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Posted: 5/20/2021 9:24:12 PM EDT
[#1]
Quote HistoryQuoted: Still getting the differential answer as it’s the way we measure it. I did not ask what the voltage differential from ground and neutral is. Voltage is “pressure” to drive current. Neutral is a path back to the transformer is another thing I keep hearing that makes no sense. Its alternating current not direct. That makes zero sense. If the voltage and current changes direction 120 times a second from -170volts (or so for 240v split) to +170volts. How the hell is neutral not carrying the exact same voltage as line? That’s where I get lost. If you don’t agree that peak voltage is 160-170volts you may not want to chime in. Another that confuses me... if a circuit has a light bulb that draws 10 amps (big light bulb). If we measure current, which we can do. Neutral and line will both measure 10amps...ohms law saws? I’m not in question of what we can and can not measure. I’m questioning what’s really there that we can not. Maybe it can be measured with a scope? Not an EE or in the field, but I just treat neutral/white as carrying current too and it measures carrying current. The third bare/green AFAIK is just a local earth ground that's really only there to give lightning strikes a more attractive path to ground than your equipment, and not really anything else (I gather the local earth ground won't reliably flip a breaker). |
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Posted: 5/20/2021 9:25:23 PM EDT
[#2]
Quote HistoryQuoted: Still getting the differential answer as it’s the way we measure it. I did not ask what the voltage differential from ground and neutral is. Voltage is “pressure” to drive current. Neutral is a path back to the transformer is another thing I keep hearing that makes no sense. Its alternating current not direct. That makes zero sense. If the voltage and current changes direction 120 times a second from -170volts (or so for 240v split) to +170volts. How the hell is neutral not carrying the exact same voltage as line? That’s where I get lost. If you don’t agree that peak voltage is 160-170volts you may not want to chime in. Another that confuses me... if a circuit has a light bulb that draws 10 amps (big light bulb). If we measure current, which we can do. Neutral and line will both measure 10amps...ohms law saws? I’m not in question of what we can and can not measure. I’m questioning what’s really there that we can not. Maybe it can be measured with a scope? Peak Peak to peak Average RMS all the things... |
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Posted: 5/20/2021 9:27:09 PM EDT
[#3]
Quote HistoryQuoted: This sounds like #fakenews. Not fake at all. A single XYZv CT stepdown xfrmer has in it only a single magnetic field (it's fed from only 1ph, A B or C, of a 3ph feeder), hence it can only be a single phase. The "poles" in a CT panel is not 2ph. 
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Posted: 5/20/2021 9:30:17 PM EDT
[#4]
Quote HistoryQuoted: Voltage is a measurement of potential difference. Well, sort of, but trying to explain it w/o using the terms is hard. Neutral bonds to earth. So voltage (potential) difference is squat. If you measure neutral to ground, you get squat. If you measure hot to the same hot leg, you get squat. There is no DIFFERENCE. If you measure in your box L1 to neutral, you get 120v. If you measure in your box L2 to neutral, you get 120v. If you measure L1 to L2, you get 240. Wait, what? Each leg is only 120v to neutral, but they are 240 when measuring the difference between them because they are in opposite phase. L1 is -120v when L2 is +120v, etc. That is why you can power your entire panel with a 120v generator, just not run any 240v appliances. 240v appliances also don't need a neutral (unless they use L1 to power a 120v internal widget), as in the case of a 240v heater. I've installed many. You have 3 wires to the heater: L1, L2, Ground. No neutral needed. But how is this? You are measuring differences, and there is a potential difference of 240v between L1 an L2, so you don't need another conductor to have a difference to. Clear as mud? I think what he is trying to ask is if the the two legs that are out of phase with one another cancel out (on the neutral) because it is common to both lines. |
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Posted: 5/20/2021 9:30:55 PM EDT
[#5]
Quote HistoryQuoted: Huh. If it’s that easy to generate high voltage, why do power companies spend millions on generators and GSUs? Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. |
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Posted: 5/20/2021 9:33:27 PM EDT
[#6]
Quote HistoryQuoted: Opposite phase? So the power company brings in 2 phases? Neat! #learningnewthings No they don't they provide 1 phase that is split |
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Posted: 5/20/2021 9:35:43 PM EDT
[#7]
Quote HistoryQuoted: Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. Quote HistoryQuoted: Quoted: Huh. If it’s that easy to generate high voltage, why do power companies spend millions on generators and GSUs? Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. Oh that makes perfect sense. #knowledge How do they add or remove electrons from the line? Van De Graff generators? |
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Posted: 5/20/2021 9:37:15 PM EDT
[#8]
Quote HistoryQuoted: Oh that makes perfect sense. #knowledge How do they add or remove electrons from the line? Van De Graff generators? Magnets. |
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Posted: 5/20/2021 9:38:43 PM EDT
[#9]
Quote HistoryQuoted: Magnets. Quote HistoryQuoted: Quoted: Oh that makes perfect sense. #knowledge How do they add or remove electrons from the line? Van De Graff generators? Magnets. That’s a lie. |
