Peter Hogan did a nice job on this question but I think too much
has been written on this subject. Paul touched on the real reason.
Here is a copy:

>For the "power cube" transformer being talked about here, it does
>not make any difference at all, hence the lack of polarizing blades
>on the power plug.
>  But for a larger appliance, say a TV, it makes a BIG difference.
>A TV has a chassis, normally metal, and this is connected to one
>side of the incoming power. If the power plug is correctly inserted,
>then the chassis is
>connected to the neutral (ground) side of the power line, and is at
>ground potential (no shock hazard from the chassis, or any
>controls attached to it).
>  If the power plug is inserted the wrong way 'round, the chassis
>(and any attached controls) are connected to the line (hot) side of
>the AC outlet with the full 120 volts on it. You don't have to be a
>rocket scientist to see the hazards now present....

Take a look at your toaster. It has a two blade power cord. If your
outlet is wired wrong and the toaster has a problem and has a dead
short you will then have 120 volts running on the body of the toaster
just waiting for someone to come along and touch it. After lots of
people were hurt and even killed by their new and improved
toasters and fry pans, ect. The goverment stepped in and said to
all builders to start paying attention to AC polarity. This country
still has many older houses that are not wired correct and people
buy and use power cords that defeat polarity.

Regards,
Gary Wigle

My license is "kb0ni" - I studied under "Doc Hall." He studied under
Mr. Zenier and was in the lab the day Mr. Zenier first tried the
"Zenier" diode. That was many MOONS ago.

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