LSZH Building Wire Family
Low-smoke, zero-halogen power and control wiring.
H07Z-K is the harmonised designation for LSZH (Low Smoke Zero Halogen) single-core flexible wire. National Cables manufactures this range on our IS 17048:2018 production track, delivering a 1100V dielectric margin verified by 3kV AC routine testing. Formal BIS certification applies to sizes up to 10 mm²; larger industrial cross-sections (up to 240 mm²) are manufactured to identical NABL-verified fire safety standards.
Decoding the LSZH Harmonised Designations
The harmonised code system identifies the voltage class and conductor flexibility for each family member:
| Designation | Voltage | Conductor class | Primary application |
|---|---|---|---|
| H05Z-K | 300/500V | Class 5 (flexible) | Internal panel wiring (0.5 – 1.0 mm²) |
| H07Z-U | 450/750V | Class 1 (solid) | Fixed lighting circuits and short conduit runs |
| H07Z-R | 450/750V | Class 2 (stranded) | Infrastructure power feeders in trays/conduits |
| H07Z-K | 450/750V | Class 5 (flexible) | Switchgear, PDUs, and tight-routing enclosures |
| (N)HM-J | 300/500V | Class 1 / 2 (Rigid) | Sheathed LSZH: Halogen-free surface-mount feeders for hospitals and metros. |
Metro and Data Center "Project Staples"
The following sizes represent the most common institutional specifications for LSZH infrastructure.
H07Z-R 2.5 mm² (Stranded)
Feeder standard: Used for primary Metro station lighting and power circuits.
· R at 20°C: 7.41 Ω/km
· Current (Method C): 34A
H05Z-K 1.0 mm² (Flexible)
Panel standard: Standard for control gear and PDU internal wiring.
· R at 20°C: 19.5 Ω/km
· Voltage: 300/500V (harmonised)
Construction and electrical characteristics.
| Parameter | Value / Description |
|---|---|
| Standard | EN 50525-3-40 & EN 50525-3-41 (harmonised) / IS 17048:2018 (ISI up to 10 mm²) |
| Voltage class | 300/500V (H05 designation) · 450/750V (H07 designation) · 1100V (IS 17048 track) |
| Conductor variants | H07Z-U (solid Class 1) · H07Z-R (stranded Class 2) · H05Z/H07Z-K (flexible Class 5) |
| Size range | 0.5 – 1.0 mm² (flexible) · 1.5 – 4.0 mm² (solid) · 1.5 – 240 mm² (stranded/flexible) |
| Conductor material | Plain annealed electrolytic copper — IEC 60228 / IS 8130:2013 |
| Conductor class | Per variant — Class 1 (H07Z-U) · Class 2 (H07Z-R) · Class 5 (H05Z-K / H07Z-K); flexible: max single wire Ø 0.26mm (1.5mm²) to 0.51mm (≥70mm²) |
| Insulation type | LSZH — halogen-free thermoplastic polyolefin compound (Type LSH1 per EN 50363-5) |
| Max conductor temperature | 90°C continuous · 200°C short circuit (5s) |
| Operating temperature range | −25°C to +90°C (static and flexed use) |
| Min. bending radius | 4 × OD (up to 35mm²) · 6 × OD (50mm² and above) |
| Flame retardancy | IEC 60332-1-2:2004 (single wire) · IEC 60332-3-24:2018 (bunched) |
| Halogen content | ≤0.5% HCl emission — IEC 60754-1 |
| Acidity / corrosivity | pH ≥4.3 · conductivity ≤10 µS/mm — IEC 60754-2 |
| Smoke density | Light transmittance ≥60% in 3m³ chamber — IEC 61034-2 |
| Insulation resistance at 90°C | Typically 0.003–0.015 MΩ·km depending on size — confirm on project datasheet |
| Colour availability | Red · Black · Blue · Orange · White · Yellow · Green/Yellow · Grey · Brown · Violet · Pink |
| Packing | 100m Coils (up to 6.0 mm²) or 500m/1000m ISPM-15 Fumigated Wooden Drums for all classes |
The LSZH Family: U, R, K, and Sheathed (N)HM-J
Class 1 conductor
Class 2 conductor
Class 5 conductor
Double-Layer LSZH System
Rigid Feeder vs. Flexible Panel Wiring
National Cables provides the specific conductor class required for your installation method.
