DC & PV Cable Manufacturers in China: What a TÜV/UL Factory Audit Actually Covers

01“Approved” by whom: certificate scope against certificate logo

Every certification database in the world is built on the same four facts, and a certificate is only meaningful when all four are read together: who holds it, which product and which model range it covers, which standard at which edition was applied, and what type of approval was issued. A logo on a quotation or a website does not carry any of them. It is a picture.

The public TÜV Rheinland database gives a clean worked example, because the fields are visible to anyone with the certificate number. Certificate R 50470504 is held by Guangdong Cable Factory Co., Ltd. The certified product is described as “Cables / Wires (Electric Cables for Photovoltaic Systems)”, the model designation is H1Z2Z2-K 1X2,5...6,0mm², the fulfilled standard is EN 50618:2014, the certificate type is TÜV-Mark Approval / Type Approval, and the date of issue is 2020-06-09.

Four lines on that page are the ones a buyer rarely reads, and each of them limits what the certificate can be used for.

• The standard list is frozen at issue. The page states that the standards listed reflect the status at the time of the certificate's release. A certificate issued against an edition that has since been superseded is not wrong; it is simply a statement about an older document.
• A change to the product voids it. The page states that the validity of the certificate expires if changes are made to the product. A cable reformulated in 2023 is not covered by a 2020 certificate unless the certificate was updated.
• Type Approval is a component-level approval. The explanatory note says the mark is usually awarded for components that are not ready for use and are intended to be incorporated into finished products: the tests focus on the safety of each component. That is a different statement from “this finished cable is approved for your installation”.
• The model range is part of the scope. A certificate covering 2.5 to 6.0 mm² says nothing about a 10 mm² or a twin-core construction, even if the same factory makes it to the same standard.

02What a DC/PV approval covers: EN 50618, IEC 62930 and UL 4703

The photovoltaic cable world is governed by three documents that are often treated as interchangeable in quotations, and are not.

IEC 62930:2017 is the international cable standard for the DC side. Its scope covers single-core cross-linked insulated power cables with a cross-linked sheath, for the DC side of PV systems, at a rated DC voltage up to 1.5 kV between conductors and between conductor and earth. It explicitly covers both halogen-free low-smoke cables and cables that may contain halogens, and the cables are intended for use with Class II equipment as defined in IEC 61140. The normal continuous maximum conductor temperature is 90 °C, with a permitted period at 120 °C limited to 20,000 hours, and the standard notes an expected period of use of at least 25 years. The edition in force was published on 13 December 2017.

EN 50618 is the European counterpart, and it is the one most quotations actually mean. BASEC describes it as the most commonly used solar cable standard, relevant to all low-smoke halogen-free, flexible, single-core power cables with cross-linked insulations and sheaths. The same source notes where IEC 62930 is broader: it permits a Class 2 conductor, larger sizes, multi-core constructions, designs containing halogens and higher storage temperatures. That difference has a direct commercial consequence. A cable built to an IEC 62930 design with a Class 2 conductor, or with halogen-containing materials, can be fully compliant with the standard it claims and still fail a specification written around EN 50618.

UL 4703 is the North American photovoltaic wire standard. It is a separate qualification route: a cable qualified under EN 50618 or IEC 62930 is not thereby qualified under UL 4703, and the reverse also holds.

Scope statements for IEC 62930 from the IEC record and the standard's own clause 1; the EN 50618 description and the comparison with IEC 62930 from BASEC's technical page on solar cabling. The three documents also differ in their type-test regimes, so a test report against one is not evidence against another.

03Conductor check: tinning, strand class and DC resistance

Conductor claims are the easiest to state loosely and the easiest to verify precisely, because IEC 62930 sets them out in short, checkable sentences. There are three of them, and an auditor should be able to walk from the claim to the evidence for each.