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Posted: 5/20/2021 9:40:06 PM EDT
[#10]
Quote HistoryQuoted: Not an EE or in the field, but I just treat neutral/white as carrying current too and it measures carrying current. The third bare/green AFAIK is just a local earth ground that's really only there to give lightning strikes a more attractive path to ground than your equipment, and not really anything else (I gather the local earth ground won't reliably flip a breaker). Prem wiring has 100% nothing to do with lightning. NFPA has a separate codebook for lighting arrest systems. A green insulated wire serves same purpose as the bare wire, fault clearing, aka "EGC". Insulated EGC's are insulated only when called for as described by the NEC codebook, like to pools/spas, in conduit as individual wires, etc. A lightning strike to your house will use bare and N wires equally, they are both bonded together in the service panel and then a 'fat' bare tied to a healthy ground rod or other Earth ground. |
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Posted: 5/20/2021 9:41:41 PM EDT
[#11]
Quote HistoryQuoted: Well, technically, there is absolute, because when you whittle it down, it's all about joules. A plate of charge, like in a capacitor, when you do work (expend energy) to push electrons to one side, 1J per 1C of electrons = 1v. In this example the cap holds potential energy in the electrons of 1J (1C x 1v). v=J/C. So technically there is absolute voltage, and you can read this using a V meter that has infinite ohms when you attach the probes. You only get amps when the differential is connected (ckt completed) so the electrons that have potential energy can rush-a-homa. There is no such thing as absolute voltage measured at a single point. That defies the very definition of voltage, which is the potential energy created when you move a unit of charge (free electrons) a given distance. Distance > 2 points. |
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Posted: 5/20/2021 9:44:43 PM EDT
[#12]
Quote HistoryQuoted: Not an EE or in the field, but I just treat neutral/white as carrying current too and it measures carrying current. The third bare/green AFAIK is just a local earth ground that's really only there to give lightning strikes a more attractive path to ground than your equipment, and not really anything else (I gather the local earth ground won't reliably flip a breaker). Quote HistoryQuoted: Quoted: Still getting the differential answer as it’s the way we measure it. I did not ask what the voltage differential from ground and neutral is. Voltage is “pressure” to drive current. Neutral is a path back to the transformer is another thing I keep hearing that makes no sense. Its alternating current not direct. That makes zero sense. If the voltage and current changes direction 120 times a second from -170volts (or so for 240v split) to +170volts. How the hell is neutral not carrying the exact same voltage as line? That’s where I get lost. If you don’t agree that peak voltage is 160-170volts you may not want to chime in. Another that confuses me... if a circuit has a light bulb that draws 10 amps (big light bulb). If we measure current, which we can do. Neutral and line will both measure 10amps...ohms law saws? I’m not in question of what we can and can not measure. I’m questioning what’s really there that we can not. Maybe it can be measured with a scope? Not an EE or in the field, but I just treat neutral/white as carrying current too and it measures carrying current. The third bare/green AFAIK is just a local earth ground that's really only there to give lightning strikes a more attractive path to ground than your equipment, and not really anything else (I gather the local earth ground won't reliably flip a breaker). Grounds are just for lightning protection? Interesting... #cometoGDlearn |
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Posted: 5/20/2021 9:45:14 PM EDT
[#13]
Quote HistoryQuoted: Peak Peak to peak Average RMS all the things... Quote HistoryQuoted: Quoted: Still getting the differential answer as it’s the way we measure it. I did not ask what the voltage differential from ground and neutral is. Voltage is “pressure” to drive current. Neutral is a path back to the transformer is another thing I keep hearing that makes no sense. Its alternating current not direct. That makes zero sense. If the voltage and current changes direction 120 times a second from -170volts (or so for 240v split) to +170volts. How the hell is neutral not carrying the exact same voltage as line? That’s where I get lost. If you don’t agree that peak voltage is 160-170volts you may not want to chime in. Another that confuses me... if a circuit has a light bulb that draws 10 amps (big light bulb). If we measure current, which we can do. Neutral and line will both measure 10amps...ohms law saws? I’m not in question of what we can and can not measure. I’m questioning what’s really there that we can not. Maybe it can be measured with a scope? Peak Peak to peak Average RMS all the things... Whoa! That’s sounds sciency! |
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Posted: 5/20/2021 9:46:14 PM EDT
[#14]
