Can aluminium cable be used instead of copper?
The resistivity of aluminium is higher than that of copper, so a markedly larger cross-section is needed for the same voltage drop. You must do your calculation not with ρ = 0.0175 Ω·mm²/m, which applies to copper, but with the resistivity of the conductor you are actually using. In vibrating vehicle installations the creep and oxidation behaviour of aluminium creates additional risk at the connection points.
It is technically possible but not preferred on vehicle and work machine installations; there are three reasons for this.
1. A larger cross-section is needed. In the voltage drop formula ΔU = 2 x L x I x ρ / A, ρ is specific to the conductor. If you apply the copper value of 0.0175 Ω·mm²/m to an aluminium run, you will calculate the drop smaller than it is. Enlarging the cross-section to reach the same drop partly gives back the weight and cost advantage you gained.
2. The connection point is weak. Aluminium creeps over time under pressure; a terminal you tightened comes loose within months. The oxide layer that forms rapidly on its surface is insulating and increases contact resistance. A loosened, oxidised connection heats up and the fault turns out to be at the end, not in the cable.
3. Dissimilar metal contact. When aluminium and copper are in direct contact and moisture is present, galvanic corrosion starts; the transition should not be made without a suitable bimetal lug.
Practical advice: use stranded copper in low-voltage, vibrating, exposed DC installations. Consider aluminium only in a fixed and controlled installation where weight is critical, with suitable lugs and regular torque checks. In every case verify the connections with a voltage drop test under load: a drop above 0.5 V is a connection fault.
The full topic: Installation, redundancy and field continuity