How to Read Cable Markings: CU/XLPE, CWS, SWA, AWA and LSZH Decoded

01Why Cable Markings Matter — and Where They Stop Being Proof

The printing on a power cable is a fast way to identify the manufacturer, the intended construction, the rated voltage, the conductor size, the claimed product standard and traceability information such as batch and metre marks. What it is not is a universal code. The fields a standard requires on the sheath differ from one cable family to the next, and some standards leave the marking format largely to the manufacturer.

A marking should therefore be read against the applicable product standard and the manufacturer’s technical documentation. For procurement and site inspection, the practical checks are these five:

• Construction: conductor material, insulation, any metallic screen, bedding, armour and outer sheath.
• Voltage designation: for example 0.6/1 kV on a common 1 kV-class cable.
• Conductor size and core arrangement: for example 3C x 70 mm².
• Applicable standard: for example BS 5467 or BS 6724 where the project specifies one.
• Traceability: manufacturer identification, batch or date information, and metre marking where the product provides it.

One caution on the last item. Metre marks are useful for locating positions along a run and for a first check on delivered length, but their accuracy and their marking interval are product- and manufacturer-dependent. Treat them as a check, not as proof of the quantity delivered; for commercial verification, use the manufacturer’s stated marking system together with the drum documentation and, where necessary, independent measurement.

If a project specifies CU/XLPE/SWA/PVC 0.6/1 kV armoured power cable, or a BS 6724 LSZH armoured cable, then the construction and standard printed on the delivered drum should be checked line by line against the purchase specification and the certificate or test documentation.

02How to Read a Typical Cable Marking

Consider this illustrative string. It is a realistic composite, not a prescribed format:

SORIVO  CU/XLPE/SWA/PVC  0.6/1 kV  3C x 70 mm²  BS 5467  2026-06  METRE 000125

The order and the fields vary between manufacturers and standards. The reading below is an engineering shorthand, not a mandatory universal marking sequence.

Table 1 note: the example is illustrative. Marking requirements are product- and standard-specific, and no single sequence is mandatory across all standard families.

03Decoding Cable Construction, Layer by Layer

Most reading errors come from treating the code as a flat list of words. It is better understood as a stack. A full description of a power cable has up to six functional layers, and a code string names some of them while silently omitting others.

• Layer 1Conductor — CU, AL
• Layer 2Insulation — XLPE, PVC, EPR
• Layer 3Metallic screen — CTS, CWS
• Layer 4Bedding / inner sheath — PVC, LSZH
• Layer 5Armour — SWA, AWA, STA
• Layer 6Outer sheath — PVC, LSZH, PE, PUR

Layer 1 — Conductor: CU, AL and Tinned Copper

Table 2 note: IEC 60228 classifies conductors by construction and flexibility — in simplified terms Class 1 solid, Class 2 stranded for fixed installations, Class 5 flexible and Class 6 more flexible again.

Layer 2 — Insulation: XLPE, PVC, EPR, XLPO

Table 3 note: a higher insulation temperature class does not automatically raise the usable current. Ampacity depends on installation method, ambient conditions, grouping and the reference conditions of the rating table — see the cable ampacity and cross-section guide.

Layer 3 — Metallic Screen: CTS and CWS

Between the insulation and the bedding sits a layer that the four-layer shorthand usually forgets: the metallic screen. It is standard practice on medium-voltage cable and appears on some low-voltage designs too. It performs two jobs that armour does not: it shapes the electric field across the insulation, and it provides a defined low-impedance path for earth fault current so that protection can operate quickly.

Table 4 note: this is the layer most often misread. A cable coded CU/XLPE/CWS/LSZH does not necessarily have armour at all — the metallic screen is not the armour. See section 04.

Layer 4 — Bedding / Inner Sheath: PVC or LSZH

The bedding sits between the cores and the armour. Its job is partly mechanical — it stops the armour wires or tapes from bearing directly on the insulation — and partly geometric, because on a multicore cable it also fills the interstices so the assembly is round enough for the armour to be applied evenly.

Table 5 note: the bedding is a distinct layer from the outer sheath. A cable can have a PVC bedding and an LSZH outer sheath, or the reverse, depending on the standard and the manufacturer’s design. Always read the full construction, not one word of it.

Layer 5 — Armour: SWA, AWA and STA

Table 6 note: the armour is normally required to be earthed, both as a fault-current path and to prevent the armour reaching a dangerous potential under fault conditions. Earthing method and gland selection (BW, CW, CX type) form part of the design.