H07Z-R (Stranded Class 2)
Primary Use: Fixed power feeders in cable trays and conduits. Preferred for long straight runs in metro tunnels and data centers due to its structural rigidity and lower voltage drop.
H07Z-K (Flexible Class 5)
Primary Use: Internal panel wiring and switchgear. Essential for tight routing in PDU cabinets, control marshalling boxes, and rolling stock harnesses.
(N)HM-J / (N)HM-O Sheathed LSZH Cable
National Cables' (N)HM-J features LSZH cores (Type LSH1) inside a protective LSZH outer sheath. This double-layer system is suitable for fixed installations in public buildings requiring high fire safety and low smoke emission.
1100V Dielectric Advantage
Manufactured on the 1100V IS 17048 track. Every (N)HM-J export build undergoes a 3kV AC routine test, providing superior dielectric strength for critical life-safety feeders in airports and tunnels.
Fire performance — halogen and smoke test requirements.
PVC releases hydrogen chloride when burning — corrosive to electronics and toxic during evacuation. The LSZH tests that define compliant performance are IEC 60754-1, IEC 60754-2, and IEC 61034-2. IS 17048:2018 mandates all three.
| Test | What it measures | Requirement | IS 17048:2018 / EN 50525-3-41 status |
|---|---|---|---|
| IEC 60754-1 | Halogen acid gas content — weight of HCl equivalent released per gram of compound burned at 935°C | ≤0.5% HCl by mass | Mandatory in both IS 17048:2018 and EN 50525-3-41 |
| IEC 60754-2 | Acidity and conductivity of absorption solution — measures corrosiveness of combustion gases to electronic equipment | pH ≥4.3 · conductivity ≤10 µS/mm | Mandatory in both standards |
| IEC 61034-2 | Smoke density in 3m³ chamber — measures light transmittance through smoke generated by burning 1m cable sample | Transmittance ≥60% (PVC typically <10%) | Mandatory in both standards |
| IEC 60332-1-2:2004 | Single wire flame propagation — measures whether fire travels up an individual cable when exposed to 1kW flame for 60 seconds | Char length ≤54mm above burner bottom edge | Mandatory in both standards |
| IEC 60332-3-24:2018 | Bunched cable flame propagation — measures fire spread when multiple cables are grouped in an installation tray or conduit | Category C — 0.5 litre/metre of cable | Mandatory in EN 50525-3-41; IS 17048:2018 specifies IEC 60332 category per project specification |
Dimensional Comparison: Rigid (R) vs. Flexible (K)
Stranded Class 2 (H07Z-R) and Flexible Class 5 (H07Z-K) differ in their overall diameter and packing density. Values cross-verified against international benchmarks. Project-specific inkjet marking includes sequential meter counts and NC internal batch traceability.
| Size (mm²) | Insul. wall (mm) | OD H07Z-R (mm) | OD H07Z-K (mm) | Weight H07Z-R (kg/km) | Weight H07Z-K (kg/km) | Max R Class 2 (Ω/km) |
|---|---|---|---|---|---|---|
| 1.5 | 0.7 | 3.0 | 2.9 | 21 | 20 | 12.1 |
| 2.5 | 0.8 | 3.7 | 3.6 | 33 | 31 | 7.41 |
| 4.0 | 0.8 | 4.2 | 4.1 | 49 | 47 | 4.61 |
| 6.0 | 0.8 | 4.8 | 4.7 | 69 | 66 | 3.08 |
| 10.0 | 1.0 | 6.0 | 5.9 | 112 | 108 | 1.83 |
| Industrial Feeder Range (H07Z-R / H07Z-K) | ||||||
| 35.0 | 1.2 | 9.8 | 9.6 | 355 | 342 | 0.524 |
| 70.0 | 1.4 | 13.2 | 13.0 | 695 | 675 | 0.268 |
| 240.0 | 2.2 | 24.2 | 24.0 | 2380 | 2320 | 0.0754 |
Rated current in amperes — four installation methods.
