AC Line Loss Calculator

The power dissipated as heat in a conductor due to its resistance, given by P=I²R. It represents real energy wasted (not delivered to the load) in every current-carrying wire.

Because loss is proportional to the square of current (P=I²R); doubling current means the loss term increases by 2²=4 times, all else being equal.

For a fixed power P=V×I, raising voltage lowers the required current proportionally; since loss depends on I², even a modest voltage increase dramatically cuts transmission losses.

A single-phase circuit has two current-carrying conductors (line and neutral/return); a three-phase circuit has three line conductors, each carrying the same current in a balanced system, so the I²R loss is counted once per current-carrying conductor.

In a perfectly balanced three-phase system, the neutral carries zero current, so it contributes no additional I²R loss; unbalanced loads do cause some neutral current and loss.

Utility transmission lines often target well under 5% loss; building/facility feeders are commonly designed for 1–3% voltage drop (a related but distinct metric), with correspondingly low I²R loss percentages.

Resistance increases with conductor temperature (roughly 0.4%/°C for copper); a heavily loaded, hot conductor has measurably higher resistance and thus higher loss than the same conductor at room temperature.

Use a larger conductor (lower R), shorten the run, increase system voltage (lowering I for the same power), improve power factor (lowering current for the same real power), or balance three-phase loads to minimize neutral current.

Indirectly, yes: a lower power factor means more current is needed to deliver the same real power, and since loss depends on I², poor power factor directly increases I²R losses for a given real power delivered.

Line loss (P=I²R) is the power wasted as heat; voltage drop (V=I×R) is the reduction in voltage seen at the load end. Both come from the same conductor resistance but are different metrics — voltage drop affects equipment performance, while loss affects energy cost.

Use the cable's resistance-per-length rating (from datasheets or standard wire tables) multiplied by the one-way conductor length; see our Wire Gauge / Ampacity Calculator for typical copper and aluminum values.

Yes, DC line loss uses the same P=I²R per conductor (typically 2×I²R for a two-wire DC circuit), without the power-factor or three-phase considerations that apply to AC.

Absolute loss (watts) tells you the wasted energy, but loss percentage relative to transmitted power tells you the relative efficiency of the feeder — a small loss can still be a large percentage on a lightly loaded, undersized circuit.

Yes — I²R loss is exactly the heat generated in the conductor; if it exceeds what the cable's insulation and installation method can safely dissipate, the conductor overheats, which is why ampacity tables (not just loss calculations) set the maximum allowed current.