XLPE vs PVC insulation: 90 and 70 degree ratings compared

Two compounds, two temperature limits

Most low voltage power cables on a sourcing shortlist use one of two insulation compounds. PVC (polyvinyl chloride) is a thermoplastic: it softens when heated and can be melted again. XLPE (cross-linked polyethylene) starts as polyethylene, but after extrusion it is cross-linked, so its molecules are tied into a network that does not flow back into a liquid when it gets hot. That chemical difference sits behind the two numbers buyers see on every datasheet: a maximum continuous conductor temperature of 90 C for XLPE against 70 C for PVC, and a short-circuit limit of 250 C for XLPE.

These are conductor temperatures, not room temperatures. They tell the project engineer how hot the copper or aluminium may run in normal service, and how hot it may get for a few seconds during a fault, before the insulation starts to degrade. They do not, on their own, tell anyone how much current a cable can carry. That depends on the installation method, grouping, ambient temperature and soil conditions, and it is worked out per installation method to IEC 60364-5-52, BS 7671 or the NEC as applicable, confirmed by the project engineer.

Side by side

The reference values come from a partner plant catalogue and are typical for their categories; the construction for your order is confirmed on the spec sheet. The full LV reference model is on the LV power cables page, and the compound options for every layer are on the insulation and sheaths page.

What the higher temperature buys you

Because XLPE tolerates a hotter conductor, an XLPE cable can generally carry more current than a PVC cable with the same conductor in the same installation. In practice that can mean one size smaller conductor for the same load, or more headroom at the same size. The engineer still checks voltage drop and short-circuit withstand, so the gain is not automatic; on long runs, voltage drop often decides the size whatever the insulation. The cable size selection article walks through the three checks.

The 250 C short-circuit limit matters on larger feeders. During a fault the conductor heats in a fraction of a second, and the cable must survive until the protective device clears it. A higher permitted fault temperature helps the cable pass that check at a given conductor size.

XLPE also has lower dielectric losses and better electrical properties than PVC, which is why every medium voltage cable to IEC 60502-2 uses XLPE (or another cross-linked compound) rather than PVC. At low voltage the electrical difference is less important than the thermal one.

Where PVC still makes sense

PVC remains the normal choice for building wire, flexible cords and control cable. It is easy to process, takes colour well, accepts a clear print and is flexible at the thicknesses used for small conductors. The 60227 IEC 01 family (H07V-U, H07V-R, H07V-K) and the H05VV-F cord are PVC constructions, and so is the KVV-type control cable on our control cables page. For small final circuits the 70 C limit is rarely the constraint.

Some markets also expect PVC power cable by habit or by local standard, for example NYY-type constructions in parts of Southeast Asia. In those cases the decision is a market question rather than an engineering one; the NYY vs CV article covers that comparison for Thai projects.

Sheath, smoke and halogen: a separate question

Insulation and sheath are different layers, and buyers sometimes assume that an XLPE cable is automatically low smoke and halogen-free. It is not. A YJV cable has XLPE insulation and a PVC outer sheath, so in a fire it still releases hydrogen chloride from the sheath. A cable is only LSZH when the sheath, fillers and tapes are halogen-free too, and that is proven by IEC 61034 and IEC 60754 test reports, not by the insulation name. The LSZH sheath article explains those tests.

Flame behaviour is also a cable-level property. Either construction can be made flame-retardant to IEC 60332-1-2 per test report, and in the EU the CPR class declared on the DoP applies to the finished cable, not the insulation compound.

Ageing, quality and how to specify

Insulation compounds fail when the formulation is wrong, not only when the cable runs hot. A widely reported 2013-2014 Australian recall involved building cable whose PVC insulation did not meet ageing requirements: roughly 4,000 km of cable and around 40,000 homes and businesses were affected, according to the ACCC. The problem was the compound, not the conductor size. It is the reason the desk asks for heat ageing and thermal test results in the type test report, not only conductor resistance.

For XLPE, the equivalent check is the degree of cross-linking, usually verified by a hot set test in the type and sample test programme. Poorly cured XLPE behaves more like plain polyethylene at high temperature. A routine voltage or spark test will not reveal either problem, which is why the testing and inspection page lists sample and type test records alongside routine tests.

A clear insulation line on the purchase order reads like this:

1. Compound and rating: XLPE, 90 C conductor rating, or PVC, 70 C.
2. Standard: IEC 60502-1 for 0.6/1 kV power cable, IEC 60227 for building wire and cords, or the national equivalent.
3. Thickness: nominal insulation thickness per the standard, with minimum thickness checked on the sample.
4. Records: routine test records per drum, plus the type test report covering ageing and, for XLPE, hot set.

Send the cable list with those four lines through the quote form; MOQ per size and drum length are covered on the MOQ and lead time page.