Per BS 7671:2018+A2:2022 Table 4E1A (90°C thermoplastic single core). Ambient temperature 30°C. Where terminations are rated to 70°C, apply the corresponding 70°C ratings instead.
| Size (mm²) | Method A Conduit in insulated wall | Method B Conduit on wall/trunking | Method C Clipped direct | Max R Ω/km | |||
|---|---|---|---|---|---|---|---|
| 2-cable 1φ A | 3/4-cable 3φ A | 2-cable 1φ A | 3/4-cable 3φ A | 2-cable 1φ A | 3/4-cable 3φ A | ||
| 1.5 | 19 | 17 | 23 | 20 | 25 | 23 | 13.3 |
| 2.5 | 26 | 23 | 31 | 28 | 34 | 31 | 7.98 |
| 4.0 | 35 | 31 | 42 | 37 | 46 | 41 | 4.95 |
| 6.0 | 45 | 40 | 54 | 48 | 59 | 54 | 3.3 |
| 10.0 | 61 | 54 | 75 | 66 | 81 | 74 | 1.91 |
| 16.0 | 81 | 73 | 100 | 88 | 109 | 99 | 1.21 |
| 25.0 | 106 | 95 | 133 | 117 | 143 | 130 | 0.780 |
| 35.0 | 131 | 117 | 164 | 144 | 176 | 161 | 0.554 |
| 50.0 | 158 | 141 | 198 | 175 | 228 | 209 | 0.386 |
| 70.0 | 200 | 179 | 253 | 222 | 293 | 268 | 0.272 |
| 95.0 | 241 | 216 | 306 | 269 | 355 | 326 | 0.206 |
| 120.0 | 278 | 249 | 354 | 312 | 413 | 379 | 0.161 |
Method A: enclosed in conduit in a thermally insulating wall. Method B: enclosed in conduit on a wall or in trunking. Method C: clipped direct to surface. Source: BS 7671:2018+A2:2022 Table 4E1A (BS EN 50525-3-41 / IEC 60228 Class 5).
Approximate Voltage Drop (mV/A/m) — 90°C Conductor
Design data for H07Z-R and H07Z-K in 3-phase AC circuits.
| Size (mm²) | 1.5 | 2.5 | 4.0 | 6.0 | 10.0 | 16.0 | 25.0 |
|---|---|---|---|---|---|---|---|
| Voltage drop | 29.0 | 18.0 | 11.0 | 7.3 | 4.4 | 2.8 | 1.8 |
H07Z-K outperforms H07V-K at elevated ambient temperatures.
At elevated ambient temperatures, H07Z-K's 90°C conductor rating requires less de-rating than H07V-K at 70°C. The same cross-section carries more current at 45°C ambient.
Example: 10mm² Method C panel wiring at 45°C ambient in Dubai or Lagos:
· H07V-K: 81A (H07V-K Method C at 30°C) × 0.79 = 64A usable
· H07Z-K: 81A (H07Z-K Method C at 30°C) × 0.87 = 70A usable — a 9% real-world current advantage with no change in cable size.
Specialized Underground & Metro Variants
For deep-tunnel and underground station wiring, we offer Anti-Termite and Anti-Rodent LSZH compounds as a project-specific variant. These formulations incorporate non-toxic repellent additives that prevent cable failure due to pest-driven sheath damage in critical railway and rail-metro environments.
Where H07Z-K is specified — and why.
H07Z-K is the default flexible single-core wire wherever fire safety regulations require halogen-free cable. This covers a broad range of infrastructure, commercial, and industrial applications globally.
| Application | Why H07Z-K is specified | Relevant standard / regulation |
|---|---|---|
| Metro & Rail rolling stock | Underground and enclosed environments — zero-halogen mandatory for evacuation safety; smoke cannot obstruct egress | EN 45545-2 (European rail fire safety); DMRC / RVNL project specifications |
| Underground station internal wiring | Platform wiring, signalling panel internal, equipment rooms — halogen-free prevents corrosion of signalling electronics during fire | DMRC specification; EN 50121 (EMC), station design codes |
| Data centres & H07Z-K PDU internal wiring | HCl gas from PVC cable fire destroys server hardware; LSZH mandated in most European and ASHRAE-compliant data centres. H07Z-K PDU internal wiring for OEM panel and rack assembly leads. | EN 50173, TIA-942; ASHRAE data centre guidelines |
| Hospitals and healthcare | Patient and staff evacuation safety; medical equipment rooms require zero corrosive gas — smoke will not obscure corridor exit signage | HTM 06-01 (UK NHS); IS 17048:2018 project specifications |
| Airport terminals and underpasses | LSZH wiring mandatory in transit tunnels, baggage handling, and aircraft boarding bridges per airport design standards | DGCA specifications; EN 50575 Construction Products Regulation |
| Switchgear panel internal wiring | Panel manufacturers exporting to EU markets specify H07Z-K for internal wiring to meet the CE / Low Voltage Directive requirements; cleaner burn in panel fire | IEC 61439-1; Low Voltage Directive 2014/35/EU |
| Data Center PDU Feeds | High-current flexible feeds for Power Distribution Units (PDUs); LSZH ensures hardware protection from acidic soot | TIA-942; ASHRAE Data Center Standards |
Where H07Z-K is specified.
