How to Choose Power Cable for an Industrial Project

What electrical duty must the cable meet?

Record the rated voltage, phase, frequency, continuous current, starting current and type of load before you look at any catalogue. Motors, transformers, variable-frequency drives and distribution feeders place different thermal and electrical stresses on a cable. Choose a voltage rating that matches the system and its grounding arrangement. Cables rated 0.6/1 kV are low-voltage cables; IEC 60502-2 covers 6 kV (Um 7.2 kV) to 30 kV (Um 36 kV), and IEC 60840 covers above 30 kV up to 150 kV (Um 170 kV).

How do you size the conductor for current, voltage drop and fault?

Insulation sets the temperature limit used in these checks. PVC has a normal maximum conductor temperature of 70 °C and 160 °C under short circuit for up to 5 s. XLPE has 90 °C in normal operation and 250 °C under short circuit for up to 5 s. These values are commonly cited from IEC 60502-1 and manufacturer data.

Continuous current. Corrected ampacity must be at least the design current. Ratings depend on the installation method, so take them from the IEC 60364-5-52 tables or the manufacturer's datasheet for the exact cable. The reference ambient is 30 °C in air and 20 °C for buried cables. At 40 °C in air, the correction factor is 0.87 for PVC and 0.91 for XLPE (IEC 60364-5-52, Table B.52.14). The grouping factor depends on the installation method, so take it from Table B.52.17 rather than using a generic value. Corrected capacity = tabulated capacity × ambient factor × grouping factor × other factors. See the cable ampacity and derating guide.

Voltage drop. IEC 60364-5-52 Annex G (informative) gives 3 % for lighting and 5 % for other uses on a public LV supply, and 6 % and 8 % on a private LV supply. National rules may differ. For a three-phase circuit, a practical approximation is ΔU = √3 × I × L × (R cos φ + X sin φ). The voltage drop calculation guide shows the steps.

Fault current. Use the adiabatic check S = I × √t / k, with S in mm², I in A and t in s, for faults up to about 5 s. The k values are 115 for copper/PVC, 143 for copper/XLPE, 76 for aluminium/PVC and 94 for aluminium/XLPE (IEC 60364-5-54 and IEC 60364-4-43). For example, a 10 kA fault cleared in 0.4 s on copper/PVC gives S = 10,000 × √0.4 / 115 ≈ 55 mm², so the next standard size, 70 mm², is the starting point. For fast fuses and breakers, use the let-through I²t from the manufacturer. The short-circuit rating article covers this in more detail.

In what order should the decisions be made?

Choose the voltage class and wiring method first, the conductor duty second, and the environmental layers third. Reversing that order often produces a cable that matches a catalogue name but not the project.

The basis column names the source to quote. Confirm the standard edition the project specifies before ordering.

• Freeze the design basis before requesting final prices.
• Record every correction factor used for ampacity.
• Check terminal capacity after selecting the conductor size.

How does the installation change the cable?

Open air, conduit, buried soil and crowded trays remove heat differently. Ambient temperature, soil thermal resistivity, burial depth, grouping and nearby heat sources can all reduce allowable current. Armour or conduit may be needed where the cable is buried or exposed to impact.

Multicore cables commonly use steel wire armour (SWA). Single-core AC cables normally use non-magnetic aluminium wire armour (AWA), because steel armour around a single AC conductor causes magnetic losses and heating.

Where glands and enclosures face water or dust, check the IP rating. Under IEC 60529, IP66 is dust-tight and resists powerful water jets, while IP68 means continuous immersion under conditions the manufacturer states. IEC 62444 covers cable glands.

For a cable feeding a variable-frequency drive, symmetrical construction and a shield bonded at both ends reduce common-mode current and EMC problems. They do not fix reflected-wave overvoltage at the motor, which needs cable length limits, dv/dt or sine filters, or inverter-duty motor insulation.

Which materials and fire tests should you specify?

Name every layer in the specification:

• Conductor: copper or aluminium. Class 1 solid and class 2 stranded suit fixed installation; class 5 and class 6 are the flexible classes (IEC 60228).
• Insulation: PVC, XLPE, rubber or a project-specific compound.
• Sheath: PVC, PE or low-smoke halogen-free (LSZH).
• Screen and armour (steel tape or steel wire) when the project requires them.

Fire tests are not interchangeable. IEC 60332-1-2 tests a single vertical cable, and IEC 60332-3 grades bunched cables by non-metallic volume. For LSZH, a commonly used halogen acid gas acceptance value under IEC 60754-1 is 0.5 % (5 mg/g) or less. IEC 61034-2 uses 60 % minimum light transmittance as a common low-smoke benchmark.

What belongs in a purchasable specification?

State the applicable standard, voltage grade, conductor material, number of cores, nominal cross-section, insulation, screen, armour, sheath and required tests. Add drum length, quantity, marking and destination.

If the design is not final, request a technical data sheet before placing the order. Do not approve a cable only from a photograph or a commercial nickname.

Frequently asked questions