Cable Knowledge
What Is LSZH Cable and When Is It Needed?
LSZH stands for low smoke, zero halogen. It describes how a cable material behaves when it burns under specified fire tests: how much smoke it gives off and how much halogen acid gas it releases. It does not on its own show that a cable is flame-retardant, fire-resistant or suitable for every outdoor installation.
What does LSZH mean and what does it measure?
LSZH is short for low smoke, zero halogen. The name points to two properties of the cable material when it burns: the amount of smoke it produces and whether it releases halogen acid gas. Both are measured in standard tests rather than judged by eye.
"Zero" is a common label rather than a literal limit. In practice a specification sets a test value. A common LSZH acceptance value for halogen acid gas is 0.5 % (5 mg/g) under IEC 60754-1.
Why do projects specify LSZH cable?
Dense smoke can make evacuation harder, and corrosive gases can damage electrical and electronic equipment after a fire. For that reason, tunnels, transport systems, public buildings, data centres and other enclosed facilities often specify low smoke and halogen-free cables.
The reason is the hazard to people and equipment inside the building. It is not a guarantee that a circuit keeps running during a fire. That is a different property and needs its own test.
Which fire tests apply to LSZH cable?
Each test covers one property, and results from different tests are not interchangeable. A pass in one test does not show a pass in another. The table lists the tests most often named in LSZH and fire-performance specifications.
| Test standard | What it measures | Common acceptance value | What it does not tell you |
|---|---|---|---|
| IEC 60754-1 | Halogen acid gas released from burning cable material | At most 0.5 % (5 mg/g), a common LSZH value | Smoke density, flame spread or circuit integrity |
| IEC 60754-2 | pH and conductivity of water that absorbs the gases from the test | pH at least 4.3 and conductivity at most 10 µS/mm, given as recommended values in Annex A | How much smoke is produced, or whether the cable keeps working in fire |
| IEC 61034-2 | Light transmittance through the smoke in a test chamber | At least 60 % light transmittance is commonly used to classify low smoke; some sectors require more | Toxicity of the smoke, or how smoke behaves in a real building |
| IEC 60332-1-2 | Flame spread on a single vertical cable | Pass under the test conditions of the edition named in the specification | How bunched cables behave, or whether a circuit keeps working |
| IEC 60332-3 | Flame spread on bunched cables, graded by the volume of non-metallic material per metre | Category A to D, chosen by the project requirement | Performance of a single cable, or of a bundle with a different volume |
| IEC 60331 | Circuit integrity: whether a circuit keeps working in fire | Current parts 60331-1 and -2 use at least 830 °C with mechanical shock; duration is set by the product standard or project | Smoke, halogen content or flame spread |
| BS 6387 | Circuit integrity in categories C, W and Z | Category C: 950 °C for 3 h with fire alone; CWZ adds water and mechanical shock | Smoke or halogen content |
These are commonly cited acceptance levels. The edition of each standard and the project's own requirement decide the actual limit, so copy the exact wording into the specification.
Is LSZH the same as flame-retardant or fire-resistant?
No. The three terms describe different properties, and they should not be used as synonyms in a specification.
- LSZH describes smoke density and halogen acid gas under specified tests.
- Flame-retardant performance is judged by flame-spread tests, such as IEC 60332-1-2 for a single cable and IEC 60332-3 for bunched cables.
- Fire-resistant performance is judged by circuit-integrity tests, such as IEC 60331 or BS 6387, which check whether a circuit keeps working during fire.
A cable can be LSZH and still fail a flame-spread test, and a fire-resistant cable is not automatically low-smoke or halogen-free. For more detail on these terms, see flame-retardant and fire-resistant cable.
What does an LSZH claim not prove?
An LSZH material claim on its own does not establish the flame category, circuit integrity, outdoor life or mechanical durability of a cable. Each of those needs its own evidence.
- Do not treat halogen-free as a substitute for fire-resistant.
- Ask for the complete cable test reports, not only a statement about the compound.
- Confirm that the sheath suits the real environment, including moisture and temperature.
What are the trade-offs of LSZH compounds?
LSZH compounds can differ from PVC in flexibility, abrasion resistance, water absorption and processing. These differences can matter as much as the fire result when the cable is pulled through ducts, buried or exposed to wet conditions.
Insulation is chosen separately from the sheath. For insulation options, see the XLPE insulated power cable page, and ask the supplier to state both the insulation and sheath materials on the datasheet. If the cable must also be armoured, ask whether BS 6724, which covers LSZH-sheathed armoured cable, applies.
What to confirm before ordering
- The project fire strategy and which fire tests it names.
- The exact smoke, halogen and flame-spread standards, with edition and acceptance criteria.
- Whether circuit integrity is required, and to which test (for example IEC 60331 or BS 6387).
- Cable voltage rating, conductor and construction.
- Indoor, outdoor, underground or wet service conditions.
- Mechanical duty: bending, pulling, abrasion, and whether armour is needed.
- Required approvals, type-test reports and marking.
- Minimum bending radius and temperature limits, taken from the manufacturer's datasheet.
Frequently asked questions
Is LSZH cable the same as fire-resistant cable?
No. LSZH describes smoke and halogen acid gas under specified tests, while fire-resistant cable is judged by circuit-integrity tests such as IEC 60331 or BS 6387.
Does LSZH mean the cable will not burn?
No. The LSZH tests look at smoke and halogen gas, and flame spread is covered by separate tests.
What is a common LSZH limit for halogen acid gas?
A common LSZH acceptance value is 0.5 % (5 mg/g) under IEC 60754-1. Confirm which edition the supplier's test report uses.
Is a halogen-free claim enough for a specification?
No. Name the test standards, acceptance values, cable voltage and installation conditions, and ask for the reports that prove them.
Does LSZH suit outdoor or wet installations?
Not automatically. LSZH compounds can differ from PVC in water absorption and abrasion resistance, so check the sheath against the real environment.
What should I ask a supplier for first?
Ask for the datasheet and the full type-test reports, with the standard editions named, before comparing prices.
References
- Caledonian Cables FAQ on LSZH testingBackground on the halogen acid gas and smoke tests behind LSZH claims.
- Prysmian: how fire-resistant cables are testedOverview of circuit-integrity testing for fire-resistant cable.
- Voltimum on cable fire performance standardsSummary of the fire performance standards named in this article.
- Mass Transit on misconceptions about fire-performance termsSupports the point that LSZH, flame-retardant and fire-resistant are often confused.
Related cable products
- XLPE Insulated Power Cable
- PVC Insulated Power Cable
- Control Cable
- Rubber Flexible Cable
- Welding Cable
- Solar PV Cable
Continue reading
- What Standards and Test Reports Can Cable Buyers Request?
- How Do Copper Price and Quantity Affect Cable Price?
- How to Choose Solar PV Cable for a Photovoltaic Project
- How to Choose Rubber Flexible Cable or Welding Cable
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