On the AC side of a building, a cable rating is a rough guide and the installation rules finish the job. On the DC side of a PV array, the rating is a set of separate limits that do not move together, and the figure most often quoted in a quotation decides the least. A solar cable carries several numbers at once: 1.5 kV to earth, 90 °C continuously, 120 °C for a limited number of hours, and a service life of at least 25 years outdoors. Buying to one of them and ignoring the rest is how a cable that meets the standard still runs hot.
The DC Side Is Not a Low-Voltage Cable Problem
Three things make it different, and none is voltage on its own.
The current is treated as continuous. The NEC states that PV currents shall be considered continuous, and sizes conductors on that basis.
A DC arc has no zero crossing. Alternating current passes through zero twice per cycle and an arc between separating contacts tends to go out. On DC it does not, so a series fault starting at a poor joint has nothing to extinguish it.
The environment is the installation. Solar cable sits in sun, rain, ozone and temperature cycling for its whole service life, which is why EN 50618 devotes 12 of its 28 pages to tests rather than to construction. Cable is 4 to 5 percent of a project’s cost, and poor selection can affect output for the life of the system.
What the 1.5 kV Rating Covers
Rating | Figure | What it limits |
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DC voltage, conductor to conductor | 1.5 kV | The dielectric between the two live conductors |
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DC voltage, conductor to earth | 1.5 kV | The dielectric between a conductor and any grounded metal |
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AC voltage | 1.0/1.0 kV | Use of the same construction on an AC circuit |
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Continuous conductor temperature | 90 °C | The normal operating limit, with ambient underneath it |
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Peak conductor temperature | 120 °C for a maximum of 20 000 h at a maximum 90 °C ambient | An allowance for extreme days, not a second continuous rating |
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Short-circuit conductor temperature | 250 °C for a maximum of 5 s | Fault survival only |
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Minimum service temperature | −40 °C | Cold impact and handling |
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Storage temperature, IEC 62930 | Up to +45 °C | Warehousing before installation |
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Bending radius | 4 × diameter up to 8 mm; 5 × from 8 to 12 mm | Dressing and installation |
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Conductor | Tinned copper, flexibility class 5 | Corrosion and movement |
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Thermal endurance index at 20 000 h | Not less than 120 | Long-term material capability |
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Water resistance | AD8 submersion | Buried and wet locations |
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Reaction to fire, EU projects | A CPR class such as Cca-s1b,d2,a1 | Construction products obligations |
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The rating is not one dielectric duty. EN 50618 applies to cables on the DC side of a photovoltaic system where there is a nominal direct current voltage of 1.5 kV between conductors and between conductor and earth. IEC 62930, issued in 2017, uses the same pair of conditions.
That wording covers two things: conductor to conductor, and conductor to earth. The second matters more on an array, because frames, rails and tracker structures are within reach of the cable everywhere.
Two dielectric duties, not one
The figure is also a system requirement rather than a cable preference. The NEC caps the maximum voltage of PV DC circuits at 600 V for one- and two-family dwellings and 1000 V for other buildings, and permits 1500 V for listed DC PV equipment not located on or in a building. The cable must be rated at or above the maximum the circuit can reach, and that maximum comes from module open-circuit voltage corrected for the lowest expected ambient temperature.
Ninety Degrees Is a Conductor Limit, Not an Ambient Limit
EN 50618 states that the cables are designed to operate at a normal maximum conductor temperature of 90 °C, but that for a maximum of 20 000 hours a maximum conductor temperature of 120 °C is permitted at a maximum ambient temperature of 90 °C. A note in the same standard gives the expected period of use as at least 25 years.
Both halves matter. The 120 °C allowance has a clock on it: it exists so a cable can survive extreme days, not so it can be operated there. The 90 °C is a conductor temperature, so the ambient sits underneath it and the current comes down as the air gets hotter.
The Current You May Carry Is an Installation Figure
The jacket tells you the conductor limit. It cannot tell you the current you may carry, because that depends on the installation.
A 1 × 4 mm² solar cable from one manufacturer is rated 55 A free in air, 52 A on a surface, and 44 A as two cables adjacent on a surface. The same maker’s 1 × 6 mm² is rated 70, 67 and 57 A on the same three bases. Nothing about the cable changed. The installation did.
Air temperature moves it further. The same datasheet publishes correction factors above 60 °C; grouping is handled separately by IEC 60364-5-52 Table A.52-17.
Air temperature | Up to 60 °C | 70 °C | 80 °C | 90 °C |
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Correction factor | 1.00 | 0.92 | 0.84 | 0.75 |
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The same cable, five currents
On a roof or in a desert field, that last figure removes a quarter of the current before any other correction. Voltage drop appears on the same table and decides the rest.