Quote HistoryQuoted: I think what he is trying to ask is if the the two legs that are out of phase with one another cancel out (on the neutral) because it is common to both lines. Quote HistoryQuoted: Quoted: Voltage is a measurement of potential difference. Well, sort of, but trying to explain it w/o using the terms is hard. Neutral bonds to earth. So voltage (potential) difference is squat. If you measure neutral to ground, you get squat. If you measure hot to the same hot leg, you get squat. There is no DIFFERENCE. If you measure in your box L1 to neutral, you get 120v. If you measure in your box L2 to neutral, you get 120v. If you measure L1 to L2, you get 240. Wait, what? Each leg is only 120v to neutral, but they are 240 when measuring the difference between them because they are in opposite phase. L1 is -120v when L2 is +120v, etc. That is why you can power your entire panel with a 120v generator, just not run any 240v appliances. 240v appliances also don't need a neutral (unless they use L1 to power a 120v internal widget), as in the case of a 240v heater. I've installed many. You have 3 wires to the heater: L1, L2, Ground. No neutral needed. But how is this? You are measuring differences, and there is a potential difference of 240v between L1 an L2, so you don't need another conductor to have a difference to. Clear as mud? I think what he is trying to ask is if the the two legs that are out of phase with one another cancel out (on the neutral) because it is common to both lines. You don't cancel out voltage, it is there or it isn't. It is only a question of what and how you measure. |
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Posted: 5/20/2021 9:46:37 PM EDT
[#15]
Quote HistoryQuoted: Prem wiring has 100% nothing to do with lightning. NFPA has a separate codebook for lighting arrest systems. A green insulated wire serves same purpose as the bare wire, fault clearing, aka "EGC". Insulated EGC's are insulated only when called for as described by the NEC codebook, like to pools/spas, in conduit as individual wires, etc. A lightning strike to your house will use bare and N wires equally, they are both bonded together in the service panel and then a 'fat' bare tied to a healthy ground rod or other Earth ground. Quote HistoryQuoted: Quoted: Not an EE or in the field, but I just treat neutral/white as carrying current too and it measures carrying current. The third bare/green AFAIK is just a local earth ground that's really only there to give lightning strikes a more attractive path to ground than your equipment, and not really anything else (I gather the local earth ground won't reliably flip a breaker). Prem wiring has 100% nothing to do with lightning. NFPA has a separate codebook for lighting arrest systems. A green insulated wire serves same purpose as the bare wire, fault clearing, aka "EGC". Insulated EGC's are insulated only when called for as described by the NEC codebook, like to pools/spas, in conduit as individual wires, etc. A lightning strike to your house will use bare and N wires equally, they are both bonded together in the service panel and then a 'fat' bare tied to a healthy ground rod or other Earth ground. Fault clearing? That’s why I have a lawyer. It’s the electricians fault for sure! |
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Posted: 5/20/2021 9:48:31 PM EDT
[#16]
Quote HistoryQuoted: Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. You serious Clark? Power companies do not form electrons. Do you seriously think that they are creating matter? |
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Posted: 5/20/2021 9:51:19 PM EDT
[#17]
Quote HistoryQuoted: You serious Clark? Power companies do not form electrons. Do you seriously think that they are creating matter? Quote HistoryQuoted: Quoted: Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. You serious Clark? Power companies do not form electrons. Do you seriously think that they are creating matter? The very definition of a generator means it generates electrons. It adds electrons to the wire. |
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Posted: 5/20/2021 9:51:52 PM EDT
[#18]
Quote HistoryQuoted: Grounds are just for lightning protection? Interesting... #cometoGDlearn Also completely wrong, but whatever. |
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Posted: 5/20/2021 9:52:25 PM EDT
[#19]
Quote HistoryQuoted: You serious Clark? Power companies do not form electrons. Do you seriously think that they are creating matter? Quote HistoryQuoted: Quoted: Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. You serious Clark? Power companies do not form electrons. Do you seriously think that they are creating matter? Of course not. They just move electrons from one phase to another phase to produce the proper voltage differentials between the phases. (Or source and sink them from the neutral connection if the 3 phase generator has a neutral connection) |
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Posted: 5/20/2021 9:52:53 PM EDT
[#20]
Quote HistoryQuoted: Also completely wrong, but whatever. Quote HistoryQuoted: Quoted: Grounds are just for lightning protection? Interesting... #cometoGDlearn Also completely wrong, but whatever. Science has no place here. Just go with the flow. |
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Posted: 5/20/2021 9:53:19 PM EDT
[#21]
Quote HistoryQuoted: I think what he is trying to ask is if the the two legs that are out of phase with one another cancel out because they share a common neutral. The poles in a panel are not out-of-phase, it's all the same phase, but while one side goes + the other side goes - There's only 1ph in a resi single family dwelling. The CT in a xfrmer does not magically create a new phase. In a 2ckt MWBC with one shared N wire, when both loads are 'on' at the same time and balanced, there's no current in the N wire. There is no cancelling of anything. Two 120v loads are in series at that point, hence it becomes a 240v load. There are cautions to be had with a MWBC. You can illustrate the amps of each 120v load in a MWBC (hot leg to N) and you'll see two current paths, one into the N wire and one out of the N wire, which then appears they cancel, which of course they do when the loads are equal, aka "balanced MWBC". Unbalanced load means some amps will still be on the N, but the N amps will never exceed a single load when loads are functioning normally. |