For single-core AC circuits, magnetic metallic armour can produce additional losses and local heating because the alternating field induces currents in the steel. Aluminium wire armour, or another suitable non-magnetic arrangement, is therefore commonly selected. The exact design still has to be checked against the cable standard, the current-rating calculation, the installation arrangement and local regulations. Our SWA vs AWA vs STA armoured cable comparison works through the losses and the application matrix in more detail.

Layer 6 — Outer Sheath: PVC, LSZH, PE, PUR

Table 7 note: the outer sheath is the layer a code string most often names last. It is also the layer most often confused with the bedding — they are separate extrusions.

Why “LSZH” Sometimes Appears Twice in a Code

A string such as CU/XLPE/LSZH/SWA/LSZH looks like a typographic error. It is not. Reading it against the six-layer stack resolves it immediately:

• CU — Layer 1, copper conductor
• XLPE — Layer 2, cross-linked polyethylene insulation
• first LSZH — Layer 4, the bedding or inner sheath between insulation and armour
• SWA — Layer 5, steel wire armour
• second LSZH — Layer 6, the outer sheath

Both non-metallic layers are specified as low smoke zero halogen. This is the standard construction of an LSZH armoured power cable, and the same pattern produces CU/XLPE/LSZH/AWA/LSZH on the single-core version. It also explains a family of search strings we see frequently, where the same letters appear twice in slightly different order — people are copying what is printed on a drum or a datasheet, not mistyping it.

04Screen vs Armour: Two Different Jobs, Two Different Layers

This is the single most common misreading of an LSZH cable code, and it is worth stating plainly:

Table 8 note: construction sequences are confirmed against published manufacturer datasheets, including LSZH single-core MV cable and LSZH screened LV cable.

The practical consequence is simple. When a specification or a search string pairs CWS with SWA, the pair is not a choice between alternatives — it is a question about whether the cable has a screen, an armour, or both. Ask for the construction drawing before quoting.

05IEC Model Designations: N2XRY, N2XRH and the Letters Behind Them

British practice names the construction in English letters — CU, XLPE, SWA, PVC, LSZH. Much of continental Europe, Turkey and the Middle East uses a coded designation instead, and the same cable ends up with two or three different names depending on who is quoting it. This is why a specification written in one system can look unrecognisable when it comes back as a quotation from the other.

Table 9 note: the designation family is used across Europe, Turkey and the Middle East for cable made to IEC 60502-1. The armour is not encoded in the core designation — it must be added separately.

Two points about this table are worth carrying into a procurement conversation. First, the “2X” element signals cross-linked polyethylene insulation, and the trailing letter signals the sheath family — Y for PVC and H for halogen-free. Second, and more importantly, the armouring is not part of the core designation. A quotation for N2XRH and a quotation for N2XRH with SWA are two different cables, and the difference will not be visible in the short code.

06What BS 5467, BS 6724 and BS 7846 Actually Mean

Table 10 note: BS 5467 and BS 6724 cover the same two voltage ratings. The difference between them is the bedding and sheath material system, not the voltage class.

“Booklet armoured cable” — What the Term Actually Refers To

UK buyers frequently use the phrase booklet armoured cable, and occasionally booklet power cable, when they mean an ordinary BS 5467 or BS 6724 armoured power cable. Published distributor guidance lists “booklet power” and “booklet armoured” among the trading names for these cable families, alongside the more common “SWA” and “mains power”.

What we could not establish is the origin of the term. We searched for a formal definition in the standards themselves and in manufacturer technical literature and did not find one that explains why this construction acquired the name. So we will not offer an etymology. What can be said with confidence is the practical point: if a specification, a requisition or a search string says “booklet armoured”, the cable being asked for is in the BS 5467 / BS 6724 armoured power family, and the rest of the requirement should be pinned down in the six layers described above.

07EN 50575 CPR: Why “LSZH” Is Not a Fire Class

A cable marked LSZH is not automatically compliant with any particular building fire class, because LSZH is a description of the material system, not a declared reaction-to-fire performance. In European construction projects the declared performance comes from a different place entirely: the Construction Products Regulation.

Regulation (EU) 305/2011 — the CPR — brought permanently installed power, control and communication cables into a harmonised system, and EN 50575:2014+A1:2016 sets out the reaction-to-fire classification. The requirement has applied since July 2017. Declared performance is expressed as a class from Aca to Fca, qualified by three groups of sub-ratings.

