XLPE vs PVC Power Cable: The Difference Between YJV and VV

What the code letters actually mean

In the GB/T 12706 naming system the first block of letters describes the insulation, and the last block describes the armour and the outer sheath. YJ stands for cross-linked polyethylene, usually shortened to XLPE. V stands for polyvinyl chloride, or PVC. YJV is therefore XLPE insulated and PVC sheathed; VV is PVC insulated and PVC sheathed. The voltage designation U0/U, normally 0.6/1 kV, is written separately because it is not part of the type code.

A single letter swap looks trivial, but the two materials behave differently under heat. XLPE is a thermoset: during cross-linking the polymer chains are bonded into a three-dimensional network, so the material keeps its shape and its mechanical strength at temperatures where it would otherwise soften. PVC is a thermoplastic: it softens progressively as the temperature rises, which is exactly why its continuous operating limit is set lower. Everything that follows in this article is a consequence of that one difference.

• YJ = XLPE insulation, thermoset, continuous conductor temperature 90 °C
• V = PVC insulation, thermoplastic, continuous conductor temperature 70 °C
• A second V at the end of the code = PVC outer sheath; a 3 in that position = polyethylene outer sheath
• YJV22 = XLPE insulation, steel tape armour, PVC outer sheath
• VV22 = PVC insulation, steel tape armour, PVC outer sheath, and it exists for the same burial duty at a lower rating

Temperature rating: 70 °C versus 90 °C

Continuous conductor temperature is the design ceiling, not an operating target. A YJV cable loaded to its rated current sits near 90 °C at the conductor; a VV cable loaded to its rated current sits near 70 °C. Both are safe if the cable was sized and installed correctly, but only one of them has 20 K of spare headroom before the insulation begins to age rapidly.

That headroom matters most in hot climates and in hot installations. The ampacity tables are built around an ambient of 30 °C in air; every degree above that has to be paid for with a derating factor, and the factor is much less forgiving for a 70 °C cable. At 50 °C ambient a PVC cable keeps 71 % of its tabulated current while an XLPE cable keeps 82 %, and at 55 °C the gap widens to 61 % against 76 %. In a Middle East summer, or on a roof, or inside a sun-loaded steel conduit, that difference alone can force a size step on VV that YJV does not need.

Short-circuit rating: 160 °C versus 250 °C

Under a fault the conductor temperature spikes for a few hundred milliseconds. What limits it is not the steady-state rating but the temperature the insulation can survive for that short time without softening, deforming or cracking. PVC is limited to 160 °C under short-circuit conditions; XLPE is allowed to reach 250 °C.

The practical form of this is the adiabatic short-circuit equation used in IEC 60364-5-54: the minimum conductor cross-section is S ≥ I × √t / K, where I is the rms fault current in amperes, t is the fault duration in seconds and K is a constant that depends on the insulation. For copper conductors K is 115 with PVC insulation and 143 with XLPE insulation. Take a 20 kA fault cleared in 0.5 s on a 0.6/1 kV board: √0.5 is 0.7071, so the requirement is 20000 × 0.7071 / 115 = 123.0 mm² for VV, against 20000 × 0.7071 / 143 = 98.9 mm² for YJV. The next standard size up is 150 mm² for the VV circuit and 120 mm² for the YJV circuit. The same fault, the same board, two sizes apart, and two sizes of copper to pay for.

• PVC: continuous 70 °C, short-circuit 160 °C ≤ 5 s, K = 115 for copper
• XLPE: continuous 90 °C, short-circuit 250 °C ≤ 5 s, K = 143 for copper
• The short-circuit check is independent of the load current and often governs on large feeders
• Ask the switchgear supplier for the actual let-through current and clearing time; do not guess 20 kA

Ampacity per mm²: the same size is not the same cable

The figures below are reference values, not a promise. They apply to a three- or four-core copper cable, a single circuit, installed in free air (installation method E in IEC 60364-5-52), with 30 °C ambient air and the conductor at its maximum operating temperature. Change any of those assumptions and the numbers move; the tables in articles 3 and 4 of this series show how.

Read the table by comparing rows, not by comparing one size in isolation. To carry 100 A continuously you need 25 mm² of YJV (127 A) or 35 mm² of VV (126 A). That is the real comparison, and it is the one that decides the cost. The other thing to notice is that current per mm² falls steeply as the cable gets bigger: 4 mm² YJV carries 42 A, which is 10.5 A/mm², while 95 mm² YJV carries 298 A, only 3.1 A/mm². There is no such thing as a safe current density for copper cable, because the surface area available to lose heat does not grow in proportion to the cross-section.

What the price difference is made of

Two things push YJV above VV. The compound itself costs more per kilogram, and the cross-linking step costs energy and cycle time: the insulated core has to pass through a continuous vulcanisation line, or through a warm water or silane cross-linking process, before the insulation has its final properties. VV skips that stage entirely.

The comparison does not end at the per-metre price, though, because copper is normally the dominant cost in a power cable and XLPE lets you use less of it. A 100 A feeder is 25 mm² in YJV and 35 mm² in VV, and the copper in 1 m of 4-core 35 mm² is about 40 % more than in 4-core 25 mm². The smaller cable is also lighter, easier to pull, fits a smaller gland and takes less space on the tray. On long motor feeders and sub-main runs the material saving routinely cancels most of the insulation premium, and on very long runs it overtakes it. The arithmetic is worth doing before the RFQ goes out.

Where PVC honestly still wins

There are jobs where VV is not the compromise choice but the correct one. The first is any installation where the conductor will never approach 70 °C: light loads, short runs, indoor distribution in a temperate climate, panel wiring and control circuits. If the cable is sized by the protective device and ends up three sizes larger than the load needs, the 90 °C rating is being paid for and not used.

The second is where the whole system is already built around 70 °C. Terminal blocks, lugs, contactors, moulded-case breakers and older switchgear are commonly rated for 70 °C terminations, and in that environment a YJV cable cannot be loaded to its XLPE rating anyway. The third is where the cable must be stripped, re-terminated or modified repeatedly: PVC strips cleanly and forgives rough handling better than a cross-linked insulation. The fourth is price-sensitive work with no thermal headroom problem, where the shorter length means no upsize is triggered by the lower rating.

How to write the requirement into a specification

A specification that says power cable gets whatever is cheapest on the day. A specification that names the standard, the insulation, the voltage designation and the construction gets quoted accurately, and it can be checked on delivery. When you ask for YJV22 or VV22, say which one, and say what it has to withstand.

• Standard and voltage: IEC 60502-1, 0.6/1 kV, or GB/T 12706.1 if the project uses the Chinese system
• Insulation and sheath: XLPE or PVC, and the outer sheath material where it matters for burial
• Conductor: Class 2 stranded copper to IEC 60228, or Class 5 if flexibility is needed
• Armour: steel tape for burial and mechanical crush, steel wire where there is a tensile or vertical load
• Short-circuit: state the fault level and duration the circuit has to survive, in kA and seconds
• Flame and smoke: IEC 60332-1 or IEC 60332-3-24, plus LSZH per IEC 60754 and IEC 61034 where the building type requires it
• Screen: copper tape or copper wire screen where EMC or fault return path matters
• Delivery: drum or coil length, cut lengths, drum marking, and the documents you want with the shipment