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Posted: 5/20/2021 9:55:36 PM EDT
[#22]
Quote HistoryQuoted: The very definition of a generator means it generates electrons. It adds electrons to the wire. No. It generates voltage (potential difference) through the input of a different type of work (mechanical rotational). The existing electrons then flow through the wires in an attempt to neutralize the generated potential difference, doing work in the process. |
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Posted: 5/20/2021 9:59:35 PM EDT
[#23]
Quote HistoryQuoted: There is no such thing as absolute voltage measured at a single point. That defies the very definition of voltage, which is the potential energy created when you move a unit of charge (free electrons) a given distance. Distance > 2 points. I don't need a differential to say what the volts are on a charged plate. I only need to know the joules and amount of charge. V=J/C Choosing a point to be the differential point is arbitrary. I have one plate that is 100v and then I arbitrarily choose another plate of 40v, the diff is 60v, but I don't need to choose an arbitrary point of reference to know what my initial plate voltage is. |
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Posted: 5/20/2021 10:02:54 PM EDT
[#24]
Quote HistoryQuoted: The very definition of a generator means it generates electrons. It adds electrons to the wire. Adding electrons must be a Elon Musk thing, he figured it out.  What if too many electrons are added, it pops like a cork? |
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Posted: 5/20/2021 10:04:03 PM EDT
[#25]
Quote HistoryQuoted: The poles in a panel are not out-of-phase, it's all the same phase, but while one side goes + the other side goes - There's only 1ph in a resi single family dwelling. The CT in a xfrmer does not magically create a new phase. In a 2ckt MWBC with one shared N wire, when both loads are 'on' at the same time and balanced, there's no current in the N wire. There is no cancelling of anything. Two 120v loads are in series at that point, hence it becomes a 240v load. There are cautions to be had with a MWBC. You can illustrate the amps of each 120v load in a MWBC (hot leg to N) and you'll see two current paths, one into the N wire and one out of the N wire, which then appears they cancel, which of course they do when the loads are equal, aka "balanced MWBC". Unbalanced load means some amps will still be on the N, but the N amps will never exceed a single load when loads are functioning normally. Pretty sure that is the answer OP is looking for - my question would be: what does the waveform of one leg look like on an oscilloscope? |
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Posted: 5/20/2021 10:04:20 PM EDT
[#26]
Quote HistoryQuoted: Also completely wrong, but whatever. Quote HistoryQuoted: Quoted: Grounds are just for lightning protection? Interesting... #cometoGDlearn Also completely wrong, but whatever. I think frayedknot was saying the same thing as you when used "interesting..." |
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Posted: 5/20/2021 10:07:43 PM EDT
[#27]
Quote HistoryQuoted: The very definition of a generator means it generates electrons. It adds electrons to the wire. Quote HistoryQuoted: Quoted: Quoted: Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. You serious Clark? Power companies do not form electrons. Do you seriously think that they are creating matter? The very definition of a generator means it generates electrons. It adds electrons to the wire.  ...
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Posted: 5/20/2021 10:12:58 PM EDT
[#28]
Quote HistoryQuoted: Of course not. They just move electrons from one phase to another phase to produce the proper voltage differentials between the phases. (Or source and sink them from the neutral connection if the 3 phase generator has a neutral connection) Quote HistoryQuoted: Quoted: Quoted: Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. You serious Clark? Power companies do not form electrons. Do you seriously think that they are creating matter? Of course not. They just move electrons from one phase to another phase to produce the proper voltage differentials between the phases. (Or source and sink them from the neutral connection if the 3 phase generator has a neutral connection) Oh this makes perfect sense. Thanks. |
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Posted: 5/20/2021 10:13:31 PM EDT
[#29]
Quote HistoryQuoted: Pretty sure that is the answer OP is looking for - my question would be: what does the waveform of one leg look like on an oscilloscope? The waveform of what? Volts? Looks 100% normal. Two loads (two 120v loads in series, balanced load or not) forms a CT with the ends hanging across the 240v in the panel. The CT is the N wire, aka zero volts or "grounded" line. |
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Posted: 5/20/2021 10:14:04 PM EDT
[#30]
Quote HistoryQuoted: I don't need a differential to say what the volts are on a charged plate. I only need to know the joules and amount of charge. V=J/C Choosing a point to be the differential point is arbitrary. I have one plate that is 100v and then I arbitrarily choose another plate of 40v, the diff is 60v, but I don't need to choose an arbitrary point of reference to know what my initial plate voltage is. I cannot help you if you fundamentally don't understand the definition of voltage. A Joule is a unit of work. Work = force * distance, hence again, 2 points. Voltage = force * distance per charge. How much work did I store up by moving a charge from point A to point B. Assuming you could manipulate individual electrons with your bare hands, to generate a voltage, you would have to pick up a free electron, and move it from one piece of material to another, sufficiently isolated from the first such that it couldn't return. The voltage would then be developed between the two objects between which you transferred the electron. Source: Master's Degree in Electromagnetics and employed in the power industry for 10 years. |
