On Thu, 1 Jul 2010 12:21:21 -0700 (PDT), Hoosierpopi
wrote:

I was asked today about a motor stamped 240VAC. I kept saying 220
volts and my neighbor would interupt and remind me it said 240 VAC.

I told hm that I didn't think it mattered and that I'd never heard an
explanation of why we see stuff rated at 240 VAC when most of our
homes seem to come standard with 220 VAC and 115VAC.

I've heard 120VAC bandied about and figure those two legs make up the
240VAC.

I told hime that I knew where to post this question having seen days
of posts on similar Electrical (S.O.T. - somewhat off topic) posts
with some folks who appeared to know their stuff providing links to
references and resources.


So, if one og those folks is reading this, please respond and tell me
what gives with the 220 vs. 240 VAC. Can we ignore the minor
difference and usethese motors on "220" or "240?"

FYI - The motor in question did not indicate it was a dual 120/240
voltage motor - it just said 240!

Thanks for reading. Please reply to author.

I'll do my best to simplify the answer.


I think its time for me to explain about 240 current and why it is so
different from 120 volt service. First of all, it's twice as big.
Secondly, it'll shock you more. Outside of that, 240 is really two
120 volt lines coming to your house from different parts of the globe.
The up and down 120 comes from the northern hemisphere, and the down
and up version comes from below the equator.

Without trying to get technical, it all boils down to the direction
water flows when it goes down the drain. In the top of the earth, it
goes clockwise, while on the bottom of the earth it goes counter
clockwise. Since most electricity is made from hydro dams, the
clockwise flow gives you an up and down sine wave, while the
counterclockwise version gives you a down and up sine wave. Between
the two, you have 240 volts, while either individual side only gives
you 120 volts.

This is particularly important to know when buying power tools --
which side of the globe did they come from? If you get an Australian
saw, for instance, it will turn backwards if connected to a US
generated 120 volt source. Sure, you can buy backwards blades for it,
but that is an unnecessary burden. Other appliances, like toasters
cannot be converted from Australian electricity to American
electricity. I knew one person who bought an Australian toaster by
mistake and it froze the slices of bread she put in it.

If you wire your shop with 240 and accidentally get two US-generated
120 volt lines run in by accident, you can get 240 by using a trick I
learned from an old electrician. Just put each source into its own
fuse box and then turn one of the boxes upside down. That'll invert
one of the two up and down sine waves to down and up, giving you 240.
DO NOT just turn the box sideways, since that'll give you 165 volts
and you'll be limited to just using Canadian tools with it.