Every power cable is rated with two numbers, U0/U (or U0/U(Um) for medium voltage). U0 is the phase-to-earth voltage the insulation has to withstand continuously, U the phase-to-phase voltage of the network it runs on. A 0.6/1 kV cable is dimensioned so the insulation tolerates a sustained single phase-to-earth fault, which matters in TN systems where one phase can sit to earth before protection operates. Cross into medium voltage and the design changes shape entirely: at 6/10 kV or higher, every core gains an extruded semiconductive conductor screen, an insulation screen, and a metallic screen that carries earth-fault current while keeping the electric field radial.
Voltcore Cable builds both families at its 86,000 m² plant in Yixing, Jiangsu, where 32 lines cover Class 2 stranding, silane cross-linking, triple co-extrusion for medium voltage screening, steel tape and steel wire armouring, and final sheathing without the material leaving the site. That in-house sequence is why orders mixing copper and aluminium sizes, or medium-voltage and low-voltage drums in one container, still load at Shanghai or Ningbo 15-25 working days after deposit. Procurement teams comparing offers are usually choosing between four answers: an unscreened XLPE build for indoor distribution, a steel-tape or steel-wire armoured build for burial and pulling, a screened medium-voltage build for primary distribution, or a PVC build where the load will never approach the conductor limit. Each is covered below with the full construction stack, reference dimensions and test standards, so your engineer can check the numbers before querying.
Cross-linking converts polyethylene from a thermoplastic into a thermoset. Once the molecular chains are bonded into a three-dimensional network the insulation no longer softens and flows when the conductor is overloaded, and that single change lifts maximum continuous conductor temperature from 70 °C to 90 °C and short-circuit withstand from 160 °C to 250 °C for up to 5 s. In practical terms the same copper cross-section delivers 20-25 % more usable current than a PVC-insulated equivalent, which is why XLPE has displaced PVC across almost every new industrial distribution project where loads are expected to grow.
See all 4 XLPE Insulated Power Cable constructions →
Armour is mechanical insurance, and the type you buy has to match the force you expect. A steel tape wrapped in two counter-lapped layers principally resists radial pressure: the weight of compacted backfill, a rock resting on the route, or the crush of a hand excavation tool striking the sheath. It contributes almost nothing to tensile strength. Round steel wires laid helically around the bedding do the opposite: they accept a large axial pull, so they are specified wherever the cable hangs, drops vertically, or must be dragged several hundred metres along a route.
See all 4 Armoured Power Cable constructions →
Above 1.8/3 kV a power cable stops being a conductor wrapped in insulation and becomes a controlled field structure. The difference is the triple extrusion: a semiconductive conductor screen bonded over the stranded copper to smooth out the microscopic peaks between wires, then XLPE insulation, then a second semiconductive screen over the insulation. Those two black layers remove air gaps where partial discharge would start, and without them a cable rated at 6/10 kV would fail within months of energisation rather than decades.
See all 4 Medium Voltage Power Cable constructions →
PVC insulation has not disappeared from low-voltage distribution; it has retreated to the applications where its limits do not bind. It is a thermoplastic, so above roughly 70 °C continuous conductor temperature it softens under compression, and that ceiling is written into IEC 60502-1: 70 °C continuous, 160 °C for up to 5 s under short circuit, against 90 °C and 250 °C for XLPE. The consequence is real and quantifiable, roughly 20 % less usable current from an identical copper section.
See all 4 PVC Insulated Power Cable constructions →
Selection notes — Power Cable
How to size a power cable from load, ambient temperature and installation method
Tabulated current ratings assume 30 °C air or 20 °C ground, a single circuit, and soil thermal resistivity of 2.5 K·m/W. Real sites rarely match. Multiply the tabulated rating by correction factors for ambient temperature, for grouping with other circuits, and for dried-out soil around ducts; a combined factor below 0.7 is ordinary on a crowded tray.
Check voltage drop next. Resistance figures come straight from IEC 60287, but on long feeders the binding constraint is usually drop at the far end rather than conductor heating. A 185 mm² feeder selected on thermal grounds often becomes 240 mm² once the 200 m run to a remote pump house is calculated. Close with a short-circuit check using the adiabatic equation and k = 143 for XLPE-insulated copper at a 250 °C limit; a conductor carrying the load comfortably can still fail a 25 kA/1 s clearing time.
- Send load current, kW and power factor, not just the cable size
- State installation method: tray, conduit, duct bank or direct burial
- Give worst-case ambient temperature and soil conditions
- State available fault level in kA and protection clearing time
- Confirm acceptable voltage drop at the far end of the run
Copper or aluminium conductor: what changes besides the unit price
Aluminium conducts about 61 % of copper on the IACS scale, so substitution is never one-to-one: 50 mm² copper generally becomes 70 mm² aluminium, and 120 mm² becomes 150 mm². The finished conductor is still lighter and cheaper, but the larger section means a bigger gland barrel, a bigger lug and a slightly larger minimum bending radius to respect during installation.
Termination practice decides whether an aluminium feeder survives its first summer. Aluminium creeps under clamping pressure and forms surface oxide within minutes of stripping, so joints need friction-welded bimetallic lugs, antioxidant compound and a specified torque, plus a re-torque roughly six months after energisation. Aluminium earns its keep on long fixed routes with steady loads: site ring mains, rural distribution feeders, substation-to-plant runs and solar park arrays where cable is the dominant cost line.
- Use aluminium where the run is long and trays or ducts are not space-limited
- Specify bimetallic lugs and joint compound on every aluminium termination
- Confirm gland and tray fill before accepting an aluminium substitution
PVC or XLPE insulation: read the 20 °C difference on the datasheet
PVC-insulated power cable is limited to 70 °C continuous conductor temperature and 160 °C during short circuit. XLPE-insulated cable runs at 90 °C continuous and 250 °C for up to 5 s. The difference is not decoration; it flows directly from the current-rating tables in IEC 60502-1, and on the same 120 mm² copper conductor it is worth roughly 20-25 % of usable current.
XLPE additionally carries lower dielectric loss, resists moisture better, and will not soften under overload the way a thermoplastic does. PVC keeps two real advantages: lower material cost at equal size, and an insulation and sheath system that strips faster and bends more easily during termination, which counts on densely packed distribution boards. Voltcore quotes both side by side on request, so the decision is made on ampacity and short-circuit withstand rather than adjectives.
What to include in an RFQ so we can quote within 24 hours
RFQ rounds are usually lost to ambiguity before they are lost on price. A purchase-ready enquiry names the type code, voltage grade, exact core count and cross-section including reduced neutral, conductor class and material, armour type where relevant, sheath compound, and quantity per size with any drum length restriction.
State the standard you must certify against as well. EU projects need CPR reaction-to-fire class data to EN 50575 on top of IEC 60502-1; Australian projects follow AS/NZS 5000.1; Middle East utility tenders commonly add IEC 60754 and IEC 61034 where low smoke is specified. Voltcore supports those documents with ISO 9001 certification alongside CE, TUV Rheinland and SAA approvals.
- Type code, voltage grade, cores × mm², neutral configuration
- Standard of compliance and any project-specific addendum
- Sheath compound: PVC, PE or LSZH, plus UV or anti-termite requirement
- Quantity per size, drum length limit, port and Incoterms
Request pricing across the Power Cable range
Include cross-section, core count, voltage grade, route length and installation method — those five determine price more than anything else on the page.
- Engineer-reviewed before pricing
- Reference drawings issued with the quotation
- Free sample up to free sample up to 5 m