Question

Why is the voltage amplitude of a 110 volt AC wall socket 155 volts?

Answer 1

The line voltage has crept up over the years, 110, 117, 120, 125 to the point that if some vintage equipment is plugged in, it is stressed. Also remember this is the RMS value and the peak voltage is that value times the square root of 2.

Answer 2

The line voltage has crept up over the years, 110, 117, 120, 125 to the point that if some vintage equipment is plugged in, it is stressed. Also remember this is the RMS value and the peak voltage is that value times the square root of 2.

Answer 3

The wall socket supplies alternating current at 110 V RMS. The peak voltage is, as radar explained, \(110 \times \sqrt{2} = 155.563\) V
I can't vouch for whether or not your line voltages have crept up over the years, but at least this explains why you will measure a peak voltage of \(\pm155\)V.

Answer 4

When they say the voltage of an AC line they are referring to what is called the RMS voltage. (Root Mean Square). This is just a convenient way of referring to the voltage of AC sockets, because it has more meaning. As above, the RMS voltage and peak voltage of a SINUSOIDAL waveform are related by the square root of 2. (VRMS * sqrt(2) = Vpeak)

The number is different for waveforms other than sine waves (i.e. square, triangular, sawtooth, etc).

A good way to think about the RMS voltage is this:

The RMS voltage of an AC waveform is the equivalent voltage of a DC source that would supply the same amount of power to a resistive load.

i.e. if you hooked a 155 peak voltage sine wave up to a 1 ohm resistor, the resistor would dissipate the same power as when you hook up a 110V DC supply.