🚀 go-pugleaf

"Bhoot Nath" <deja_bhoot2000@yahoo.com> wrote in message
news:309e7c98.0210011751.51a56500@posting.google.com...
> This is pretty simple question, but at the moment, I can not find a Google
> reference. I know that the residential power supply in North America is
> 120 volts.

True

>
> Q1. Is that 120 volts PEAK of the sine wave, or is that RMS voltage?
>
RMS

> Q2. If I have a sandwich maker listed as "120V, 60Hz, 900W", how much
>     maximum current does it draw? Assuming a 100% resistive load,
>     is it  900 / (120 * alpha)
>
>     where alpha = [ integral of (Sin x)^2, from 0 to pi ] / pi = 0.50
>
> In other words, will the sandwich maker draw 15 amperes of current? If
> that is not correct, how do I compute it?

It depends what you mean by the maximum current.
If you are concerned about wire/fuse ratings they're
rated for RMS current. The sandwich maker is
a purely resistive load, so the current draw is 900 / 120
= 7.5 Amps.

If you really want the instantaneous peak, that will be
1.414 x 7.5 amps. If you want the turn-on peak, that
depends on the temperature coefficient of resistance
of the heating element. My gues is 7.5 Amps is the
number you're looking for.
>
> Q3. How do I go about computing current drawn by other appliances which
> may not be completely resistive?

You need to know the phase angle of the voltage relative
to the current. Divide the current by the Sin of this angle.
If they're in phase, you get I = P/V.
If they're in quadrature, you get
I = P/V / Sin(Pi/2) = Infinity
i.e., you need infinite current for finite power.

Big caveat -- I haven't looked at this stuff for 25 years.

>
> No, this is NOT a homework problem!

What the hell is it then?