The conductivity difference
Annealed copper is the reference material for conductor performance, rated at 100% IACS (International Annealed Copper Standard). EC-grade aluminium sits at roughly 61% IACS — it conducts about six-tenths as well for the same cross-sectional area.
That single number drives every other trade-off. To carry the same current at the same temperature rise, an aluminium conductor needs roughly 1.6 times the cross-sectional area of a copper one. In practical terms this usually means going up one or two standard sizes.
| Property | Copper | EC-grade aluminium |
|---|---|---|
| Conductivity | 100% IACS | ≈61% IACS |
| Area for equal current | Reference | ≈1.6× larger |
| Density | 8.9 g/cm³ | 2.7 g/cm³ |
| Weight at equal ampacity | Reference | Roughly half |
| Cost per ampere | Higher | Lower |
Where aluminium wins
Aluminium is about one-third the density of copper. Even after upsizing for the conductivity gap, an aluminium cable of equivalent ampacity weighs roughly half as much. On long distribution runs that changes what the cable tray, the drum handling and the installation crew have to cope with.
Cost follows the same logic. Aluminium is cheaper per kilogram and the finished cable is lighter, so cost per ampere-metre is consistently lower. For LT and HT distribution feeders, incoming service cables and larger cross-sections, aluminium is the routine choice across Indian distribution networks.
- Long distribution feeders where cable cost dominates
- Larger cross-sections, typically above 25 sq mm
- Overhead lines and utility distribution
- Service entrance and incoming supply cables
Where copper is worth the premium
Below about 16–25 sq mm the physical size penalty of aluminium starts to outweigh its cost advantage, and the conductor becomes awkward to terminate in compact enclosures. Copper is also more tolerant of vibration and repeated flexing, which matters for equipment tails and machinery connections.
- Small cross-sections and final sub-circuits
- Panel internal wiring and control circuits
- Machinery, motors and equipment connections
- Installations with vibration or repeated flexing
- Space-constrained routes where the larger aluminium size will not fit
Terminations decide reliability
Most aluminium cable failures are not conductor failures. They happen at the joint, and they are avoidable.
Aluminium forms an oxide layer on contact with air almost immediately, and that oxide is a poor conductor. It also creeps — under sustained clamping pressure the metal slowly deforms, and a joint that was tight at commissioning can loosen over months, raising resistance and generating heat.
- Use bimetallic lugs where aluminium meets copper busbar or terminals
- Clean the oxide layer immediately before termination
- Apply the specified anti-oxidant compound
- Torque to the manufacturer specification — not by feel
- Re-check torque after the first thermal cycles
Direct aluminium-to-copper contact sets up galvanic corrosion in the presence of moisture. A bimetallic lug is not optional at that interface.
Making the decision
For most projects the split falls out naturally: aluminium for distribution and larger sizes where cost and weight dominate, copper for smaller sizes, control wiring and anywhere terminations will be disturbed or subject to vibration.
The one case that deserves a calculation rather than a rule of thumb is a long run near a size boundary. Upsizing aluminium to meet a voltage drop limit can erase its cost advantage, and at that point copper at the smaller size may be both cheaper installed and easier to route.
Conductor requirements for both materials are covered by IS 8130. Confirm conductor class and resistance limits against the current standard and the manufacturer data sheet before ordering.