Physics and History of Why USA uses 120 volts and not 220 volts
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Date: 2022-12-27
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Comments and reviews: 20
Karen
Three phase electricity.
Three magnets at the generator means three currents of the same voltage, but each is slightly out of time with the others. Each line gets its own transformer.
Homes are typically served by only one final transformer. A homes two hot wires come from the same transformer.
Industrial power differs in that the factory receives power from three transformers one from each of the phases created by the generator. Factories use the fact that the hot wires are slightly out of time with each other as a means to make motors spin. Think of each phase giving the motor a little kick in the right direction.
In one of the more common arrangements, the three step-down transformers are connected so that one end of the output wire is connected to the other two transformers. This creates one point in the system where voltages are the same. We call this the neutral point.
The other output wires, plus a wire from the neutral point, are run to the factory. In their panel you will find three hots and one neutral.
Since each of those 240v hots is slightly out of time with the others, you will measure only 208 volts between any two hots. Measure any hot to neutral, though, and youll find 120v.
There are other ways the power company can connect transformers to each other. Thats why you might find voltages such as 480, 277, 240, or 115.
Distance from the transformer matters. A house near the transformer will measure 125, while a house at the end of the street might measure 108.
Last post: Europe vs. the USA
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Three phase electricity.
Three magnets at the generator means three currents of the same voltage, but each is slightly out of time with the others. Each line gets its own transformer.
Homes are typically served by only one final transformer. A homes two hot wires come from the same transformer.
Industrial power differs in that the factory receives power from three transformers one from each of the phases created by the generator. Factories use the fact that the hot wires are slightly out of time with each other as a means to make motors spin. Think of each phase giving the motor a little kick in the right direction.
In one of the more common arrangements, the three step-down transformers are connected so that one end of the output wire is connected to the other two transformers. This creates one point in the system where voltages are the same. We call this the neutral point.
The other output wires, plus a wire from the neutral point, are run to the factory. In their panel you will find three hots and one neutral.
Since each of those 240v hots is slightly out of time with the others, you will measure only 208 volts between any two hots. Measure any hot to neutral, though, and youll find 120v.
There are other ways the power company can connect transformers to each other. Thats why you might find voltages such as 480, 277, 240, or 115.
Distance from the transformer matters. A house near the transformer will measure 125, while a house at the end of the street might measure 108.
Last post: Europe vs. the USA
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john
The cost is not about the transformers it is about distribution losses that increase with i2. Not sure if you covered it but Edison was an ego maniac and wanted to use DC while Tesla showed that Ac was the way to go. Edison was not even half the engineer of Tesla but a more conniving business man. 240VAC distribution losses are 25 % of that of 120VDC. Japan distribution network covers a smaller area so safety could be considered. That is why we use typically 115kV for long distance distribution. If you were to transfer power from Niagara falls to New York city with DC with the current wire sizes, less than 1% would get to your light bulbs and most would generate heat along the wires. I am not as informed as you about the details but I was always taught that 110 was more about the fight between AC and Dc and Tesla and Edison's little tiff. Edison was trying to promote his patents and Westinghouse was going to destroy him. That is likely the major factor here. Edison could care less about safety but used safety concerns to try derail a far superior technology that he could not refute on scientific terms.
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The cost is not about the transformers it is about distribution losses that increase with i2. Not sure if you covered it but Edison was an ego maniac and wanted to use DC while Tesla showed that Ac was the way to go. Edison was not even half the engineer of Tesla but a more conniving business man. 240VAC distribution losses are 25 % of that of 120VDC. Japan distribution network covers a smaller area so safety could be considered. That is why we use typically 115kV for long distance distribution. If you were to transfer power from Niagara falls to New York city with DC with the current wire sizes, less than 1% would get to your light bulbs and most would generate heat along the wires. I am not as informed as you about the details but I was always taught that 110 was more about the fight between AC and Dc and Tesla and Edison's little tiff. Edison was trying to promote his patents and Westinghouse was going to destroy him. That is likely the major factor here. Edison could care less about safety but used safety concerns to try derail a far superior technology that he could not refute on scientific terms.
