The current in an alternating current circuit varies continuously in direction and magnitude. Calculations involving the current don't therefore consider the current at any single instant. They instead use the root mean square current, a value that takes into account the current's overall effect. The RMS current describes the current's average strength, disregarding its direction. Diagrams denote this current as "IRMS," with the "RMS" in subscript. A constant level of the root mean square current dissipates the same amount of heat through a resistor as alternating current does.

Determine the circuit's maximum current. This value corresponds with the crest of the current's sinusoidal wave.

Find the square of the maximum current. If, for example, the maximum current is 1.5 amps: 1.5^2 = 2.25.

Divide this squared value by 2. With this example: 2.25/2 = 1.125.

Find the square root of that answer: 1.125^0.5 = 1.06. This answer is the root mean square current.
References
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