Size from the manufacturer’s current table, take grouping factors from the governing standard, and treat the jacket rating as the input to that calculation.
Double Insulation, and Why Class II Keeps Appearing
Both standards say the same thing in different words: cable meeting them is suitable for use with Class II equipment, which IEC 61140 defines as protection by double or reinforced insulation rather than by a protective earth connection.
A solar cable has cross-linked insulation around the conductor and a cross-linked sheath over it, and both standards require cross-linked material for both layers. The sheath is the second barrier, not a jacket. A thermoplastic construction of the same dimensions has not passed the same tests.
Why the Conductor Is Tinned
Solar cable conductors are electrolytic annealed tinned copper in flexibility class 5, as IEC 60228 and EN 60228 define.
Neither reason is about conductivity. Tinning is about the twenty-five years rather than the first day: it protects the strands and the termination against corrosion where moisture reaches a crimp. The flexibility class is about installation — pulled through tray, dressed around module frames, and on a tracker, moving with the structure every day. Neither property is visible in a photograph, and neither shows up in a continuity test.
The Test Battery Only Solar Cable Gets
Solar cable is tested for things ordinary cable is not.
Test | What it establishes |
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Ultraviolet chamber, 720 h on a rotating platform | Whether the sheath survives years of sunlight. Elongation at break is measured before and after exposure |
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Ozone exposure | A crack-free result on inspection. Ozone attacks polymer that is under stress |
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Acid and alkaline immersion, 7 days | Resistance to chemical exposure, measured by tensile test after immersion |
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Cold impact at −40 °C | Survival of impact without cracking. Hammer and anvil masses are given in Annex C of both standards |
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Dynamic penetration, 1 N per second | The force needed for a needle to reach the conductor, with a low-voltage circuit that breaks on contact |
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Hot set | That the material is genuinely cross-linked. Partly cross-linked material stretches under load |
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Insulation resistance at 20 °C and at 90 °C | Dielectric performance at operating temperature, not only at room temperature |
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Thermal endurance, index at 20 000 h | Not less than 120 |
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Vertical flame, EN 60332-1-2, 1 kW for 60 to 480 s | Flame propagation and charring height |
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Halogen acid gas, EN 60754-1 and -2 | Acid gas content, plus pH and conductivity of the combustion gases |
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Smoke density, EN 61034 | Light transmittance, greater than 60 percent for a low-smoke construction |
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Two rows are worth more than the rest. Hot set catches a cable built on an under-cured compound, because cross-linking is what the standard is buying. Insulation resistance at 90 °C catches a material that behaves at room temperature and not at the temperature the cable is rated to run at.
Weathering Is a Test Result, Not an Adjective
Resistance to weather is not a marketing word on a solar cable. It is the outcome of the tests above.
Material that is not resistant begins by discoloring, and discoloration is the early indicator rather than the failure. Hardening follows, then brittleness, then cracking of the protective layers. Once those crack, conductors can be exposed, and a conductor touching a frame or a second circuit becomes a flash-over path rather than a fault that clears.
That sequence is why the ultraviolet and ozone tests are written into the standard, and why "UV resistant" on a quotation is worth checking against a certificate.
EN 50618 or IEC 62930
The two standards overlap but are not interchangeable.
EN 50618 is the European standard and the more established. It covers low smoke halogen-free, flexible, single-core cable with cross-linked insulation and sheath at a nominal 1.5 kV.
IEC 62930, issued in 2017, is deliberately broader. It permits a class 2 conductor option, sizes up to 400 mm², multi-core constructions, both halogen-free and halogen-containing products, and a storage temperature allowance up to +45 °C.
That breadth is the practical consequence. An EN 50618 certificate tells you the cable is halogen-free. An IEC 62930 certificate tells you the cable met that standard, which allows halogen-containing constructions, so the certificate alone does not settle the question.
There is a separate European obligation on top of both. Construction products placed on the European market need a reaction-to-fire declaration under EN 50575, typically at a class such as Cca-s1b,d2,a1, with a Declaration of Performance from the manufacturer. The cable standard and the CPR class are two different documents, and a tender usually asks for both.
What the Installation Rules Add
The installation rules look after people. The cable is not the safety device.
The NEC requires DC arc-fault protection for PV systems operating at 80 V DC or greater between any two conductors, and requires that protection to detect and interrupt arcing faults arising from a failure in the intended continuity of a conductor, connection, module or other system component in the DC circuits.