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Posted: 5/20/2021 10:14:17 PM EDT
[#31]
Quote HistoryQuoted: Adding electrons must be a Elon Musk thing, he figured it out. What if too many electrons are added, it pops like a cork? Quote HistoryQuoted: Quoted: The very definition of a generator means it generates electrons. It adds electrons to the wire. Adding electrons must be a Elon Musk thing, he figured it out. What if too many electrons are added, it pops like a cork? Kinda. Wire or equipment (whatever the limiting element is) becomes a fused disconnect. And you let the smoke out. |
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Posted: 5/20/2021 10:15:28 PM EDT
[#32]
Quote HistoryQuote HistoryQuoted: Quoted: Quoted: Quoted: Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. You serious Clark? Power companies do not form electrons. Do you seriously think that they are creating matter? The very definition of a generator means it generates electrons. It adds electrons to the wire. /media/mediaFiles/sharedAlbum/bubbles_zps5bf5952f_GIF-110.gif... Hey this is science. I’ll bet you don’t wear a mask. |
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Posted: 5/20/2021 10:16:05 PM EDT
[#33]
Quote HistoryQuoted: I think frayedknot was saying the same thing as you when used "interesting..." Quote HistoryQuoted: Quoted: Quoted: Grounds are just for lightning protection? Interesting... #cometoGDlearn Also completely wrong, but whatever. I think frayedknot was saying the same thing as you when used "interesting..." Do not sully my name! |
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Posted: 5/20/2021 10:18:08 PM EDT
[#34]
Quote HistoryQuoted: Pretty sure that is the answer OP is looking for - my question would be: what does the waveform of one leg look like on an oscilloscope? In homes (US, maybe elsewhere?) power is supplied by a center-tapped transformer on the pole, which comes into the house. The center tap is "neutral", the other two legs are L1 and L2. Between L1 and Neutral and L2 and Neutral are 120V of potential difference. Between L1 and L2 there is 240V of potential difference, because their AC sine waves are 180 degrees out of phase from each other. (The sine wave of one is at absolute positive when the sine wave of the other is absolute negative) Neutral is bonded to ground at the entrance... if you measure from neutral to ground you should read 0V In commercial or 3-phase applications, 3 phases are supplied that are actually 120degrees out of phase from each other. (Generators make power by making 360 degree rotations..e.g. a full rotation.) In these installations each phase to neutral is 120V of potential difference... but between any leg, is only about 208V, since they are only 120degrees out of phase. Voltage is by-definition the potential difference between two points... you have to accept that with voltage you are always measuring the DELTA between two points. |
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Posted: 5/20/2021 10:23:53 PM EDT
[#35]
Quote HistoryQuoted: Do not sully my name! Sorry. The stupid in this thread temporarily broke my sarcasm meter. |
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Posted: 5/20/2021 10:35:14 PM EDT
[#36]
Quote HistoryQuoted: Grounds are just for lightning protection? Interesting... #cometoGDlearn Quote HistoryQuoted: Quoted: Quoted: Still getting the differential answer as it’s the way we measure it. I did not ask what the voltage differential from ground and neutral is. Voltage is “pressure” to drive current. Neutral is a path back to the transformer is another thing I keep hearing that makes no sense. Its alternating current not direct. That makes zero sense. If the voltage and current changes direction 120 times a second from -170volts (or so for 240v split) to +170volts. How the hell is neutral not carrying the exact same voltage as line? That’s where I get lost. If you don’t agree that peak voltage is 160-170volts you may not want to chime in. Another that confuses me... if a circuit has a light bulb that draws 10 amps (big light bulb). If we measure current, which we can do. Neutral and line will both measure 10amps...ohms law saws? I’m not in question of what we can and can not measure. I’m questioning what’s really there that we can not. Maybe it can be measured with a scope? Not an EE or in the field, but I just treat neutral/white as carrying current too and it measures carrying current. The third bare/green AFAIK is just a local earth ground that's really only there to give lightning strikes a more attractive path to ground than your equipment, and not really anything else (I gather the local earth ground won't reliably flip a breaker). Grounds are just for lightning protection? Interesting... #cometoGDlearn And apparently they can be pretty complex to setup right ... something about where you put in the ground rods, etc. Of all the places to run into that, I learned it when reading about how to get 60hz mains hum out of audio recording/playback/equipment. ETA; Here, if you want to go down the rabbit hole: http://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf 1.2 - PROTECTION FROM LIGHTNING An EARTH ground is one actually connected to the earth and is necessary for LIGHTNING protection. Overhead power