Home / Topics / AC Circuits & EM Waves
Wattless current
Intermediate
Current with no average power at 90° phase.
Current with a 90° phase to voltage (in ideal L or C) transfers no average power; energy swaps back and forth with the source.
An ideal inductor draws current but no net power.
Still heats the wires.
In more detail
Wattless current is the component of current that is 90 degrees out of phase with voltage, carrying no net real power. It flows between the source and reactive components, such as inductors and capacitors.
Real-world uses
- Power engineers track reactive current in grid design.
- Capacitor banks supply wattless current locally to reduce grid current.
- Electricians note that reactive current carries energy back and forth without doing useful work, which increases cable heating.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Does wattless current heat wires?
It causes losses due to resistance in cables, even though it delivers no real power.
Why is it called wattless?
Because it does not contribute to the average power delivered.
Is wattless current really useless?
It does not deliver average power, but it is needed to magnetise motors and transformers, so it is necessary.
Related topics in AC Circuits & EM Waves
Quality factor in LCR · Bandwidth · Power factor · LC oscillations · Parallel resonance · Filters