Quote:
When you are dealing with an appliance with a two prong figure-of-eight plug then polarity clearly doesn't matter, as you are free to plug it in any way around, but of course those devices aren't earthed.

Quote:
If bunches of related equipment, say computers & attached (USB, Firewire, DVI-D, etc.. ) accessories, all use polarized wiring, then their PSU's will be in phase and maybe that means they'll have lower interference/emissions or some such thing -- pure speculation on my part.

Quote:
People are thus far less likely to accidently burn/electrocute themselves when changing bulbs.

Quote:
I'm just wondering what the point of polarizing an ungrounded AC power source is.

Quote:

Quote:
People are thus far less likely to accidently burn/electrocute themselves when changing bulbs.

So you're saying that touching one of the prongs will electrocute me, while touching another prong would be harmless?

How is that possible in an ungrounded AC system?

Quote:

Ahh.. One side of your single-phase AC power soure *is* grounded at the source, meaning it literally is connected to the dirt outside your house. The other side is the actual AC supply, known as the "hot" or "live" wire. Only one of the two wires is hot.

Quote:

Here's your homework for tonight: Get out your trusty old voltmeter, set it to the 200VAC range, and stick one probe into some moist earth in your yard, and the other probe into the hot spade socket of an electrical outlet (that's the right-hand side one of a 3-prong outlet when the round prong hole is on the bottom).

Cool, eh? Tell us what voltage you measured. I'll go out and do it here right now.. gimmeasec..

Here ya go. Red probe plugged into a single (hot) conductor of a 120VAC outlet, and black probe just stuck into the wet earth outside our house. You can read the meter voltage..

Quote:

Here ya go. Red probe plugged into a single (hot) conductor of a 120VAC outlet, and black probe just stuck into the wet earth outside our house. You can read the meter voltage..

A variation on that experiment may also be instructional.. take a table lamp outside, and wire it with only one conductor going into the hot side of an outlet, and the other conductor stuck into the ground (do this with it switched OFF!!). Then turn on the switch, and watch what happens..

For an older home, the light will probably illuminate nice and bright.
With a newer home, probably nothing will happen.. can you guess why?

Quote:

Get out your trusty old voltmeter, set it to the 200VAC range, and stick one probe into some moist earth in your yard, and the other probe into the hot spade socket of an electrical outlet (that's the right-hand side one of a 3-prong outlet when the round prong hole is on the bottom).

Cool, eh? Tell us what voltage you measured.

Then repeat the experiment, connecting the voltmeter to the neutral socket instead of the hot socket on the outlet. It will measure 0.0V --> that's the one you can safely lick, if (like Bitt) you're into that sort of thing.

Quote:
One purpose of the polarized 2-prong plugs is to allow devices that would otherwise have required a heavier 3-prong cord to use "double-insulated equivalency" construction along with the 2-prong plug.

Quote:
Very good explanations.

Cool that you got your shoes to light as well.

I hope you didn't get them dirty. The wife will be mad.

Quote:
Effectively, it's not that the hot wire forces electricity for 1/60th of a second and then the neutral wire does, it's that the hot wire forces electricity for 1/60th of a second and then sucks it back for 1/60th of a second.

Just being nit-picky, but the period of the sine wave is 1/60th of a second- that's push + pull.

Quote:
No, the main reason is so that an internal short will go to ground.

Quote:

Your chandelier example is a fine example of this. The chandelier was designed so that the neutral connector was connected to the metal body of the chandelier. This is required by electrical code (or some other law -- who

Quote:
The purpose of polarization is to allow things like switches to be connected to the correct wire, so that when "off", there is no hazardous voltage present in the product beyond the switch. And etc..

Quote:

So then why do things seem to work fine no matter which way I plug in the device? Why aren't old style plugs (or the English plugs) polarized?

Quote:
If bunches of related equipment, say computers & attached (USB, Firewire, DVI-D, etc.. ) accessories, all use polarized wiring, then their PSU's will be in phase and maybe that means they'll have lower interference/emissions or some such thing -- pure speculation on my part.

Quote:
Why aren't old style plugs (or the English plugs) polarized?

Quote:
But they are polarised?

Quote:
Ah, right. He was talking about the figure of 8 "radio cassette" leads. No matter what mains connector you fit at the plug end, they are reversible at the appliance end.

Quote:

With a newer home, probably nothing will happen.. can you guess why?

And for a really new home (with an RCD) all your lights and computers will go off and you'll have to reset your clocks and....

These Residual Current Devices replace the main (or sub) fuses/circuit-breakers and work by 'measuring' the current flowing into your house on the live wire and the current flowing out of your house on the neutral. If they don't match to within a few mA (typically 30), they trip. So any attempt to light bulbs using the live->earth->electric company loop will fail

Actually that's a 'cos anyone who's been miswiring plugs (or dremelling them down <shock>) will still not kill any innocent bulb-changing house guests who happen to be standing in the kitchen sink (Canada is a strange place...)

I must admit we have a lot more respect for the mains over here in the UK - I don't know anyone who would *dream* of doing what Tony did to a plug. Maybe the added lethality/pain of the 240V instils more caution?

As an aside - the RCDs do have a drawback - because the house circuit breakers only switch live and the neutral and local earths always have a slightly different potential you do get a tiny current flow if you short neutral to earth. So when you're rewiring bits of the house (eg changing wall sockets) you can still trip the main RCD if you brush the neutral against the earth *even after isolating the circuit at the fusebox*. This is much more annoying than a slight belt from touching the live with your fingers and weirdly leads to a far more bomb-disposal-like approach when you're threading the non-live wires throught the metal back-boxes etc..

Quote:
it ensures that the outside screw conductor of a standard light bulb socket will not be connected to the hot voltage wire.

Quote:
I must admit we have a lot more respect for the mains over here in the UK - I don't know anyone who would *dream* of doing what Tony did to a plug. Maybe the added lethality/pain of the 240V instils more caution?

Quote:

Even the screw fit ones tend to have a plastic shell on the outside, so you have to put your finger in the fitting.

Quote:

Quote:

With a newer home, probably nothing will happen.. can you guess why?

And for a really new home (with an RCD) all your lights and computers will go off and you'll have to reset your clocks and....

... Residual Current Devices ...

Quote:
Most homes here have per-circuit devices (or even just per-outlet) that are required by code in certain rooms (eg. bathroom) and on outside (the building) circuits.

Quote:
Actually, a GFCI outlet will also protect any "downstream" outlet, too. Can be a pain when something trips and you have to wander all over the house trying to find which GFCI needs resetting. Less of a pain than getting electrocuted, though.