What is the relation between peak current and effective current of an AC power system generated by commercial power companies in the US?

Answer 1

The effective current is the square-root of the average value of the current-squared, root-mean-square or rms for short. That is because the power in a resistive load like a water heater is proportional to the square of the current.

The rms voltage of an ac supply gives the same heating effect as a dc supply of the same voltage.

The peak current is sqrt(2) times higher.

The rms voltage and current are always quoted when referring to an ac power supply.

Answer 2

The situation is basically the same in the U.S. and anywhere else. Power is provided as an AC current; if you graph this current versus time, it basically has the shape of a sine wave.

Effective power is calculate as RMS - meaning root-mean-square. That is, the current at any moment is squared, the average is taken (using an integral), and the square root of the result is calculated.

In the case of a sine wave, RMS (i.e., effective) voltage, or current, is less than the peak voltage, or current, by a factor (square root of 2). As an example, if your home gets its electrical energy at a nominal voltage of 220 volts, that refers to RMS voltage; the peak voltage in this case is about 311 volts. Note that different countries and regions have different nominal voltages, so the above is just an example. However, the factor (square root of 2) should apply equally in other places.