- Power Cable Definition: A power cable is defined as an assembly of insulated electrical conductors used for transmitting and distributing electrical power.
- Types of Cables in Power System: Power cables can be overhead or underground, designed for specific applications and requirements.
- Short Circuit Rating: Short circuit rating measures a cable’s ability to handle a sudden surge of current, crucial for safety and performance.
- Current Carrying Capacity: This defines the maximum current a cable can safely carry, determined by the cable’s heat dissipation capabilities.
- Voltage Drop: Voltage drop depends on the conductor material and size, with larger and better-conducting materials like copper experiencing less drop than aluminum.
A power cable is sized and rated for voltage, continuous current, short-circuit current and voltage drop. Overhead lines or buried circuits can both carry the same load. Power cables are the sheathed assemblies used for power transmission and distribution. Each core is one or more individually insulated electrical conductors, usually held together with an overall sheath.
Electrical power cables may be installed as permanent wiring in a building, buried in the ground or run exposed overhead. Flexible power cables feed portable devices and mobile tools.
Power cables are designed from voltage, current and the maximum conductor temperature allowed by the insulation. The duty then sets extra construction such as armour or a UV-stable sheath.
Mining cables add mechanical strength, often with double armour. Wind-turbine circuits need a flexible, UV-stable sheath that can move with the nacelle. Buried circuits avoid storm damage, need less day-to-day inspection and can show a smaller voltage drop than an equivalent overhead span.
Rating of Power Cable
Short Circuit Rating
Conductor size is often set by short-circuit current, not by continuous load. A fault injects a high first-cycle current, then a decaying RMS current until the protection operates. Typical feeder clearance in the original text was 0.1 to 0.3 s. Catalogue 1 s ratings use the IEC 60949 adiabatic method. The table below is that 1 s example for 120 mm2 PVC, not a universal fault current.
| Conductor Size and Material | Insulation Material | Operating Maximum Temperature | Short Circuit Rating |
| 120 sq-mm Copper conductor | PVC Insulation | 70oC | 13.80 KA/SEC |
| 120 sq-mm Aluminium conductor | PVC Insulation | 70oC | 9.12 KA/SEC |
| 120 sq-mm Copper conductor | PVC Insulation | 85oC | 12.48 KA/SEC |
| 120 sq-mm Aluminium conductor | PVC Insulation | 85oC | 8.28 KA/SEC |
Current Carrying Capacity
The continuous current a cable may carry is set by the temperature the insulation can stand. Voltage drop and the short-circuit rating then decide whether a larger section is needed. For a buried cable the limit is the temperature rise from conductor heat against the thermal resistance of the soil, duct or air. The ampere figures below are example two-core PVC values at the stated ambients, not a global rating.
| Continuous Current Rating of (Cables laid singly) | 2 Core × 16 mm2 | 2 Core × 25 mm2 |
| (i) In Ground (Ground Temp 30oC) | 103 A | 131 A |
| (ii) In Duct (Ground Temp 30oC) | 86 A | 111 A |
| (iii) In Air (Ambient AirTemp 40oC) | 94 A | 125 A |
Voltage Drop
Voltage drop from source to load is a further limit on conductor size, alongside heating and short-circuit withstand.
Ohm’s law is V = IR. Copper has a lower resistivity than aluminium, so a copper core of the same section and length has less voltage drop.
Wire diameter also sets voltage drop. A larger section has less resistance than a smaller section of the same metal and length. In American Wire Gauge, a drop of about six gauge numbers doubles the diameter and a drop of about three gauge numbers doubles the area. Power cables are specified in mm2 under IEC 60228. An older metric-gauge habit of writing ten times the millimetre diameter, so 50 gauge for 5 mm, is not that standard.
Construction of Power Cable
A power cable is built from these layers, each doing a stated job:
- Conductor
- Insulation
- Lay-up, for multicore cables only
- Bedding
- Bedding / armouring (if required)
- Outer Sheath
Conductor
The conductor is the current path. Cable makers use copper (annealed tinned ATC or annealed bare ABC) and aluminium for power cables. IEC 60228 / IS 8130 class 1 is solid, class 2 is stranded for fixed runs, class 5 is flexible and class 6 is extra-flexible for cords and welding leads. Nominal size is identified by the 20 C resistance, not by a quality grade.
Insulation
Each conductor is covered with PVC (polyvinyl chloride), XLPE (cross-linked polyethylene) or an elastomer. IEC 60502-1 sets PVC/A at 70 C continuous and XLPE or EPR at 90 C. IS 5831 Type A and Type B are 70 C; Type C heat-resisting PVC is 85 C. Silicone class temperatures follow the elastomer specification, often 150 C.
| Insulation Material | Maximum Operating Temperature |
| PVC TYPE A | 70oC |
| PVC TYPE B | 70oC |
| PVC TYPE C | 85oC |
| XLPE | 90oC |
| RUBBER – EPR IE-1 | 90oC |
| RUBBER – EPR IE-2, EPR IE-3, EPR IE-4, SILICON IE-5 | 150oC |
Cores are identified by insulation colour or by numbers printed on the cores.
Beading (Inner Sheath)
The inner sheath binds the laid-up cores on a multicore cable and beds the armour or braid. Common compounds are PVC ST-1 or ST-2 and elastomers such as CSP SE-3 or SE-4, PCP SE-3 or SE-4 and HOFR or HD HOFR SE-3 or SE-4.
Armoring
Armour is usually galvanised-iron wire or steel strip, laid over the inner sheath. IEC 60502 treats that layer as mechanical protection first. A steel-wire armour can also serve as an earth path when it is sized, terminated and bonded for that duty.
If a core insulation fails and the armour is bonded, fault current can return through the armour. Mechanical strength is the usual reason for specifying it. Mining cables may use a second metallic layer for conductance.
Beading
Annealed tinned copper wire, nylon braid or cotton braid is used here. Braiding adds mechanical cover and can provide an earth path. It flexes more than wire or strip armour, so it is used where the cable must bend.
Outer Sheath
The outer sheath is usually PVC or an elastomer, often the same family as the bedding. It sits over the armour and takes mechanical, weather and chemical wear. Electrical stress is carried by the insulation, not by this jacket.
| Material | Advantages | Disadvantages | Max Operating Temperature |
| PVC | Cheap, Durable, Widely available | Highest dielectric losses, Melts at high temperatures, Contains halogens | 70oC for general-purpose 85oC for heat-resisting purpose |
| PE | Lowest dielectric losses, High initial dielectric strength | Highly sensitive to water treeing, Material breaks down at high temperatures | |
| XLPE | Low dielectric losses, Improved material properties at high temperatures | Does not melt but thermal expansion occurs, Medium sensitivity to water treeing (although some XLPE polymers are water-tree resistant) | 90oC |
| EPR | Increased flexibility, Reduced thermal expansion (relative to XLPE), Low sensitivity to water treeing | Medium-High dielectric losses, Requires inorganic filler/additive | 90oC |
| Paper / Oil | Low-Medium dielectric losses, Not harmed by DC testing, Known history of reliability | High weight, High cost, Requires hydraulic pressure/pumps for insulating fluid, Difficult to repair, Degrades with moisture | 70oC |
Trade talk in India often calls cores above 6 mm2 power cables and smaller cores wiring cables. That split is informal. Product standards are IS 1554 for PVC, IS 7098 for XLPE (Part 1 revised 2025) and IS 9968 for elastomer cables (Part 1 revised 2025). IEC 60502 is the common international counterpart. A cable is specified by voltage grade and nominal cross-section.