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Karen
Step down transforming.
Since the generator has three magnets, it creates three phases. A phase is an electrical current with a time factor. Since that magnet passes wires one at a time, each wire carries current at a slightly different time.
Once the transmission wires reach a bank of transformers near the customer, the voltages are reduced to a manageable level. Now ask: What number is easily divided into the maximum number of whole numbers? Answer: 60. Lets look at some multiples: 60, 120, 240, 480. Look familiar?
Each coil in a transformer has (at least ) two connections: one in and one out. In the following examples, lets assume the voltage between these two wires is 240 volts.
If I attach a wire to the exact center of that coil, the voltage between this central wire and either of the other wires will be half of 240, or 129 volts. This is what typically serves your house. You have two hot wires with 240 volts between them, and a neutral that measures 120 volts to either of the hots.
Next post: Three phase
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Step down transforming.
Since the generator has three magnets, it creates three phases. A phase is an electrical current with a time factor. Since that magnet passes wires one at a time, each wire carries current at a slightly different time.
Once the transmission wires reach a bank of transformers near the customer, the voltages are reduced to a manageable level. Now ask: What number is easily divided into the maximum number of whole numbers? Answer: 60. Lets look at some multiples: 60, 120, 240, 480. Look familiar?
Each coil in a transformer has (at least ) two connections: one in and one out. In the following examples, lets assume the voltage between these two wires is 240 volts.
If I attach a wire to the exact center of that coil, the voltage between this central wire and either of the other wires will be half of 240, or 129 volts. This is what typically serves your house. You have two hot wires with 240 volts between them, and a neutral that measures 120 volts to either of the hots.
Next post: Three phase
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Karen
Voltage and current:
Current is created by passing a magnet over a wire. Voltage is determined by how many times that wire is wrapped around the magnet.
Use thick wire and you get lots of current but few volts. Use fine wire and you get little current but lots of volts.
Fortunately one coil of wire can induce electricity in another coil of wire. Place a coil of fine wire next to a coil of fine wire and you will transform high voltage/ low current into low voltage/high current.
Thats what transformers do.
Electrical resistance is determined by current alone; great current means lots of resistance. End result is that less energy comes out the end of a wire than what you put in.
Power companies beat this by greatly increasing voltage for transmission lines, then transforming it (stepping down) near the end. High voltage = less current = less lost in transmission. Kind of like getting better mileage when you drive slower.
Next post: Step down transformers.
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Voltage and current:
Current is created by passing a magnet over a wire. Voltage is determined by how many times that wire is wrapped around the magnet.
Use thick wire and you get lots of current but few volts. Use fine wire and you get little current but lots of volts.
Fortunately one coil of wire can induce electricity in another coil of wire. Place a coil of fine wire next to a coil of fine wire and you will transform high voltage/ low current into low voltage/high current.
Thats what transformers do.
Electrical resistance is determined by current alone; great current means lots of resistance. End result is that less energy comes out the end of a wire than what you put in.
Power companies beat this by greatly increasing voltage for transmission lines, then transforming it (stepping down) near the end. High voltage = less current = less lost in transmission. Kind of like getting better mileage when you drive slower.
Next post: Step down transformers.
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Kathy
I MADE A MISTAKE: I stated that if you add more light bulbs in parallel the bulbs will be dimmer because the resistance will go up. The light bulbs will be dimmer if more are added in parallel but not because the total resistance increases. In fact, the total resistance will decrease as they are in parallel. The bulbs are dimmer because more current is being drained from the generator and the internal resistance means that the voltage over the individual bulbs will decrease.
I am so sorry, I should have realized what was happening with a bit of thought. Also, now that it is up, I cannot edit my video (although I did add a little card in the corner.
Also, many of you were confused by my quick transition between Edison's 3-wire DC and Westinghouse's and European AC systems. I should have been more clear about when that transition happened, sorry.