lines are frequent targets of lightning. Before modern standards such as the Code existed, power lines effectively directed lightning strikes into buildings, starting fires and killing people. Therefore, virtually all modern electric power is distributed over lines that have one conductor connected to earth ground periodically along its length. These and the earth ground at the service entry panel serve as easy, low-impedance paths to discharge lightning strikes before they can enter the building. Telephone, CATV, and satellite TV cables are also required to “arrest” lightning energy before it enters a building. Another benefit of the safety ground to earth ground connection is that, during an equipment fault event, only a few volts will be present on the exposed parts of the faulty device with respect to other earth-grounded objects. Since soil has resistance just like any other conductor, earth ground connections are not at zero volts, with respect to each other or any other mystical or “absolute” reference point. Code allows the resistance to earth (measured with special techniques) of a residential ground rod to be as high as 25 Ù. It is far too high to trip the circuit breaker under fault conditions in the dangerous hookup shown on the next page (claimed to be a “quieter” equipment ground). The soil resistance between separate ground rods can also allow thousands of volts to develop between them if lightning strike current should actually flow in one of them. This can seriously damage a computer modem, for example, if it “straddles” a computer (grounded via its power cord to the utility ground rod) and a telephone line protected via a separate ground rod. [3] For this reason, other protective ground connections (telephone, CATV, etc.) should be made to the same rod used for utility power, if at all possible. If multiple ground rods are used, Code requires that they all must be bonded to the main utility power grounding electrode. [4] From above PDF link. |
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Posted: 5/20/2021 10:36:08 PM EDT
[#37]
Quote HistoryQuoted: Pretty sure that is the answer OP is looking for - my question would be: what does the waveform of one leg look like on an oscilloscope? Quote HistoryQuoted: Quoted: The poles in a panel are not out-of-phase, it's all the same phase, but while one side goes + the other side goes - There's only 1ph in a resi single family dwelling. The CT in a xfrmer does not magically create a new phase. In a 2ckt MWBC with one shared N wire, when both loads are 'on' at the same time and balanced, there's no current in the N wire. There is no cancelling of anything. Two 120v loads are in series at that point, hence it becomes a 240v load. There are cautions to be had with a MWBC. You can illustrate the amps of each 120v load in a MWBC (hot leg to N) and you'll see two current paths, one into the N wire and one out of the N wire, which then appears they cancel, which of course they do when the loads are equal, aka "balanced MWBC". Unbalanced load means some amps will still be on the N, but the N amps will never exceed a single load when loads are functioning normally. Pretty sure that is the answer OP is looking for - my question would be: what does the waveform of one leg look like on an oscilloscope? Looks like this. This is one leg measured against the center tap....  Here are both legs measured against the center tap. Note they are of different polarization (180 degrees out of phase with relation to neutral)  ETA, here is what both legs would look like together leg to leg, no neutral (looks same as one leg to neutral) only difference would be a higher amplitude than just on leg to neutral, because the voltage is double..... ETA again, finally got the pics right, lol |
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Posted: 5/20/2021 10:38:50 PM EDT
[#38]
Quote HistoryQuoted: Hey this is science. I’ll bet you don’t wear a mask. Quote HistoryQuoted: Quoted: Quoted: Quoted: Quoted: Because they have customers who are using the voltage potential between the power lines and/or neutral to do work, letting electrons from between them. They have to make up the load the customers use by adding or removing more electrons to the lines to keep the voltage correct. You serious Clark? Power companies do not form electrons. Do you seriously think that they are creating matter? The very definition of a generator means it generates electrons. It adds electrons to the wire. /media/mediaFiles/sharedAlbum/bubbles_zps5bf5952f_GIF-110.gif... Hey this is science. I’ll bet you don’t wear a mask. This is science? lol... |
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Posted: 5/20/2021 10:41:17 PM EDT
[#39]
Quote HistoryQuoted: Looks like this. This is one leg measured against the center tap.... https://i.ibb.co/DM8vncq/20201218-165623.jpg Here are both legs measured against the center tap. Note they are of different polarization (180 degrees out of phase with relation to neutral) https://i.ibb.co/Jd04y8W/20210227-111949.jpg If you want to trip your breaker real fast, take that single ended probe and connect the grounded lead it to one of the legs.  |
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Posted: 5/20/2021 10:42:41 PM EDT
[#40]
