Peak

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Peak

In an AC current, this means the highest value in the AC wave. AC voltage is commonly named by it's RMS value. For example, the 120V coming out of a standard wall plug would equal 120V DC if rectified/smoothed, so we name it "120VAC" (the RMS value). However, it is important to know that the voltage at times is actually much higher than the RMS. In fact, 120V's peak would be 170V.

The peak value is found by taking the RMS of a sine wave (we'll use 120V) and multiplying by 1.414.

$120 V * 1.414 = 169.68$ (or approx. 170V)

A more accurate factor to use would be $\sqrt{2}=\frac{1}{\sin(45^\circ)}\approx 1.4142135623730950488$