifications should refer to the design solution and applicable technical codes. Simply stating "HF is mandatory per standard" is insufficient to resolve disputes during technical audits or inspections.

Markings for halogen-free power cables

Note for this entire section: markings follow harmonised classification systems, but actual manufacturing follows the manufacturer's technical specifications—always verify characteristics against the specific manufacturer's datasheet.

N2XH — a standard halogen-free cable. The designation indicates a halogen-free polymer insulation compound, a halogen-free sheath, and no protective armouring.

N2XH-FRHF — similar to standard halogen-free cables, but designed to maintain circuit integrity during a fire, suitable for emergency lighting, fire pumps, and smoke extraction ventilation. The letters "FR" do not specify the exact duration the cable must remain operational in a fire; this value is defined by the manufacturer's technical specifications. Standard testing scales typically range from 30 to 180 minutes, and for an FR-rated cable, the lower threshold of 30 minutes is often sufficient. A rating of "180 minutes" represents the top of this scale and must be verified by technical documentation rather than the product designation itself. Where specific requirements are not defined, IEC 60331 recommends testing for a duration of 90 minutes.

N2XH-HF (flat) — a flat-profile version designed for concealed installation; the flat shape is indicated by the specific geometry of the product.

N2XH-HF-PUR (cold-resistant) — a version designed for low-temperature environments. While standard cables are typically rated for a range from −50 °C to +50 °C (or −60 °C to +50 °C for those with polyethylene outer sheaths), cold-resistant versions extend the lower temperature limit, with the exact value specified by the manufacturer's technical data.

N2XH-HF (screened) and N2XH-FRHF (screened) — screened versions (containing a metallic screen) intended for automation circuits and low-voltage systems running alongside power lines.

Cables with XLPE insulation

N2XY-HF and N2XY-FRHF — feature cross-linked polyethylene (XLPE) insulation combined with a halogen-free sheath. XLPE can withstand higher conductor temperatures: 90 °C for continuous operation and 130 °C during overload, compared to 70 °C and 90 °C for PVC or standard halogen-free compositions. In practical application, this allows for a higher current-carrying capacity for the same cross-section.

The scope of these standards covers cables rated for 0.66, 1, and 3 kV. Any equipment operating at higher voltages is manufactured according to different standards, and its characteristics must be verified separately.

NYM-J or N2XH-HF

The choice between NYM-J and N2XH-HF comes down to five key criteria: material, halogen content, smoke emission, toxicity, and the primary application area.

Parameter	NYM-J (LS)	N2XH (HF)
Insulation and sheath material	PVC	Halogen-free polymer compound
Halogen acid gas emission during combustion	Not regulated	Not more than 5.0 mg/g expressed as HCl (Clause 5.7)
Smoke density	Light transmission reduction not more than 50% (Clause 5.4)	Not more than 40% (Clause 5.5)
Toxicity of combustion products	More than 40 g/m³ (Clause 5.6)	More than 40 g/m³ (Clause 5.6); stricter requirements apply only to LTx versions (Clause 5.9)
Primary application (Table 2)	Indoor electrical installations, buildings, enclosed cable structures	Buildings with high occupancy, high-rise buildings, and complexes

Please refer to the catalogue for price differences: costs depend on the manufacturer, cross-section, and batch size, so there is no fixed percentage provided in this article.

Where HF compounds fall short compared to PVC

A halogen-free (HF) compound is a compromise rather than an improvement in every category. Such sheaths are generally less resistant to UV radiation and prolonged moisture exposure, behave more rigidly during installation in freezing temperatures, and the cable is more expensive than its PVC counterpart. Specifying HF "just in case" outside of areas where it is strictly required results in unnecessary costs in the budget. Always check the specific technical data sheet for the operational limitations of a particular brand.

Common specification errors

• HF is mistaken for fire resistance. HF refers to halogen content and smoke density. Circuit integrity during a fire is provided only by the FR (fire-resistant) rating (Clause 5.8).
• FRHF is expected to provide 180 minutes of integrity. The duration is specified in the manufacturer's technical data; FR must meet at least Class 7 of Table 1, which is a minimum of 30 minutes.
• LTx is confused with smoke density. LTx regulates toxicity (Clause 5.9), whereas smoke density is regulated by LS and HF ratings.
• HF is specified for underground sections "for reliability". Standard requirements for building cables do not apply to cables intended for direct burial in earth or water (Section 1); in those cases, mechanical protection and sheath durability are the deciding factors.
• Different versions are mixed in a single cable bundle. Flame spread is regulated for the entire bundle (Clause 5.10), meaning a single cable with an inferior rating invalidates the performance of the others.

Standards and regulations

The requirements discussed in this article follow from these standards used in the European Union:

• EN 50575 — Power, control and communication cables — cables for general applications in construction works subject to reaction to fire requirements
• EN 13501-6 — Fire classification of construction products — Part 6: classification using data from reaction to fire tests on cables
• EN 60754-1 — Test on gases evolved during combustion of materials from cables — Part 1: determination of halogen acid gas content
• EN 60754-2 — Test on gases evolved during combustion of materials from cables — Part 2: determination of acidity (pH) and conductivity
• HD 603 S1 (IEC 60502-1) — Distribution cables of rated voltage 0.6/1 kV
• IEC 60331-21 — Tests for electric cables under fire conditions — circuit integrity — Part 21: cables of rated voltage up to and including 0.6/1.0 kV
• EN 61034-2 — Measurement of smoke density of cables burning under defined conditions — Part 2: test procedure and requirements