Impedance

Impedance is the opposition an AC circuit, cable, winding or device presents to current flow. IEC (International Electrotechnical Commission) Electropedia defines impedance in sinusoidal conditions as the ratio of voltage to current, with resistance and reactance as its main parts, and gives the coherent SI (International System of Units) unit as the ohm. In home energy documents the word usually appears as part of a specific measurement or fault context, such as earth fault loop impedance on electrical certificates, grid impedance in inverter fault messages or equipment impedance in technical data. A lower or higher impedance value only makes sense with the circuit, frequency, test condition and limit it belongs to; it is not by itself a verdict on safety, compatibility, DNO approval or MCS certification.