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Old 2020-08-28, 20:11   #67
PhilF
 
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Quote:
Originally Posted by chalsall View Post
BUT, importantly... Ground should never actually carry any current. It's there as a safety feature
This is correct. Neutral also allows for easy distribution of both 240V( for high current appliances) and 120V (for the regular house outlets).

In most of the USA the outside pole transformer has a 240V secondary, center tapped. The center tap is connected to ground at the transformer and labeled neutral. This means one side of the transformer to neutral gives us 120V, while the other side of the transformer also gives us 120V (180 degrees out of phase). So it is easy to wire up half the 120V outlets from one "hot" to neutral and the other half of them to the other "hot" and neutral in order to spread the load across both halves of the transformer's secondary.

240V outlets are wired hot to hot; neutral is not used.

This leaves ground (earth) available for safety features, and as Chris said, should never carry any current.
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Old 2020-08-28, 21:20   #68
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And of course all this is remnant of Tesla's original idea to use Earth as one of the two conductors/poles of electricity. It is counteractive to consider Earth as a conductor but at high enough voltages and wide enough cross-area it does just that.

https://www.quora.com/Is-the-earth-a...fety%20purpose.

BTW Excellent/Expert posts by PhilF.
Not many know that The North-American Ovens/Ranges/Stoves run on 240 v., despite using them on a daily basis.

https://www.hunker.com/13414122/size...electric-stove

Last fiddled with by a1call on 2020-08-28 at 21:22
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Old 2020-08-28, 22:38   #69
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Quote:
Originally Posted by PhilF View Post
In most of the USA the outside pole transformer has a 240V secondary, center tapped. The center tap is connected to ground at the transformer and labeled neutral. This means one side of the transformer to neutral gives us 120V, while the other side of the transformer also gives us 120V (180 degrees out of phase). So it is easy to wire up half the 120V outlets from one "hot" to neutral and the other half of them to the other "hot" and neutral in order to spread the load across both halves of the transformer's secondary.

240V outlets are wired hot to hot; neutral is not used.
The beauty of AC: when you write '120V' you really mean 'Oscillating from +120V to -120V at 50 or 60Hz', so hooking up one hot wire to one such pulsating voltage (call it A) and another to a 180-degree-out-of-phase one (B) gives us 'Oscillating from +240V to -240V at 50 or 60Hz', since 'voltage' means 'potential difference', and calling A = sin(c*t) means the 180-degree-out-of-phase-signal B = -sin(c*t), thus V = A-B = 2*sin(c*t).
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Old 2020-08-28, 22:45   #70
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Quote:
Originally Posted by ewmayer View Post
The beauty of AC: when you write '120V' you really mean 'Oscillating from +120V to -120V ...
Almost. 120V (and 240V) are rms values. So the peak is higher than 120V.
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Old 2020-08-28, 22:46   #71
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Quote:
Originally Posted by ewmayer View Post
The beauty of AC: when you write '120V' you really mean 'Oscillating from +120V to -120V at 50 or 60Hz', so hooking up one hot wire to one such pulsating voltage (call it A) and another to a 180-degree-out-of-phase one (B) gives us 'Oscillating from +240V to -240V at 50 or 60Hz', since 'voltage' means 'potential difference', and calling A = sin(c*t) means the 180-degree-out-of-phase-signal B = -sin(c*t), thus V = A-B = 2*sin(c*t).
Couldn't have said it better myself!

Ok, I admit, I couldn't have said it at all. If I had the math skills of most of you guys I could have gone a lot further in life.
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Old 2020-08-28, 23:04   #72
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Quote:
Originally Posted by retina View Post
Almost. 120V (and 240V) are rms values. So the peak is higher than 120V.
I stand corrected - and note that I forgot to include the needed voltage multiplier in my trig terms anyway. So, let's do that: RMS means we need to integrate sin^2 over a full cycle and take the square root of the result: Using the identity sin^2(x) = [1-cos(2x)]/2 and integrating from 0 to 2*pi gives (the cos(2*x) term integrates to 0) result 2*pi/2 = pi, to get mean-square we divide by the length of the interval of integration, 2*pi, thus 1/2, RMS = square root of that, sqrt(1/2). Thus a nominal (RMS) voltage of 120 means a peak voltage 120*sqrt(2) ~= 170, and the corrected equation for the in-phase signal is A = 120*sqrt(2)*sin(c*t).