Table 11 note: ca denotes cable. The sub-ratings describe smoke production (s), flaming droplets (d) and acidity of evolved gases (a). They are declared together with the main class as a single string.

The classification is built from four test methods, and knowing which one produces which sub-rating is what allows a declared class to be challenged intelligently:

Table 12 note: the class and its sub-ratings are a single declared performance string, not independently selectable options. The test programme has to cover them together.

Two published declarations make the point better than any description. An LSZH screened low-voltage cable rated 0.6/1 kV is declared Dca-s1,d2,a1. A single-core LSZH screened and aluminium-wire-armoured cable rated 6.35/11 kV from the same family is declared Cca-s1,d2,a1. Both are LSZH cables. They are not the same fire class, because the class is a declared test outcome and the material description is not.

08IEC 60502-1 and the Meaning of 0.6/1 kV

IEC 60502-1:2021 covers power cables with extruded insulation for rated AC voltages of 1 kV (U_m = 1.2 kV) and 3 kV (U_m = 3.6 kV). The three values in the designation mean different things:

• U₀ = 0.6 kV — rated RMS power-frequency voltage between conductor and earth or metallic screen.
• U = 1 kV — rated RMS power-frequency voltage between conductors.
• U_m = 1.2 kV — maximum system voltage for the 1 kV class under IEC 60502-1.

This is more precise than saying “the cable can carry 1 kV”. A voltage rating and a current-carrying capacity are separate design parameters, and the second one is not on the sheath at all.

09IEC Fire and Smoke Standards: Do Not Mix Up the Tests

The IEC fire and smoke standards are frequently quoted as if they were interchangeable. They are not, and a marking reference to one of them should not be read as evidence of another.

Table 13 note: ISO/IEC equivalents are frequently cited under both the IEC and the EN numbering; the EN versions (EN 60754-1, EN 61034-2 and so on) carry the same test content under the European designation.

10How to Verify a Cable When the Printing Is Unclear

When sheath printing is damaged or worn, document-based verification comes first and physical checks follow, restricted to a suitable and de-energised access point.

Table 14 note: the screen row is included because a magnet test will not find a copper screen. Where a screened design is specified, the cut end is the only field check that answers the question.

11Selection Matrix: Match the Code to the Installation

The code follows from the installation requirement, not the other way round. The matrix below maps common installation situations to the constructions they typically produce, together with the item that most often needs verifying before the order is placed.

Table 15 note: constructions shown are typical, not prescriptive. Every row still requires the six-layer restatement, and the rating must come from a calculation for the actual installation conditions.

12Common Cable-Marking Mistakes

Table 16 note: each row corresponds to a question we are asked often enough to treat as a pattern rather than an exception.

FAQ

If a marking, a datasheet and a tender specification disagree with one another, the disagreement is usually traceable to one of the layers above — and it is cheaper to resolve it in an email than on site.

Reviewed by Luo Qiang — Senior Cable Application Engineer, Sorivo
15+ years in industrial and renewable energy cable specification. Experienced in cable specification aligned with IEC standards.

Sources checked for this article

• BS 5467 and BS 6724 scope, voltage ratings, bedding and sheath materials, and the trading names “booklet power / booklet armoured” — Eland Cables cheat sheet (PDF)
• BS 6724 construction, LSZH bedding and sheath, single-core AWA versus multicore SWA, and the comparison with BS 5467 — Cable Services BS 6724 guide
• CU/XLPE/CWS/LSZH 0.6/1 kV construction with copper wire screen and no armour, plus the declared performance Dca-s1,d2,a1 — manufacturer datasheet and DoP
• CU/XLPE/CWS/LSZH/AWA/LSZH 6.35/11 kV single-core construction with both screen and aluminium wire armour, declared Cca-s1,d2,a1 — manufacturer datasheet and DoP
• Construction Products Regulation (EU) 305/2011, the legal instrument behind cable reaction-to-fire declaration — EUR-Lex
• EN 50575 Euroclasses, the smoke, droplet and acidity sub-ratings, and the test methods behind them — CPR and EN 50575 cable reaction-to-fire guide

Related reading

• SWA vs AWA vs STA armoured cable: construction, application and cost under BS 5467 / BS 6724
• Armoured vs unarmoured cable: SWA, AWA and PVC construction guide
• AWA cable UK guide: aluminium wire armour, standards and best practice
• XLPE vs LSZH cable: what actually differs
• Cable ampacity and cross-section guide
• Cable supplier audit guide