Three conductor requirements that are written as rules, not recommendations

• Material and plating (clause 5.1.1). The conductors shall be copper and in accordance with IEC 60228. The wires shall be tin coated, and the tin coating shall form a continuous layer — there shall be no visible gaps in it when examined with normal or corrected vision. Note the wording: it is a requirement about the individual wires, not about the conductor as a whole.
• Strand class (clause 5.1.2). The class of the conductor shall be Class 5 in accordance with IEC 60228 for cable that is directly connected to PV modules. Class 2 conductors are allowed only for cables intended for fixed installation and not directly connected to the PV modules. This is the single most useful sentence in the standard for a buyer, because it converts “flexible copper” into a boundary: a stiff Class 2 conductor on a module lead is outside the standard's requirement.
• Verification (clause 5.1.4). Compliance with the material, construction and separator requirements, including those of IEC 60228, is checked by inspection and by measurement — that is, by counting strands and measuring them, and by measuring resistance, not by reading a certificate.

The measurement worth asking for is maximum DC resistance at 20 °C per unit length, and it is worth checking it against the strand structure the supplier has quoted, because the two must agree. Take a 4 mm² PV conductor built as 56 strands of 0.285 mm. The metallic cross-section is 56 × π/4 × 0.285², which is about 3.57 mm². At the resistivity of annealed copper, 0.017241 Ω·mm²/m at 20 °C, that gives roughly 4.83 Ω/km, and tinned copper is allowed a couple of percent more on top of that, which lands at about 4.9 Ω/km. Our own published figure for that construction is 4.97 Ω/km per core, which is consistent with the strand count rather than merely asserted alongside it. A quotation that states a resistance figure without a strand structure, or a strand structure without a resistance figure, has given the auditor nothing to check.

Requirements from clauses 5.1.1 to 5.1.4 of IEC 62930 (clause 5.1.3 covers the optional non-metallic separator, which must itself be halogen free in a halogen-free low-smoke cable). The resistivity and cross-section arithmetic in the paragraph above is ours and is reproducible from the strand count and the standard resistivity of annealed copper at 20 °C.

04Compound and sheath: what the data sheet will not tell you

The insulation in a PV cable is a cross-linked compound, and IEC 62930 requires that it fulfil the material requirements set out in Table B.1 of its Annex B. Our library holds the standard's construction clauses but not that annex table, so what follows describes the requirement and how it is demonstrated rather than quoting material values.

The standard also fixes how the compound is applied. Insulation is applied by extrusion so that it fits closely on the conductor, while still being removable without damage to the insulation, the conductor or the tin coating. It may be applied in a single layer or in several non-separable layers, and where more than one layer is used, all testing is done on the complete insulation as if it were one layer. A note in the standard adds the point that insulation applied in more than one layer does not conform to the definition of “double insulation” used in IEC 61140. That note matters commercially, because “double insulated” is a phrase that appears in marketing copy for cables that have two extruded layers rather than two independent insulations.

The 25-year and 90 °C claims rest on a defined test basis, and the standard's own reference list says which. IEC 62930 lists IEC 60216-1 and 60216-2 among its normative references — the thermal endurance series that defines ageing procedures and how the results are evaluated. BASEC describes the mechanism: thermal capability is assessed by that series, and the rate of ageing is calculated through physicochemical models, specifically the Arrhenius equation. The same reference list carries IEC 60068-2-78 for damp heat steady state, which is the environmental counterpart to the thermal ageing claim.

What a data sheet will usually not tell you is the part an auditor has to ask for. The compound grade and its supplier; the cross-linking route and the gel content that proves it; the UV stabiliser package and its loading; whether recyclate is present; whether the sheath compound is the same material as the insulation. None of those are secret, and a supplier who works to the standard has them on file. A supplier who cannot name the compound grade is describing a generic construction rather than a qualified one.

05Routine test records: the three lines to read

IEC 62930 separates its tests into three categories, and the distinction is the key to reading any test schedule. A type test is carried out before a cable type is supplied on a general commercial basis, and need not be repeated unless the materials, design or manufacturing process change. A sample test is carried out on samples of completed cable or components taken from completed cable. A routine test is carried out on all production cable lengths, to demonstrate the integrity of each one.

For a buyer, only the third category answers the question “what was done to the cable that is on this drum”. Three lines in a routine test record do most of that work.

1. Spark test on the insulation

A high-voltage electrode scans the full length of the finished core as it runs. It is the only 100 % check for pinholes, contamination and thin spots in the insulation, and it is why the standard lists the spark-test method, IEC 62230, among its normative references. A test schedule with no spark-test line is a schedule that has skipped the one check applied to every metre.