I shoulda been an electrificationistician, I tells ya. But such a second career would only tempt me if it came with the "plumber's privilege", by which I refer, of course, the undisputed freedom to squat down while working and wearing too-short jeans so as to reveal multiple inches of butt-crack. :)

Last fiddled with by ewmayer on 2020-08-28 at 23:08
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Old 2020-08-28, 23:14   #73
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Quote:
Originally Posted by ewmayer View Post
I stand corrected - and note that I forgot to include the needed voltage multiplier in my trig terms anyway. So, let's do that: RMS means we need to integrate sin^2 over a full cycle and take the square root of the result: Using the identity sin^2(x) = [1-cos(2x)]/2 and integrating from 0 to 2*pi gives (the cos(2*x) term integrates to 0) result 2*pi/2 = pi, to get mean-square we divide by the length of the interval of integration, 2*pi, thus 1/2, RMS = square root of that, sqrt(1/2). Thus a nominal (RMS) voltage of 120 means a peak voltage 120*sqrt(2) ~= 170, and the corrected equation for the in-phase signal is A = 120*sqrt(2)*sin(c*t).

I shoulda been an electrificationistician, I tells ya. But such a second career would only tempt me if it came with the "plumber's privilege", by which I refer, of course, the undisputed freedom to squat down while working and wearing too-short jeans so as to reveal multiple inches of butt-crack. :)
All of that is a (very) long way of saying that peak = rms * 1.41.

I shoulda been a mathistician, I tells ya! But such a second career would only tempt me if I were a glutton for punishment.

Last fiddled with by PhilF on 2020-08-28 at 23:28
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Old 2020-08-29, 00:42   #74
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Quote:
Originally Posted by ewmayer View Post
But such a second career would only tempt me if it came with the "plumber's privilege", by which I refer, of course, the undisputed freedom to squat down while working and wearing too-short jeans so as to reveal multiple inches of butt-crack. :)
A Cultural History of the Plumber’s Crack | MEL Magazine

I see that in the UK the "plumber's crack" go by the monicker "builder's bum".

And here is a link to the classic example of a handyman exercising the aforementioned privilege detailed in the first article, as portrayed by a young Dan Ackroyd in a classic glory-days-of-SNL sketch:

https://www.youtube.com/watch?v=SSe6yxKy4r8
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Old 2020-08-29, 02:06   #75
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Another counterintuitive and usually disputed fact (by masses/average-Joe) is that doubling the voltage (say that of the potential in a capacitor) will square the energy (stored in it).

https://www.quora.com/When-you-doubl...double-as-well
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Old 2020-08-29, 04:19   #76
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Quote:
Originally Posted by chalsall View Post
It carries the current from "Hot" back to the panel, after doing whatever work it is the device does.

It is very similar to Ground (AKA "Earth"), and in fact Neutral and Ground are tied together at the panel.

BUT, importantly... Ground should never actually carry any current. It's there as a safety feature (and some devices don't even use it). There's a reason bathroom outlets, for example, have Ground Fault Interrupters (GFI) which kill the Hot the instant any current is detected passing back through the Ground.
GFI compare the current in the L and N conductors, and trip if there is an imbalance (current leakage) that exceeds the design specification. Not necessary for there to be current on Ground.
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Old 2020-08-29, 05:34   #77
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Saturday morning rant...

L-L vs L-N: During the early electricity times (think Edison, Bell, telegraph), people found that Earth is a very good conductor for electricity. Therefore, they "saved" the costs on wires, by running only one wire from the transmitter to the receiver, and connecting the other to the earth (or, in case of telegraph, which used to run along the railways for trains, connecting it to the iron rails, Edison had a "patent" for this idea, haha). So, the electrons come to you through a wire, and return back to the source through the soil or train rails. Or viceversa. On the way, they do some work, like toasting your bread or washing your clothes, or finding prime numbers in your computer (the scientists could not agree yet why computers should contain any prime number, but they do, sometimes).

