House Wiring
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From: Adam on 14 Oct 2007 19:52 Robert M. Riches Jr. wrote: >> your typical American house has two 110-120V feeds out of phase. [snip] >> Somehow the two feeds are combined to get 220-240V > > Right. The "somehow" is the feed coming into the house is > essentially 220V with a center tap. The two outer lines are > called L1 and L2. The center tap is called N, for neutral, > and it is grounded at building entrances. (That's where the > power lines enter the building, not at the doors.) L1 and > L2 have 220V between them. L* and N have 110V between them. > Safety ground is routed separately from N Thanks VERY much for a simple and clear explanation of something I didn't quite understand before. I now also understand the difference between "hot" and "neutral" and "ground". (For polarized plugs, the narrower one is "hot", correct? Seems like almost everything has polarized plugs these days, even things where I don't think it would matter like incandescent lamps.) When I walk around to the side of my apartment building, there are two banks of five electric meters each, and each bank has an uninsulated thick multistrand wire (looks like a guy wire only larger) running from the bank of meters to a grounding rod. Is that "neutral" or "ground"? BTW that is about 20 feet from where the telco's box is connected to their grounding rod. Unruh wrote: > If you look at your breaker box, each alternate breaker is a different > phase line. parts of your house is wired with three wire cable ( hot black, > hot red and neutral white) which connect to alternative breakers. Thanks, I didn't know that. That explains why the 220V circuits have two adjoining breakers, with the switches connected. > Actually it is not clear it is safer. The crucial issue is the amperage > going through the body with a critical zone. IIRC it's something like 60 mA across the heart that's fatal, regardless of voltage. Reminds me of an episode of "Mythbusters" (an American TV show that tests urban legends). They wanted to test the "well known fact" that if a plugged-in appliance falls into the bathtub while you're in it, you'll be electrocuted. Their conclusion was that newer appliances with GFIs (ground fault interruptors) would be safe, but a pre-GFI appliance would indeed be fatal. >> Technical and economic >> circumstances made Westinghouse's alternating current superior to >> Edison's direct current. > > The technical issue was the necessity of driving the long distance lines at > high voltage, or the losses were prohibitive. And converting DV voltage > levels is very difficult esp then. So it sounds like one of those relatively rare cases where one system actually won because of its technical superiority. It's nice to know that that actually happens once in a while. Adam
From: Unruh on 14 Oct 2007 22:34 Adam <look(a)bottom.for.address> writes: >Robert M. Riches Jr. wrote: >>> your typical American house has two 110-120V feeds out of phase. >[snip] >>> Somehow the two feeds are combined to get 220-240V >> >> Right. The "somehow" is the feed coming into the house is >> essentially 220V with a center tap. The two outer lines are >> called L1 and L2. The center tap is called N, for neutral, >> and it is grounded at building entrances. (That's where the >> power lines enter the building, not at the doors.) L1 and >> L2 have 220V between them. L* and N have 110V between them. >> Safety ground is routed separately from N >Thanks VERY much for a simple and clear explanation of something I >didn't quite understand before. I now also understand the difference >between "hot" and "neutral" and "ground". (For polarized plugs, the >narrower one is "hot", correct? Seems like almost everything has >polarized plugs these days, even things where I don't think it would >matter like incandescent lamps.) It matters very much for incandescent lamps-- not for the lamp which does not care but for you. The lamp is or ratehr should be wired up so that the broad metal screw in is connected to the neutral and only that little button at the end is connected to the hot wire. That way if you accidentally touch the screw in while screwing in a light bulb to a live lamp while standing on a wet basement floor, you do not get electocuted. In fact incandescent lamps are one of the things it matters most for. >When I walk around to the side of my apartment building, there are two >banks of five electric meters each, and each bank has an uninsulated >thick multistrand wire (looks like a guy wire only larger) running from >the bank of meters to a grounding rod. Is that "neutral" or "ground"? >BTW that is about 20 feet from where the telco's box is connected to >their grounding rod. Yes, that is the grounding rod. Neutral and ground are connected together in your breaker box. >Unruh wrote: >> If you look at your breaker box, each alternate breaker is a different >> phase line. parts of your house is wired with three wire cable ( hot >black, >> hot red and neutral white) which connect to alternative breakers. >Thanks, I didn't know that. That explains why the 220V circuits have >two adjoining breakers, with the switches connected. >> Actually it is not clear it is safer. The crucial issue is the amperage >> going through the body with a critical zone. >IIRC it's something like 60 mA across the heart that's fatal, regardless >of voltage. Reminds me of an episode of "Mythbusters" (an American TV >show that tests urban legends). They wanted to test the "well known >fact" that if a plugged-in appliance falls into the bathtub while you're >in it, you'll be electrocuted. Their conclusion was that newer >appliances with GFIs (ground fault interruptors) would be safe, but a >pre-GFI appliance would indeed be fatal. >>> Technical and economic >>> circumstances made Westinghouse's alternating current superior to >>> Edison's direct current. >> >> The technical issue was the necessity of driving the long distance >lines at >> high voltage, or the losses were prohibitive. And converting DV voltage >> levels is very difficult esp then. >So it sounds like one of those relatively rare cases where one system >actually won because of its technical superiority. It's nice to know >that that actually happens once in a while. >Adam