Quote HistoryQuoted: In homes (US, maybe elsewhere?) power is supplied by a center-tapped transformer on the pole, which comes into the house. The center tap is "neutral", the other two legs are L1 and L2. Between L1 and Neutral and L2 and Neutral are 120V of potential difference. Between L1 and L2 there is 240V of potential difference, because their AC sine waves are 180 degrees out of phase from each other. (The sine wave of one is at absolute positive when the sine wave of the other is absolute negative) Neutral is bonded to ground at the entrance... if you measure from neutral to ground you should read 0V In commercial or 3-phase applications, 3 phases are supplied that are actually 120degrees out of phase from each other. (Generators make power by making 360 degree rotations..e.g. a full rotation.) In these installations each phase to neutral is 120V of potential difference... but between any leg, is only about 208V, since they are only 120degrees out of phase. Voltage is by-definition the potential difference between two points... you have to accept that with voltage you are always measuring the DELTA between two points. Yeah, thanks - I looked it up to avoid more dickhead replies. As usual, a simple picture makes it clear how the transformer splits the phase - a point that I believe most people who are not in the business get hung up on. |
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Posted: 5/20/2021 10:46:06 PM EDT
[#41]
Quote HistoryQuoted: And apparently they can be pretty complex to setup right ... something about where you put in the ground rods, etc. Of all the places to run into that, I learned it when reading about how to get 60hz mains hum out of audio recording/playback/equipment. Those hums are usually from "ground loops". Grounds really do not protect against lighting in residences anyway. They are there so that electrical devices that have METAL exteriors or parts are protected. The metal exterior is electrically connected to earth ground... that way if the device ever fails in a way where line voltage is touches the metal case, someone won't get shocked. (because electricity always takes the path of least resistance, and will flow to ground directly rather than flow through the person). My great-grandfather passed down his tools (he was a carpenter), in there was a drill with a METAL exterior case, but only has a plug with 2 prongs (neutral and hot)... with no ground, if the hot wire ever touched the metal case, the user would get shocked... the extra ground wire protects against this. |
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Posted: 5/20/2021 10:47:02 PM EDT
[#42]
Quote HistoryQuoted: The poles in a panel are not out-of-phase, it's all the same phase, but while one side goes + the other side goes - There's only 1ph in a resi single family dwelling. The CT in a xfrmer does not magically create a new phase. the reason USA residential power is called "split-phase" is because at the pole transformer the single phase primary is wound against a center-tapped secondary. the center tap is the neutral on your service drop, and the ends of the secondary are 180 degrees out of phase with one another. thus the two legs in the panel are 180 degrees out of phase with one other, with one primary advantage being that twice the power can be delivered with only a 50% increase in wiring cost. regardless of whether you term it a pole, a leg, or a phase, the fact that the two are 180 degrees out of phase means that the current carried by the neutral is only the difference (imbalance) of the two. if the L1 current = L2 current, the neutral current is 0. if the L2 current = 0, the neutral current is equal to L1 current. and so on. in no case does the neutral current exceed the L1 or the L2 current. again, this is a primary advantage of split phase power -- more power delivered with less copper/aluminum. |
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Posted: 5/20/2021 10:47:03 PM EDT
[#43]
The answer is simply the definition.
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Posted: 5/20/2021 10:49:58 PM EDT
[#44]
Quote HistoryQuoted: If you want to trip your breaker real fast, take that single ended probe and connect the grounded lead it to one of the legs. Quote HistoryQuoted: Quoted: Looks like this. This is one leg measured against the center tap.... https://i.ibb.co/DM8vncq/20201218-165623.jpg Here are both legs measured against the center tap. Note they are of different polarization (180 degrees out of phase with relation to neutral) https://i.ibb.co/Jd04y8W/20210227-111949.jpg If you want to trip your breaker real fast, take that single ended probe and connect the grounded lead it to one of the legs. If you want to plug your grounded scope probe directly into the wall, yeah, you could easily blow it up. That's why you use an isolation transformer. This is a 24/12/24 volt, center tapped transformer, IIRC |
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Posted: 5/20/2021 10:51:00 PM EDT
[#45]
Quote HistoryQuoted: In homes (US, maybe elsewhere?) power is supplied by a center-tapped transformer on the pole, which comes into the house. The center tap is "neutral", the other two legs are L1 and L2. Between L1 and Neutral and L2 and Neutral are 120V of potential difference. Between L1 and L2 there is 240V of potential difference, because their AC sine waves are 180 degrees out of phase from each other. (The sine wave of one is at absolute positive when the sine wave of the other is absolute negative) Neutral is bonded to ground at the entrance... if you measure from neutral to ground you should read 0V In commercial or 3-phase applications, 3 phases are supplied that are actually 120degrees out of phase from each other. (Generators make power by making 360 degree rotations..e.g. a full rotation.) In these installations each phase to neutral is 120V of potential difference... but between any leg, is only about 208V, since they are only 120degrees out of phase. Voltage is by-definition the potential difference between two points... you have to accept that with voltage you are always measuring the DELTA between two points. So this is why I failed electric motors. Cuz I still don't get this phase shit. |
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Posted: 5/20/2021 10:52:41 PM EDT
