Most AC devicez don't give a hoot about "polarity". They only know the potential between the two leg, and care not if one side is grounded or not.

Only things that have exposed metal (light fixtures, certain electronic equipment) that are not fully insulated from the current carrying conductors require the plug keying to keep the grounded side grounded.

Thanks

Thanks Ron, you splained it beautifully.
I'm just thankful that the Brick didn't
give us his ultimate wisdom, or we'ld
have been her till Christmas. Amen.

Please be nice,

"Why are non-polarized, two-conductor, replacement plugs being sold? What kinds of devices/appliances are they used for?"

Replacing plugs on two conductor appliances without polarized plugs.

Or do you actually mean receptacles?

Using a table lamp as an example, the screw shell is to be electrically connected to the grounded conductor, the Neutral. The ungrounded conductor, the Hot, is to be connected to the built-in switch which in turn sends power to the center bottom contact in the lamp socket. Properly wired and connected with a polarized plug, the lamp assembly would not pose a shock hazard to a child poking a finger into the empty socket if the switch is Off. With a non-polarized plug, it is a 50-50 chance that the screw shell will be energized whenever the lamp is plugged in, no matter whether the switch is On or Off. With a non-polarized plug, or a polarized plug incorrectly connected, a person changing the "bulb" could get shocked as soon as the bulb base touches the screw shell if a finger is also touching the bulb base. Or the aforementioned child could get shocked by direct or indirect contact with the screw shell. Polarized plugs must be installed correctly.
Polarized plugs have a great deal to do with safety for people.

As a kid in Ontario, I'm sure we had two-pronged plugs with lamps with the metal screw shell. Polarised plugs/sockets hadn't come out yet, so I GUESS they had a ground pin - I don't remember getting shocked - except when I put my finger in a light socket!

Evidently there is some confusion about the definition of screw shell. It is possible for the caring to research it on their own.
The screw shell of a lamp socket is the female threaded portion into which the threaded base of the lamp is inserted by turning.

Here is a link that might be useful: Here is help

The reason that I started this thread was because in a recent visit to my father I found that he wanted to replace the plug on his vacuum cleaner with a non-polarzed replacement. I noticed that the original plug was polarized and vetoed the plan.

I guess that I have not been paying much attention to the fact that there are lots of devices that do not have polarized plugs. I have been looking in the past few days and I see that there are many. A week ago, however, If you had asked me I would have said that there are very few if any. My misperception might stem from the fact that in the olden days nothing was polarized and more modern stuff is so I assumed that non-polarized plug equipment was being supplanted rather than a modern option. I can see why a non-polarized plug is desirable since you don't have to pay attention to how it goes into the outlet.

Polarizing the plug and receptacle is a simple way to ensure portable lamps keep the shell on the grounded conductor without major wiring changes (like adding a grounding conductor).

Many other things are double insulated, and require neither a ground nor a polarized plug.

Since two prong lamps do not have a grounding conductor, the risk of touching a live shell is still not all that great.
You have to touch both a hot and a return connection at the same time to be shocked.

A long time ago the chassis of equipment was sometimes connected to the grounded conductor.
That meant if the plug was 'reversed' the chassis was electrically hot.
Old radios, and all sorts of small appliances did this.

"Why are non-polarized, two-conductor, replacement plugs being sold?"

I once asked that question to the owner of my local hardware store because all the 2-prong plugs he had were non-polarized, and he told me that he once carried them, but had to ship them back to the supplier because they didn't sell and he had many nasty comments from clients about their being too complicated to use for nothing.

"A long time ago the chassis of equipment was sometimes connected to the grounded conductor.
That meant if the plug was 'reversed' the chassis was electrically hot.
Old radios, and all sorts of small appliances did this."

Very true. When the "All American 5" tube-type radios were popular, if a knob was removed or lost, the protruding brass control shaft could easily be at line potential.

"if a knob was removed or lost, the protruding brass control shaft could easily be at line potential. "

And now you know why they used plastic knobs.

"Very true. When the "All American 5" tube-type radios were popular, if a knob was removed or lost, the protruding brass control shaft could easily be at line potential."

Now that you mention it, I think I got a shock from a tube radio once.

Excuse me Brick, but most of those old radio knobs
were bakelite. And I suppose you'll come back with:
"Bakelite is a type of plastic". You win Brick,
you win.

You appear to have a real problem.

Sorry to see it so plainly exhibited.

I think the bakelite was mostly phased (pardon the pun) out before the era of the All American 5. Most of the knobs I saw were styrene, sometimes with a brass sleeve inside.