From: Robert M. Riches Jr. on 15 Oct 2007 13:51 On 2007-10-14, Adam <look(a)bottom.for.address> wrote: > Robert M. Riches Jr. wrote: >>> your typical American house has two 110-120V feeds out of phase. > [snip] >>> Somehow the two feeds are combined to get 220-240V >> >> Right. The "somehow" is the feed coming into the house is >> essentially 220V with a center tap. The two outer lines are >> called L1 and L2. The center tap is called N, for neutral, >> and it is grounded at building entrances. (That's where the >> power lines enter the building, not at the doors.) L1 and >> L2 have 220V between them. L* and N have 110V between them. >> Safety ground is routed separately from N > > Thanks VERY much for a simple and clear explanation of something I > didn't quite understand before. I now also understand the difference > between "hot" and "neutral" and "ground". (For polarized plugs, the > narrower one is "hot", correct? Seems like almost everything has > polarized plugs these days, even things where I don't think it would > matter like incandescent lamps.) There _are_ a lot of things that come with polarized plugs that really don't need them. However, there is _some_ justification for a lamp to be polarized. When you're putting a bulb into the socket, the threaded shell of the bulb can be touched by human fingers while it is in contact with the socket. If you're touching something grounded with one hand and the other hand makes contact with Hot/Line, you're going to know about it. If the outer shell is Neutral, you're not going to get nearly as big a shock. I learned that concept myself while a freshman in college. I had built a stereo amplifier with an aluminum chassis. I had the chassis grounded, because I had used CMOS inverters as analog amplifier elements, so I needed to protect the CMOS from static while soldering and such. I pulled out the cylindrical fuse while holding the chassis with the other hand. I had made the mistake of putting the hot wire from the line cord on the _outer_ connector on the fuse socket. When the fuse was almost out of the socket, my fingers contacted the outer end of the fuse at the same time as the inner end of the fuse contacted the outer terminal inside the socket. Remember, my other hand was holding the grounded chassis. YYYYYOOOOOWWWWW!!!!! The shock caused me to throw the fuse clear across the room, and it took a while to find it. Luckily, the fuse didn't break. > When I walk around to the side of my apartment building, there are two > banks of five electric meters each, and each bank has an uninsulated > thick multistrand wire (looks like a guy wire only larger) running from > the bank of meters to a grounding rod. Is that "neutral" or "ground"? > BTW that is about 20 feet from where the telco's box is connected to > their grounding rod. The big wire going to the ground rod would be considered Ground. In a panel that is considered an "entrance" panel, the ground and neutral are connected together inside the panel. In any subpanels, they are kept separate. -- Robert Riches spamtrap42(a)verizon.net (Yes, that is one of my email addresses.)
From: William Bagwell on 15 Oct 2007 20:12 On Mon, 15 Oct 2007 17:51:44 GMT, "Robert M. Riches Jr."> wrote: >snip >The big wire going to the ground rod would be considered >Ground. In a panel that is considered an "entrance" panel, >the ground and neutral are connected together inside the >panel. In any subpanels, they are kept separate. Yes, keeping them separate everywhere except the main panel is a (US) code requirement. When I built my house years ago, I put all the grounds on one side and all the neutrals on the other. Even though they are connected this allows the possibility to easily convert my main panel to a sub panel if the need ever arises. Simply remove the jumper bar and instant sub panel... -- William
From: Peter D. on 15 Oct 2007 20:55
on Tuesday 16 October 2007 03:51 in the Usenet newsgroup alt.os.linux.mandrake Robert M. Riches Jr. wrote: [snip] > There _are_ a lot of things that come with polarized plugs > that really don't need them. However, there is _some_ > justification for a lamp to be polarized. When you're > putting a bulb into the socket, the threaded shell of the > bulb can be touched by human fingers while it is in contact > with the socket. If you're touching something grounded with > one hand and the other hand makes contact with Hot/Line, > you're going to know about it. If the outer shell is > Neutral, you're not going to get nearly as big a shock. The Edison Screw light bulb is another black mark for American electricity. It is invading Australia. The bayonet socket has both contacts well hidden. Protecting against clumsy fingers and incompetent home handy-persons. > I learned that concept myself while a freshman in college. > I had built a stereo amplifier with an aluminum chassis. I > had the chassis grounded, because I had used CMOS inverters > as analog amplifier elements, so I needed to protect the > CMOS from static while soldering and such. I pulled out the > cylindrical fuse while holding the chassis with the other > hand. I had made the mistake of putting the hot wire from > the line cord on the _outer_ connector on the fuse socket. > When the fuse was almost out of the socket, my fingers > contacted the outer end of the fuse at the same time as the > inner end of the fuse contacted the outer terminal inside > the socket. Remember, my other hand was holding the > grounded chassis. YYYYYOOOOOWWWWW!!!!! The shock caused me > to throw the fuse clear across the room, and it took a while > to find it. Luckily, the fuse didn't break. Your biggest concern was the fuse? -- sig goes here... Peter D. |