Rapid shutdown works on much lower numbers. Outside the array boundary, controlled conductors are limited to 30 V within 30 seconds of initiation. Inside the boundary the limit is 80 V within 30 seconds, and the boundary is defined as 305 mm (1 ft) from the array in all directions. The NEC also sizes conductors at 125 percent of the calculated maximum current; applying the correction factors as well gives a 156 percent multiplier.
Against a cable rated at 1.5 kV, those figures show where the danger sits: at 30 and 80 volts.
Arc Faults, and Where to Look First
Why any of this matters comes down to one fact: the failure mode is a fire rather than a trip.
BASEC, the British approvals service for cables, cites an IRENA report from 2019 that identified arc faults as the common cause of fire-related incidents, and adds its own framing: a cable arc fault is most often caused by damage, breakdown or contaminants in the dielectric.
Damage first, arc second
Read together, those two statements describe a sequence rather than an accident. The insulation is damaged — by a cut during installation, by abrasion against a sharp edge, by water reaching a termination, or by ultraviolet cracking after years in the sun — and the arc follows. Inspecting for the damage is more productive than inspecting for the arc.
Connector selection and crimping sit in the same sequence and are a subject of their own, not covered here.
What to Ask Before You Order
- Which standard the cable is certified to, and the certificate number, so it can be verified rather than believed.
- Whether the insulation and the sheath are both cross-linked.
- The insulation resistance at 90 °C, not only the figure at 20 °C.
- The air temperature correction factors, and the basis of the current rating.
- Conductor material and class — tinned copper, flexibility class 5 — and the storage temperature allowance, which differs between the two standards.
The Short Version
A solar cable is specified by limits that do not move together: 1.5 kV to earth and between conductors, 90 °C continuously, 120 °C for a limited number of hours, and a service life measured in decades. The jacket gives you the conductor limit; the current you may carry comes from the installation, the ambient and a correction table. The tests behind the standard are what separate a cable that meets it from a cable that looks like one.
We build cable to a stated standard and supply the documentation that goes with it: construction, test reports, and the declaration your market requires. Tell us the standard, the cross-section, the ambient and the installation method, and we will tell you what the construction has to be.
Sources
- BASEC (British Approvals Service for Cables), "Solar Cable Testing" — that solar cable is a DC cable with a rated voltage of 1.5 kV DC and a tin coated copper conductor with cross-linked insulation and sheath; the scope of EN 50618 and IEC 62930, including the extensions IEC 62930 permits and its increased storage temperature up to +45 °C; Class II equipment as defined in IEC 61140; the ultraviolet weathering test in which a sample of the sheathing material is placed in a high-pressure ultraviolet chamber on a rotating platform for 720 hours with elongation at break measured before and after exposure; the observation that non-resistant materials start to discolor as an early indicator and that the insulation may harden, become brittle and crack, creating exposed conductors and a risk of flash-over; ozone resistance testing with the sample required to be free from cracks; acid and alkaline resistance testing by seven days of immersion followed by tensile measurement; cold impact testing in a chamber at −40 °C with parameters in Annex C of IEC 62930 and EN 50618; dynamic penetration testing at 1 N per second with a low-voltage circuit interrupted on contact; hot-set testing to establish the degree of cross-linking; insulation resistance measured at 20 °C and at 90 °C; the IEC/EN 60754-1 and 60754-2 gas and halogen assessments; the IEC/EN 61034-2 smoke density measurement; the IEC/EN 60332-1-2 vertical flame propagation test with a 1 kW pre-mixed flame and an application time of 60 to 480 seconds; the citation of an IRENA report from 2019 identifying arc faults as the common cause of fire-related incidents; the statement that a cable arc fault is most often caused by damage, breakdown or contaminants in the dielectric; and the description of product certification as a three-year cycle with audits and surveillance sample testing several times a year and a certificate publicly listed so that end users can check the mark and download the certificate for tendering — https://www.basec.org.uk/uploads/documents/Brochure-Solar_Cable_Testing.pdf
- EN 50618, cables for photovoltaic systems, published standard preview — the application to cables installed for use at the direct current side of a photovoltaic system where there is a nominal direct current voltage of 1.5 kV between conductors and between conductor and earth; that the cables are designed to operate at a normal maximum conductor temperature of 90 °C but that for a maximum of 20 000 hours a maximum conductor temperature of 120 °C at a maximum ambient temperature of 90 °C is permitted; the note that the expected period of use under normal usage conditions is at least 25 years; that cables complying with the standard are suitable for use with Class II equipment; the thermal endurance temperature index corresponding to 20 000 hours of not less than 120; the insulation resistance table giving minimum values at 20 °C and at 90 °C; the specified insulation and sheath thicknesses by nominal cross-sectional area; and the sections covering code designation, nominal cross-sectional area of conductor and continuity of marking — https://elstandard.se/documents/preview/1592301