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I MADE A MISTAKE: I stated that if you add more light bulbs in parallel the bulbs will be dimmer because the resistance will go up. The light bulbs will be dimmer if more are added in parallel but not because the total resistance increases. In fact, the total resistance will decrease as they are in parallel. The bulbs are dimmer because more current is being drained from the generator and the internal resistance means that the voltage over the individual bulbs will decrease.
I am so sorry, I should have realized what was happening with a bit of thought. Also, now that it is up, I cannot edit my video (although I did add a little card in the corner.
Also, many of you were confused by my quick transition between Edison's 3-wire DC and Westinghouse's and European AC systems. I should have been more clear about when that transition happened, sorry.
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David
I'm confused. Edison was a DC man, hence you have the edison split phase supply.
Single phase supply central earth /neutral.
So each 110 volt line is not actually AC but a pulsed 110 volt supply each pulse lasting half of the cycle then nothing for the other half cycle. Then you have a second similar cycle being the other half of a full cycle. But low and behold if you want more power you can use both phases togeather and not have a pulsed dc supply but full AC at 220v.
This same system is probably the reason for 60 cycles in the US to control the half phase flicker. In a full 240 ac system you have both the negative and positive peaks so out of a 230 v ac system at 50hz one has 100 lighting peaks much less noticable flicker.
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I'm confused. Edison was a DC man, hence you have the edison split phase supply.
Single phase supply central earth /neutral.
So each 110 volt line is not actually AC but a pulsed 110 volt supply each pulse lasting half of the cycle then nothing for the other half cycle. Then you have a second similar cycle being the other half of a full cycle. But low and behold if you want more power you can use both phases togeather and not have a pulsed dc supply but full AC at 220v.
This same system is probably the reason for 60 cycles in the US to control the half phase flicker. In a full 240 ac system you have both the negative and positive peaks so out of a 230 v ac system at 50hz one has 100 lighting peaks much less noticable flicker.
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Karen
You really ought to chat with a real electrician about this lets look first at how electricity is made.
Electricity is made by spinning a magnet inside a coil of copper wire. One magnet = one phase. Since a three magnet arrangement (6 pole) nests rather well, three magnets is the routine way to make motors and generators. Spin the magnets faster and you get a higher frequency.
USA: 60 minutes in an hour, 60 seconds in a minute 60 cycles per second seems natural.
France: Lets invent the metric system. 100 is a nice round number. Passing one pole of a magnet over a wire 100 times a second means you need to spin that magnet at 50 rpm. Hence, 50 cycles.
Next post on s about voltage.
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You really ought to chat with a real electrician about this lets look first at how electricity is made.
Electricity is made by spinning a magnet inside a coil of copper wire. One magnet = one phase. Since a three magnet arrangement (6 pole) nests rather well, three magnets is the routine way to make motors and generators. Spin the magnets faster and you get a higher frequency.
USA: 60 minutes in an hour, 60 seconds in a minute 60 cycles per second seems natural.
France: Lets invent the metric system. 100 is a nice round number. Passing one pole of a magnet over a wire 100 times a second means you need to spin that magnet at 50 rpm. Hence, 50 cycles.
Next post on s about voltage.
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Icaros
FYI Live and Neutral are AC nomenclature and have no relevance to DC systems. 2: 47, the lines would be 0v at the bottom, +110 in the middle and +220v between top and bottom. At about 5: 00, you begin talking about transformers which do not work with DC only AC. Japan is the only country to have both 50 and 60Hz split between the north and south. The point of three phase is that you can transmit power using 3 live conductors (using a Delta configuration) without a neutral thus saving a conductor. It is converted to Star configuration (as per your diagram, to recover the Neutral, normally done once down at consumer voltage level.
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FYI Live and Neutral are AC nomenclature and have no relevance to DC systems. 2: 47, the lines would be 0v at the bottom, +110 in the middle and +220v between top and bottom. At about 5: 00, you begin talking about transformers which do not work with DC only AC. Japan is the only country to have both 50 and 60Hz split between the north and south. The point of three phase is that you can transmit power using 3 live conductors (using a Delta configuration) without a neutral thus saving a conductor. It is converted to Star configuration (as per your diagram, to recover the Neutral, normally done once down at consumer voltage level.
