A low smoke halogen-free cable (LSZH / LS0H / LSOH / LSHF / HFFR) is a power, control or data cable whose insulation, bedding and sheath contain no added fluorine, chlorine or bromine and which, when burned under the specified tests, releases little visible smoke and little corrosive acid gas. The three tests that close the definition are IEC 60754-1/-2 (halogen acid and acidity), IEC 61034-2 (3 m cube smoke, typically ≥60 % light transmittance) and a flame-spread clause — IEC 60332-1-2 on a single cable and usually IEC 60332-3 Category A/B/C on a bunch. The jacket compound on 0.6/1 kV power cable is IEC 60502-1 type ST8, conductor temperature 90 °C. LSZH is a material system. It is not a CPR Euroclass and not a fire-resistance rating (IEC 60331 / BS 6387).

Constructions we supply / tool for

Conductor: IEC 60228 Class 2 or Class 5, plain or tinned. Insulation: XLPE or halogen-free EI5 / cross-linked polyolefin — not PVC. Colour: often black or grey RAL 7001; print must list the test numbers, not only “LSZH”. Send section, armour yes/no, CPR class if EU building, rail HL if rolling stock.

What Is Low Smoke Halogen-Free Cable?

A low smoke halogen-free cable is a cable whose polymeric layers are formulated without halogenated flame retardants so that a fire produces little opaque smoke and little hydrogen halide, while still meeting a stated flame-spread test.

PVC jackets contain chlorine. In fire they evolve dense smoke and HCl that attacks eyes, lungs and switchgear. LSZH compounds replace that chemistry with a polyolefin or EVA/PE matrix loaded with aluminium trihydrate (ATH) أو magnesium hydroxide (MDH) at typically 50–65 % by weight. The hydrate decomposes endothermically, releases water vapour, dilutes fuel gas and leaves an oxide char. That is why smoke stays low and why there is no halogen acid to measure — provided the whole cable, including tapes and fillers, is halogen-free. A PVC-bedded “LSZH sheath” fails IEC 60754 on the complete sample. ICEA T-33-655-2023 states the same caution for jackets alone.

Labels LSZH, LS0H, LSOH, LSHF, HFFR, FRNC, LSF are commercial synonyms. None of them is a fire class. The datasheet must name IEC 60754, IEC 61034, IEC 60332-x and, for EU buildings, the CPR declaration (B2ca / Cca / Dca + s1, d1, a1). FRLS (flame-retardant low-smoke PVC) still contains halogen and is not LSZH.

How do LSZH, PVC, FRLS and XLPE-PVC jackets differ in a fire?

PVC and FRLS release halogen acid. LSZH does not. XLPE insulation is already halogen-free; the jacket decides the smoke and acid numbers unless the bedding is PVC.

IEC 60502-1:2021 Table 4 lists ST8 as the halogen-free thermoplastic sheath at 90 °C. The 2021 edition added ST8 mechanical language that older 2004 sheets do not carry. BS 6724 is the UK armoured LSZH counterpart to PVC BS 5467. EN 50525-3-11 / 3-21 / 3-31 cover 450/750 V halogen-free building wires still listed under the LVD harmonised set in 2025.

Flame-resistant (circuit integrity, IEC 60331 or BS 6387) is a mica-tape or MI construction. An LSZH jacket does not keep the circuit alive. Specify both if the emergency circuit requires it: e.g. Cu/Mica/XLPE/LSZH.

Where must LSZH be specified — and where is PVC still acceptable?

Specify LSZH wherever people must evacuate through the same volume as the burning cable: tunnels, metros, hospitals, data halls, high-rise risers, ships and rolling stock. PVC remains acceptable on outdoor overhead and many industrial trays where smoke is not the design constraint.

Mandatory or de-facto LSZH

• Public buildings and escape routes (EU CPR + national codes).
• Metro / rail tunnels and rolling stock — EN 45545-2 HL2 or HL3, R15 interior / R16 exterior.
• Ships and offshore — IEC 60092-353:2024 plus SHF1 (thermoplastic) or SHF2 (cross-linked, oil/mud).
• Data centres and telecom rooms — IEC 61034 visibility + 60332-3 bunch.
• 0.6/1 kV indoor power to IEC 60502-1 when the purchaser writes ST8.