- IEC 62930, electric cables for photovoltaic systems, reproduction of the standard’s scope and thermal requirements — the rated DC voltage up to 1.5 kV between conductors and between conductor and earth; the application to single-core cross-linked insulated power cables with a cross-linked sheath; that the cables are designed to operate at a normal continuous maximum conductor temperature of 90 °C with the permissible period of use at a maximum conductor temperature of 120 °C limited to 20 000 hours; the expected period of use of at least 25 years; and suitability for use with Class II equipment — https://www.sowell-solar.com/uploads/2023914135143562.pdf
- Top Cable, TOPSOLAR PV H1Z2Z2-K datasheet, technical brochure and Declaration of Performance — the H1Z2Z2-K designation for a cable TÜV certified to EN 50618 and AENOR certified to IEC 62930; an electrolytic annealed tinned copper conductor in class 5 per IEC 60228 and EN 60228; halogen-free cross-linked rubber insulation and outer sheath per table B1 in Annex B of EN 50618 and IEC 62930; the electrical ratings of 1.5 (1.8) kV DC and 1.0/1.0 kV AC; the thermal ratings of 90 °C maximum conductor temperature with 120 °C during 20 000 hours, 250 °C maximum short-circuit temperature for a maximum of 5 seconds, and −40 °C minimum service temperature; flame non-propagation per EN 60332-1-2 and EN 50399; reaction to fire CPR Cca-s1b,d2,a1 per EN 50575; low smoke halogen free per EN 60754-1 and low corrosive gas emission per EN 60754-2; low smoke emission per EN 61034 with light transmittance greater than 60 percent; minimum bending radius of 4 times the cable diameter for diameters up to 8 mm and 5 times for 8 to 12 mm; impact resistance AG2 medium severity; ozone resistance and UV resistance per EN 50618 and IEC 62930; water resistance AD8 submersion; installation in open air, buried and in conduit; the dimensions and admissible current table giving 55 A free in air, 52 A on a surface and 44 A for two cables adjacent on a surface for 1 × 4 mm², and 70, 67 and 57 A for 1 × 6 mm², with voltage drop figures of 14.3 and 9.49 V per amp per kilometer; the air temperature correction factors of 1 up to 60 °C, 0.92 at 70 °C, 0.84 at 80 °C and 0.75 at 90 °C, with group reduction factors per IEC 60364-5-52 Table A.52-17; the statement that 12 of the 28 pages of EN 50618 cover tests and trials to be carried out on the cable; the observation that cables represent around 4 to 5 percent of a solar project cost but can have a significant impact on power output; the Declaration of Performance issued under EN 50575:2014 and EN 50575:2014/A1:2016 with AVCP system 1+ and notified body AENOR 0099; and the statement that solar plants are designed for 25 years durability with a tribunal considering a useful life of 35 years — https://content.voltimum.com/es/29107/topcable_solar_eng_901003012201002_rooftop.pdf
- NEC 2017 Article 690, reproduction of the article — 690.7 that the maximum voltage of PV system DC circuits shall be the highest voltage between any two circuit conductors or any conductor and ground, with a maximum of 600 V for one- and two-family dwellings and 1000 V for other types of buildings, and that listed DC PV equipment rated at a maximum voltage of 1500 V or less shall not be required to comply with Parts II and III where not located on or in buildings; 690.7(A)(1) that the maximum PV system voltage is calculated from the sum of the module rated open-circuit voltage of series connected modules corrected for the lowest expected ambient temperature; 690.8(A)(1) the sum of parallel-connected PV module rated short circuit currents multiplied by 125 percent; 690.8(B) that PV system currents shall be considered continuous and that circuit conductors shall be sized to carry not less than 125 percent of the maximum currents calculated before the application of adjustment and correction factors, with the note that where both are applied the resulting multiplication factor is 156 percent; 690.11 that photovoltaic systems operating at 80 volts dc or greater between any two conductors shall be protected by a listed PV arc-fault circuit interrupter or equivalent listed system components, and that the system shall detect and interrupt arcing faults resulting from a failure in the intended continuity of a conductor, connection, module or other system component in the PV system dc circuits; and 690.12 rapid shutdown of PV systems on buildings, with the array boundary defined as 305 mm (1 ft) from the array in all directions, controlled conductors outside the array boundary limited to not more than 30 volts within 30 seconds of initiation and controlled conductors inside the boundary limited to not more than 80 volts within 30 seconds — https://pdfcoffee.com/nec-2017-article690-pdf-free.html
