I’ve long ago made my peace with polarized plugs (Cecil’s post on this, [URL=“I can’t plug in these new plugs! What’s the deal? - The Straight Dope”]) is pretty dated, from 1983, but for all I’ve read explaining them, Cecil’s included, I’m still confused. Yes, I understand that only one plug is “hot,” but we’re talking about alternating current. Since the current changes direction 60 times a second, why isn’t each plug (and wire) “hot” thirty times a second?
Here’s the link to the column: I can’t plug in these new plugs! What’s the deal? - The Straight Dope
The polarity is irrelevant. One side of the plug is connected to ground and one is “live”. If you touch the grounded one, nothing happens. If you touch the live one, you become part of the connection to ground and the circuit is completed through you. The fact that the electrons “change direction” 60 times a second (or 50 if you on on the other side of the pond) makes no difference to the fact that they are flitting back and forth through you.
The hot side switches from +120 to -120, while the neutral side stays at zero. Both sides carry essentially the same current, it’s the voltage which makes one side hot.
That would give you somewhere around 240 volts (I say “somewhere” because I’m not sure how root-mean-square voltage figures into that, if it figures into it at all). If there is no circuit path the neutral side carries no voltage or current - there is no place for it to get the current from (even if current without voltage makes sense). You simply can’t make a circuit to ground if you grab the neutral, and that’s exactly what you do if you grab the hot side.
It’s 120 above 0 and then 120 below zero and that is the root-mean-square value. On one alternation the voltage goes to about 170 or so volts (it varies from place to place). The neutral stays at zero as long as it stays connected to the center-tap of the transformer and the center tap of the transformer stays grounded. The voltage of the hot conductor changes relative to that reference point.
The thing that stood out most to me about this article was that the H1N1 vaccine was apparently created a long time ago. But my question is, how did they work before? Was one of the prongs still ground, but they didn’t specify which? Or were the outlets themselves much more unsafe? And how do three-prong plugs fit in? I was always taught that the third prong was ground.
If I understand it correctly, on a polarized or unpolarized plug, one is neutral and supposed to be grounded; the polarized plug merely establishes which is which. On a three-prong plug, the third prong is guaranteed to be grounded, which takes a bit of extra work if the in-wall wiring wasn’t built with a third wire in the first place.
All three are safe if everything is working right. But polarized plugs are safer when something goes wrong, and grounded plugs are even safer.
The current that goes into your home is 240/220 volts. What happens is that your outlets are attached to one side of this loop (with the current going +120/110 to -120/110) and a neutral ground wire. Since the ground always has zero volts going through it, the difference between that and one hot lead is 120/110 volts.
And, it is still AC voltage since the current goes in the direction of the voltage.
The 120/110 voltage is standard for North America. The rest of the world keeps their power at 240/220 volts.
See this Straight Dope Column: How Come the U.S. Uses 120 Volt Electricity and not 240 Like the Rest of the World?
a non-polarized or non-grounded plug can be hazardous even when working right.
a metal chassis of an electrical device could be connected unswitched to one prong of the plug. if the plug was connected so that that prong would be hot then the chassis of the device would be electrified and could result in a shock if touched.
Granted, but I’m pretty sure the chassis is supposed to be insulated from both sides; I’ve dissected enough all-but-antique appliances to know that they’re built that way. The Devil is in that “supposed to be” – a fairly mild mechanical derangement and – ZZZAP!!
some chassis did have only a fairly weak pressed board backing or barrier, these sooner or later broke and were left off, heads of mounting screws could be hot even if in place.
control knob metal shafts could be hot and the wood or plastic knob no longer be in place.
it is correct that there were non-durable or easily circumvented (hot contact could still be made with the protections in place with fingers or objects) protections.
If polarized plugs (we call them bigfoot-littlefoot in my family) are safer than non-polarized, why do so many electric devices still have the non-polarized ones?
Those are double insulated. They have multiple layers of insulation preventing exposure to live voltage.
Perhaps they have no exposed metal parts that could conduct current to ground.