Still PVC in many specs

• Outdoor distribution, aerial bundled, industrial plant with high mechanical abuse and no enclosed escape path.
• Domestic twin-and-earth in markets that only require Eca.

Rail HL3 (long tunnels, sleepers) tightens smoke (ISO 5659-2 Ds 4 min often ≤150) and toxicity (CIT). That compound is usually MDH-based and may be cross-linked; a standard ATH ST8 building-wire jacket will not pass HL3. Do not put “LSZH” on a rail RFQ without the HL and R-set.

Which tests and compound rules belong on the purchase order?

Write the test methods and the numeric limits. Do not write only “LSZH to IEC”.

Halogen and acidity

• IEC 60754-1: halogen acid gas, commonly <0.5 % by mass on the cable materials used.
• IEC 60754-2: pH ≥4.3 and conductivity limit (non-corrosive).
• ICEA T-33-655-2023: halogen-free jacket <0.2 % any halogen — jacket only; other layers can still spoil the cable result.

Smoke

• IEC 61034-1/-2 (3 m cube): project limit usually ≥60 % light transmittance.
• CPR additional smoke: EN 50399 → s1 / s2 / s3.

Flame

• IEC 60332-1-2:2025 (single vertical, 1 kW).
• IEC 60332-3-22/-23/-24/-25: bunched Categories A, B, C (Cat. A is the severe tray case).
• CPR: EN 50399 + EN 60332-1-2 → B2ca / Cca / Dca + s, d, a.

Sheath mechanics (power)

• IEC 60502-1 ST8 + IEC 60811 tensile/elongation/ageing.
• Thickness still follows ts = 0.035 D + 1.0 mm with the same minima as other 60502-1 oversheaths.

Compound process window
ATH dehydrates at about 180–220 °C. Extrude below that or the jacket foams. MDH dehydrates at about 300–330 °C and is used when the melt must run hotter (XL, rail, 125 °C class). Loading 50–65 % raises specific gravity to ~1.45–1.55 and cuts elongation versus PVC; that is why LSZH jackets mark and tear more easily on steel trays.

What fails when “LSZH” is treated as a complete specification?

PVC bedding under an LSZH sheath, missing bunch-burn, CPR class assumed from the letters, and ATH foam from a hot PVC screw are the four defects that fail type test or installation.

1. Cu/XLPE/PVC/SWA/LSZH — the PVC bedding fails 60754 on the complete cable. Write LSZH/SWA/LSZH.
2. Pass 60332-1, fail 60332-3 Cat. A — single-cable flame is not a tray test. State the category.
3. “LSZH = Cca-s1,d1,a1” — false. CPR is a separate declaration on the finished cable.
4. Porous ST8 — PVC zone card on ATH compound. Use an LSZH screw, melt <200 °C.
5. Jacket splits on SWA — high filler, tight armour, cold bend. Check 60811 cold impact and armour bedding thickness.
6. Rail HL3 demanded on a 70 °C building-wire compound — wrong polymer and wrong smoke test (ISO 5659 vs IEC 61034).
7. Fire-resistant circuit specified as LSZH only — add mica or MI; ST8 does not give 180 min integrity.

2024–2026: IEC 60092-353 Edition 5 (2024) keeps separate halogen-free and low-smoke tables for ship cable; IEC 60332-1-2 Edition 2 (2025) is the current single-vertical text; IEC 60502-1:2021 ST8 is the LV power jacket to put on new sheets; CPR remains the EU building filter that LSZH letters do not replace; ATH/MDH polyolefin is still the volume chemistry, with bio-based FR in the literature but not yet the default ST8.

Key takeaways

• LSZH means no added halogen + low smoke + a stated flame test. The letters alone are not a class.
• Close the spec with IEC 60754-1/-2, IEC 61034-2 (≥60 %), IEC 60332-1 and/or -3, ، و ST8 on 0.6/1 kV jackets.
• Armoured build is LSZH / SWA or AWA / LSZH, not PVC bedding.
• ATH compounds extrude <200 °C; MDH is for hotter / rail / XL melts.
• CPR Euroclass and IEC 60331 fire resistance are separate orders.

Send mm², cores, armour, CPR or EN 45545 HL, and 60332-3 category.

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