AC foundations
AC current from impedance
- where
- current (A)
- voltage (V)
- impedance magnitude (Ω)
Explain this equation
Works out the current in an AC circuit from the supply voltage and impedance. Ohm’s law for AC.
I is the current, RMS. V is the RMS voltage across the circuit. |Z| is the impedance magnitude, combining resistance and reactance.
Impedance plays the same role as resistance does on DC: volts per ampere. It just includes the effect of inductance and capacitance.
Sense check: 230 V across 23 Ω gives 10 A. Double the impedance and the current halves.
Watch out: using only the DC resistance of a coil will overstate the current. Keep V and I both RMS.
Once the circuit impedance magnitude is known, divide RMS voltage by it to obtain RMS current magnitude.
The phase angle needs separate information about resistance and reactance. A current magnitude alone does not state power factor.
Enter your values to see the result.
Common mistake
Using only resistance in an inductive load.
Limits
Sinusoidal steady state; use matching RMS quantities.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.