Re: AC polarity

[David Dockstader <DRDOCK00@UKCC.UKY.EDU>]

On Sat, 06 Jul 1996 08:47:22 -0500 Chris Clayton said:
>        My follow-up question would be:  "What's the difference?"  I can see
> how two speakers connected the two ways would be out of phase with each
> other and give destructive interference.  But why does it matter to my
> electric pencil sharpener or my box fan which way the plug goes in?
One place where it matters is with devices that are internally grounded.
Since all houses are supposed to be wired with the same slot connected to
ground, some appliances, rather than using a third wire connected to the
round ground terminal, just use two wires and connect the one that is susposed
to be the house ground to the case or chasis of the appliance.  This is very
common with hand tools.  If you now stick the plug in backwards reversing the
polarity, the case is hot.