Approved H07Z-R stranded infrastructure feeds for FCL/LCL project supply to GCC and East Africa.
The IS 17048:2018 product this is manufactured from.
H07Z-K LSZH building cable — technical questions answered.
Common questions from electrical engineers, safety consultants, and importing partners specifying halogen-free cables for metro, airports, hospitals, and high-occupancy buildings.
What does LSZH (Low Smoke Zero Halogen) mean, and why is it important?
LSZH = Low Smoke Zero Halogen:
- Zero Halogen: No chlorine, bromine, or fluorine in the insulation compound. Unlike PVC cables that emit toxic hydrogen chloride (HCl) when burning, LSZH cables produce zero halogen gas even at high temperatures.
- Low Smoke: Significantly reduced smoke density during combustion — typically 50% less smoke than standard PVC. In a fire, visibility is maintained longer, improving evacuation safety.
Why it matters: In confined spaces (subways, tunnels, aircraft, hospitals), smoke inhalation and visibility loss are the primary fire hazards — not the flame itself. LSZH cables are mandated by building codes and safety regulations in these high-occupancy, low-ventilation environments to reduce fatality risk and preserve escape routes.
What is the difference between H07Z-K, NYM, and FR building cables?
H07Z-K (LSZH): EN 50525-3-41 single-core flexible wire, halogen-free polyolefin insulation. 450/750V rated. Zero halogen gas emission, reduced smoke. Specified for metros, hospitals, aircraft, confined public spaces.
NYM (PVC sheathed): VDE 0281 multicore sheathed cable, PVC insulation and sheath. 300/500V. Standard building cable; uses halogenated insulation. Acceptable for residential and commercial buildings where LSZH is not required.
FR (Flame Retardant): IS 694:2010 single-core wire, PVC with flame-retardant additives. 650/1100V. Slows flame spread but releases dense black smoke and halogen gas. Phase out ongoing; LSZH preferred for new specifications.
Key distinction: H07Z-K is the safety upgrade when environment demands visibility and zero toxic gas emission. NYM is standard commercial. FR is older generation, being replaced.
What are typical applications and markets for H07Z-K?
Mandatory LSZH markets:
- Metro/Rail: Tunnels, stations, train interiors — halogen-free is regulatory requirement in most countries.
- Airports: Aircraft hangars, terminal interiors, ground electrical systems.
- Hospitals & Healthcare: Patient rooms, surgical units, intensive care — life-safety requirement.
- Confined spaces: Submarines, offshore platforms, ventilation-limited buildings.
- High-occupancy public buildings: Shopping malls, theaters, sports arenas over a certain size/height.
European / IEC markets: Germany, Benelux, Scandinavia, UK, Australia often prefer or mandate LSZH for all building wiring as a safety standard regardless of occupancy, driving export demand.
What is the maximum operating temperature and derating for H07Z-K?
Continuous rating: 70°C maximum conductor temperature at 30°C ambient. This is the standard for H07Z-K per EN 50525-3-41.
Short-circuit rating: 160°C for 5 seconds maximum during fault conditions.
Derating factors: Above 30°C ambient, apply temperature derating: typically 0.82 at 40°C, 0.71 at 50°C, 0.58 at 60°C. In conduit or bundled installations, grouping derating also applies — contact for precise tables specific to your cable size and installation method.
Installation: Minimum −5°C for bending/installation; service range −40°C to +60°C depending on cable construction variant.
Enquire for H07Z-K export pricing.
Sizes, colours, reel lengths, export test documentation, and IS 17048:2018 compliance packs — 24-hour response.