[Al Skierkiewicz]

Marshal,
For sinusoidal waveforms, you multiply the RMS voltage by 1.414 to get peak and then the peak voltage times two to get peak to peak. The line voltage is 120 volts RMS at your house but the peak to peak voltage (what you will see on a scope) is 339 volts. The peak voltage is 169 volts and that is why a full wave rectifier in a standard switching power supply has about around 165 volts output. (line voltage peak less the voltage drop across the diodes, common mode filter, etc.) This is also the common primary power supply voltage in line operated TV sets. This is the reason line voltage operated devices have a voltage breakdown in the 500-1kV range. Typical house wire insulation has a 600 volt breakdown rating.