[#46]
Quote HistoryQuoted: the reason USA residential power is called "split-phase" is because at the pole transformer the single phase primary is wound against a center-tapped secondary. the center tap is the neutral on your service drop, and the ends of the secondary are 180 degrees out of phase with one another. thus the two legs in the panel are 180 degrees out of phase with one other, with one primary advantage being that twice the power can be delivered with only a 50% increase in wiring cost. regardless of whether you term it a pole, a leg, or a phase, the fact that the two are 180 degrees out of phase means that the current carried by the neutral is only the difference (imbalance) of the two. if the L1 current = L2 current, the neutral current is 0. if the L2 current = 0, the neutral current is equal to L1 current. and so on. in no case does the neutral current exceed the L1 or the L2 current. again, this is a primary advantage of split phase power -- more power delivered with less copper/aluminum. Quote HistoryQuoted: Quoted: The poles in a panel are not out-of-phase, it's all the same phase, but while one side goes + the other side goes - There's only 1ph in a resi single family dwelling. The CT in a xfrmer does not magically create a new phase. the reason USA residential power is called "split-phase" is because at the pole transformer the single phase primary is wound against a center-tapped secondary. the center tap is the neutral on your service drop, and the ends of the secondary are 180 degrees out of phase with one another. thus the two legs in the panel are 180 degrees out of phase with one other, with one primary advantage being that twice the power can be delivered with only a 50% increase in wiring cost. regardless of whether you term it a pole, a leg, or a phase, the fact that the two are 180 degrees out of phase means that the current carried by the neutral is only the difference (imbalance) of the two. if the L1 current = L2 current, the neutral current is 0. if the L2 current = 0, the neutral current is equal to L1 current. and so on. in no case does the neutral current exceed the L1 or the L2 current. again, this is a primary advantage of split phase power -- more power delivered with less copper/aluminum. ar-jedi is correct. with AC, by definition if "one side goes + the other side goes -" means they are out of phase. The picture someone posted above of the o-scope shows this perfectly. |
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Posted: 5/20/2021 10:54:23 PM EDT
[#47]
Quote HistoryQuoted: Looks like this. This is one leg measured against the center tap.... https://i.ibb.co/DM8vncq/20201218-165623.jpg Here are both legs measured against the center tap. Note they are of different polarization (180 degrees out of phase with relation to neutral) https://i.ibb.co/Jd04y8W/20210227-111949.jpg ETA, here is what both legs look like together leg to leg, no neutral (looks same as one leg to neutral) only difference would be a higher amplitude than just on leg to neutral, because the voltage is double..... https://i.ibb.co/DM8vncq/20201218-165623.jpg ETA again, finally got the pics right, lol Wow! Nerd went and confirmed this whole AC phenomenon. Bravo. |
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Posted: 5/20/2021 10:54:34 PM EDT
[#48]
Quote HistoryQuoted: So this is why I failed electric motors. Cuz I still don't get this phase shit. Dude, I ain't gonna lie... I'm digging back into 20 years of cob-webs to remember this from college... I've been working on DC and digital stuff so long I can barely remember! |
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Posted: 5/20/2021 10:55:15 PM EDT
[#49]
Quote HistoryQuoted: Looks like this. This is one leg measured against the center tap.... https://i.ibb.co/DM8vncq/20201218-165623.jpg Here are both legs measured against the center tap. Note they are of different polarization (180 degrees out of phase with relation to neutral) https://i.ibb.co/Jd04y8W/20210227-111949.jpg ETA, here is what both legs look like together leg to leg, no neutral (looks same as one leg to neutral) only difference would be a higher amplitude than just on leg to neutral, because the voltage is double..... https://i.ibb.co/DM8vncq/20201218-165623.jpg ETA again, finally got the pics right, lol Lol. I wasn't going to say anything... |
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Posted: 5/20/2021 11:00:13 PM EDT
[#50]
Quote HistoryQuoted: Those hums are usually from "ground loops". Grounds really do not protect against lighting in residences anyway. They are there so that electrical devices that have METAL exteriors or parts are protected. The metal exterior is electrically connected to earth ground... that way if the device ever fails in a way where line voltage is touches the metal case, someone won't get shocked. (because electricity always takes the path of least resistance, and will flow to ground directly rather than flow through the person). My great-grandfather passed down his tools (he was a carpenter), in there was a drill with a METAL exterior case, but only has a plug with 2 prongs (neutral and hot)... with no ground, if the hot wire ever touched the metal case, the user would get shocked... the extra ground wire protects against this. Not correct. The purpose of the green wire is to provide an uninterrupted pathway back to the low side of the transformer. 120 or 240 boots divided by an ohm or less equals plenty of current to trip the breaker. The ground wire exists to ensure that there is a low enough resistance between the source and the load to trip the breaker and clear the fault. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/bregnd.html |
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