2. Voltage withstand and insulation resistance

The completed length is subjected to an AC withstand test, and insulation resistance is measured in water. Prysmian's PV cable data sheet itemises the set it runs under the HD 22.2 regime: conductor resistance, AC and DC test voltages, electric strength, surface resistance, spark test on insulation, and insulation resistance measured in water at 20 °C and 90 °C, with a further reading in air at 120 °C as an internal test. Our own published figure for our H1Z2Z2-K range is a 6.5 kV AC dielectric test and a 10 kV AC spark test on each batch — stated here as our own factory figure rather than as a standard value.

3. Conductor resistance and dimensions

Resistance per unit length, plus the measured insulation and sheath thickness against the specified values. IEC 62930 puts the thickness requirement in a form worth quoting, because it is not a single number: the average of the measured values, rounded to 0.1 mm, must not be less than the specified value, and the smallest value measured must not fall below 90 % of the specified value by more than 0.1 mm, expressed as tm > 0.9 ts − 0.1, where tm is the minimum thickness at any point and ts the specified thickness. A supplier reporting only an average is reporting half of the requirement.

Finally, a record sheet is only worth what it can be tied to. Date, machine identifier, drum or length identifier, test voltage, measured value and operator signature are what connect a record to a delivery. A photocopied page with no drum reference and no date proves that tests happen at the factory, not that they happened to your order.

06Red flags in a Chinese DC/PV cable quotation

These are the patterns that recur when a DC or PV cable quotation is checked against the record. None of them is proof of bad faith; each is a question that should be answered before an order is placed.

• The certificate number resolves to a different model range. A certificate covering a 2.5–6.0 mm² single-core range does not cover the 10 mm² or the twin-core item being quoted.
• “TÜV approved” with no number. Without a number there is nothing to look up, and the four facts in section 01 stay unknown.
• The standard list predates the current edition. A certificate issued in 2020 that names only EN 50618:2014 is a statement about that edition; ask whether the certificate has been updated since.
• EN 50618 claimed for an out-of-scope construction. A halogen-containing or Class 2 design belongs to the IEC 62930 scope, not the EN 50618 one. Seeing the two used interchangeably is a sign the scope has not been read.
• “Double insulated” used as a synonym for two extruded layers. IEC 62930 explicitly notes that multiple non-separable layers do not meet the IEC 61140 definition of double insulation.
• No conductor resistance figure, or one without a temperature. Resistance without a reference temperature cannot be compared to anything.
• No spark-test line in the test schedule. The 100 % check is missing, and the omission is usually deliberate rather than accidental.
• A 25-year life claim with no ageing basis named. The claim should be traceable to a thermal endurance evaluation, not to a marketing sentence.
• Temperature quoted as a single merged range. Ambient limit and conductor limit are different numbers; a quotation that runs them together has either not measured them or is hiding one.

07What this article covers, and what it will not sign off

Two boundaries belong at the end of an audit article, and both are working limits rather than disclaimers.

The first is evidential. Our library holds the construction clauses of IEC 62930 and the scope statements of the other documents cited here, but not the full text of every standard referenced, and not the material tables in its annexes. Where the text is not in front of us we name the standard and describe the requirement rather than printing a clause number or a table value we cannot show you. The same applies to UL 4703 and to the thermal endurance series: they are named here as standards, and referenced as the basis of a claim, not quoted line by line.

The second is about who issues conclusions. We are on the supplier side of this audit, and this article describes what we have to be able to produce when a buyer asks. We do not certify anyone, we do not declare another manufacturer's certificate invalid, and we do not issue compliance opinions for a project. Our own published position is on our product pages: the H1Z2Z2-K range is qualified to EN 50618:2014 with IEC 62930 and carries TÜV Rheinland certification, and we do not claim UL 4703 for that range. Where a project specifies UL 4703, the honest answer is to say so at the quotation stage rather than to let the specification assume it.

The practical summary is three questions. Which document, at which edition? Which construction, at which conductor class and which model range? And which record from which drum? A supplier who can answer all three without going away to check is a supplier whose paperwork was already in order.