What insulation does
Insulation keeps the voltage on the conductor and sets the highest temperature the conductor may run at. That temperature, together with installation conditions, determines how much current a size can carry, which is why the insulation material matters as much as the copper. The two common materials for power cable are XLPE (cross-linked polyethylene) and PVC. XLPE runs at 90 C continuously and tolerates 250 C during a short circuit; PVC is rated 70 C. IEC 60227 covers PVC-insulated cables up to 450/750 V and IEC 60245 the rubber-insulated equivalents; IEC 60502-1 and -2 cover extruded insulation for 0.6/1 kV and medium voltage power cables.
Thickness is set by the standard for each voltage and size. As reference constructions from the partner plant catalogue show, a 0.6/1 kV 4x25 mm2 copper cable uses 0.9 mm of XLPE, a 4x95 mm2 aluminium cable 1.1 mm, and an 8.7/15 kV 3x95 mm2 cable 4.5 mm between semiconductive screens. A 450/750 V 2.5 mm2 building wire carries 0.8 mm of PVC.
What the sheath does
The outer sheath protects against abrasion, moisture, sunlight and installation damage, and it carries the print. Its compound also decides most of the cable's behaviour in a fire. PVC is the default for general use. LSZH (low smoke zero halogen) is specified for public buildings, tunnels and data centres, where smoke and corrosive gas matter. Cross-linked halogen-free compounds are used on solar cable such as H1Z2Z2-K. THHN building wire adds a thin nylon jacket over PVC insulation under UL 83.
| Reference construction | Insulation | Sheath |
|---|---|---|
| 0.6/1 kV Cu/XLPE/PVC 4x25 mm2 | XLPE 0.9 mm | PVC 1.8 mm |
| 0.6/1 kV Al/XLPE/PVC 4x95 mm2 | XLPE 1.1 mm | PVC 2.1 mm |
| 8.7/15 kV Cu/XLPE/CTS/PVC 3x95 mm2 | XLPE 4.5 mm | PVC 2.8 mm |
| 450/750 V Cu/PVC/PVC 7x1.5 mm2 control | PVC 0.7 mm | PVC 1.2 mm |
| 300/500 V 3x1.5 mm2 flexible cord | PVC 0.7 mm | PVC 0.9 mm |
| H1Z2Z2-K 1x4 mm2 solar cable | Cross-linked, halogen-free 0.7 mm | Cross-linked, halogen-free 0.8 mm |
LSZH: what the tests actually measure
LSZH is an industry term, not a promise that a cable makes no smoke. It is proved by three tests per report. IEC 61034 measures smoke density, with light transmittance of at least 60 percent as the usual criterion. IEC 60754-1 measures halogen acid gas, at no more than 0.5 percent. IEC 60754-2 measures the acidity and conductivity of the combustion gases, with pH at least 4.3 and conductivity no more than 10 uS/mm. Flame spread is a separate matter, covered on fire performance classes. Ask for all three reports for the exact construction, not for a different cable from the same plant; more in LSZH sheaths explained.
Medium voltage insulation systems
From 3.6/6 kV upward, the XLPE is extruded between a conductor screen and an insulation screen, both semiconductive, so the electric field is even and free of air gaps. The reference 8.7/15 kV cable adds a copper tape screen over the insulation screen. Every MV drum receives a voltage test, which IEC 60502-2 sets at 3.5 U0 for 5 minutes as a routine test, and a partial discharge test to IEC 60885-3, with sensitivity of 10 pC or less at 1.73 U0. See MV power cables.
How insulation fails, and how it is tested
Insulation problems rarely show on day one. In Australia, a 2013-2014 recall covering about 4,000 km of building cable and about 40,000 homes and businesses was caused by PVC insulation that failed ageing requirements, according to the ACCC; the conductors were not the issue. That is why thermal ageing reports matter as much as routine tests. On each drum the plant runs a spark test on the insulation during extrusion, a voltage test on the finished cable, and measures insulation thickness and overall diameter. Thermal ageing, cold bend and compound tests sit in sample and type test reports.
What changes price, weight and lead time
- XLPE against PVC insulation: XLPE needs cross-linking and is standard on power cable; PVC suits building wire and control cable.
- LSZH sheath: costs more compound per metre and is made by fewer plants, which can affect lead time.
- UV and oil resistant grades: require the right compound and a report; ask before production, not after.
- Thickness: thinner than the standard saves material and fails the dimension check; the desk measures it at inspection.
Send the market, standard and sheath requirement through the quote form; typical MOQ and timing are on MOQ and lead time.