Later, when the AC slowly substituted the DC, the "habit" remained, between transformers, you connect one wire to the earth, and only one wire runs on the pylons (or towers). You have to dig a hole on each side of the circuit and put a large metal plate inside (to cover for the amount of current, these are big copper blocks with quite a large surface area, many square meters). This is massive, yet much cheaper than running one more copper wire from one place to the other (think about how much volume of copper you have in a half inch thick cable running for few tens of kilometers, how heavy that is, therefore how much additional steel cable you need to sustain it, etc, big pain in the butt). Now, the things are trickier, due to the nature of the AC current, and all the transformers in the middle (that is why AC was adopted, because it is/was at the time, infinitely easier to "transform" from high current to high voltage, to minimize the losses on wires, then back from high voltage to high current in your house, to maximize the efficiency of your toaster and reduce the risk of you being electrocuted). In the beginning, there was no "neutral" for AC, and all the wires run through the.. wire. Some countries which still live in the past ( ) and dream of their former glory when they were an empire and ruled the earth, still keep this nomination, with L1 and L2. But that is not anymore true. Think about connecting all transformers in the middle to the earth on both sides, they didn't really know how to do it. This would not really work (why?). So, you technically got two "hots" in your house, you could get shocks by touching any of them (because somewhere on the way, there is a transformer which is connected to the ground, and the circuit closes through you). Later, people found ways to always connect one of the wires to the ground, even for the wires coming to your house, after the last transformer, and that wire is the "neutral". It means, it saves copper, and you don't get electric shocks if you touch it. But it is not "safer". It just saves copper. If no wire would be connected to earth EVER (not at your house, not at the power plant, no on the way) then the only way for you to get electric shock would be to touch both of the wires in the same time. I mean, probabilistic, this is less probable than in actual situation, when you can get electric shock by touching only one wire, the hot wire (the one not connected to ground) if you are not insulated from ground. And the reason is exactly that: somewhere on the way between power plant and you, there is a wire connected to the ground, through which you close the circuit with your body. That's the "neutral". If you have insulated shoes, rubber sleepers, whatever, you won't get electric shock, even if you touch the line. That's why birds sitting a the wires wont get electrocuted unless they touch the pylons too, etc. They don't "close the circuit" to the earth.

Moral: You get electric shock for only two reasons:

1. somebody wanted to save money on copper
2. you were stupid and touched the wire

The "earth" or "ground" wire (the third one in the socket) has nothing to do with electricity transport, it is there just for safety, in case a short circuit happens in your toaster, between the hot (line) and some metal part of the device, then the electricity would leak to the ground through this third wire, and won't shock you much (pun intended) when you take the toast out of the machine. From the electric point of view, the neutral and the earth/ground wires are connected to the same point at the provider side (earth), and are connected to different points on your side, the neutral goes to the circuit, the ground goes to the chassis of the toaster. If you switch them, it would still work the same, except the connection on the other side may not be good enough to cover for the amperage.

I remember in communist Romania of the 70s and 80s, people use to "steal" electricity from "the company". All meters were installed on the line (normal/correct procedure) but people used to dig a hole in the wall and switch the wires in the wall, also switch the earth and neutral. This was possible, because the earths were connected to the centralized heaters, a big mass of iron running all around the city, connected to the ground everywhere (the pipes were buried in the ground, etc). This way, the meter would be connected on the neutral, but this would not be visible from outside, the wires at the panel would look the same, and would still record corectly as long as somebody from the company would come to check it, but when you had large consumers, like a 4kW heater in the winter when there are -30°C outside, and you get "centralized heat" from the city only 2-3 hours per day, and you have a baby in your house who won't like much the 13°C in the room, you would switch the "neutrals" so the electricity comes on the "line" and goes back to the company on the "earth" (skipping the counter, which is on the "neutral") and everything was fine

Last fiddled with by LaurV on 2020-08-29 at 05:51
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