[OAC_Sparky]

Blackzx3,

We're really straying off topic, but to summarize, you would never, ever, ever use peak voltage in any horspower calculations, the amount of work done is the RMS.

Peak HP has nothing to do with peak voltage. At all.

Peak voltage is reached on a 120 Hz basis (60 Hz frequency x 2 peaks per cycle). Unless you have a pulsing motor speed (which you could with a variable frequency drive, which doesn't exist in a shopvac), it will never ever produce the "peak horsepower" you suggest because motor speed would have to change 120x a second. Even in a lab.

And because of inductance in the windings it never even makes it to peak.

You can talk about peak values in electronics and audio because you deal with frequencies and capacitance and integrated circuits. But not in inductance motors.

If you're reading this out of a textbook, I think you may have misinterpreted it. Again, no offense):)
Talk to a prof, he should be able to explain it better than I.