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Kevin
Actually in North America we do have 220 it just gets split from the transformer to the house in 2 hot leads and a single neutral so one side of your main panel will be say HOT-A and the other side of the panel will be HOT-B and Neutral = Neutral and Ground = Ground, If you need a 220/240 circuit for an appliance in the house such as Stove, Electric Clothes Dryer etc. the HOT Leads from both sides of the panel are combined on the that circuit to bring it back to 220. that's how it works in Canada where I live.
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Actually in North America we do have 220 it just gets split from the transformer to the house in 2 hot leads and a single neutral so one side of your main panel will be say HOT-A and the other side of the panel will be HOT-B and Neutral = Neutral and Ground = Ground, If you need a 220/240 circuit for an appliance in the house such as Stove, Electric Clothes Dryer etc. the HOT Leads from both sides of the panel are combined on the that circuit to bring it back to 220. that's how it works in Canada where I live.
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history
The short answer is, it would be too expensive and time-consuming to switch over to 220V even though it would offer many advantages. There are new electrical standards on the horizon for LOW power devices like lights, modern TVs and so on because if you think about it there are really only a few devices in a modern house that require a lot of energy, such as refrigerator, oven, drier, hot water heater. Just about everything else can be powered by far less, especially today.
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The short answer is, it would be too expensive and time-consuming to switch over to 220V even though it would offer many advantages. There are new electrical standards on the horizon for LOW power devices like lights, modern TVs and so on because if you think about it there are really only a few devices in a modern house that require a lot of energy, such as refrigerator, oven, drier, hot water heater. Just about everything else can be powered by far less, especially today.
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james
Design engineer of 40+ years. PE registered. Multiple patents. Hands on fixer of many things electrical and mechanical, so not just a theorist.
But until my later years not that interested in history. This, Professor Kathleen, was great. But I will admit, I had to watch it twice for it to sink in! Oh, for the days when I could learn new things.
Why is that? Why can't we at 65 learn like an infant of 3? I wanna know.
There I go down another rabbit hole.
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Design engineer of 40+ years. PE registered. Multiple patents. Hands on fixer of many things electrical and mechanical, so not just a theorist.
But until my later years not that interested in history. This, Professor Kathleen, was great. But I will admit, I had to watch it twice for it to sink in! Oh, for the days when I could learn new things.
Why is that? Why can't we at 65 learn like an infant of 3? I wanna know.
There I go down another rabbit hole.
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Robin
Fascinating presentation. I live in the UK and in the 1960s, the domestic voltage was standardised to 240V AC single phase. At the time my house was on 220V so the electricity board had to replace all bulbs, fridges and washing machines so they could run on the higher voltage. It was amazing how long 220V bulbs would survive running at 240V before they burnt out. Later under EU regulations the voltage was reduced to 230V
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Fascinating presentation. I live in the UK and in the 1960s, the domestic voltage was standardised to 240V AC single phase. At the time my house was on 220V so the electricity board had to replace all bulbs, fridges and washing machines so they could run on the higher voltage. It was amazing how long 220V bulbs would survive running at 240V before they burnt out. Later under EU regulations the voltage was reduced to 230V
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Dan
Maybe you covered this elsewhere. Tesla developed alternating current not Westinghouse. Tesla developed 3 phase and a whole bunch of other phases. He sold out to Westinghouse. Edison and Tesla were rivals with Teslas system winning the day. The problem with DC is that the size of cables needs to huge to transport electricity longer distances. There are plenty of books explaining Teslas contribution.
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Maybe you covered this elsewhere. Tesla developed alternating current not Westinghouse. Tesla developed 3 phase and a whole bunch of other phases. He sold out to Westinghouse. Edison and Tesla were rivals with Teslas system winning the day. The problem with DC is that the size of cables needs to huge to transport electricity longer distances. There are plenty of books explaining Teslas contribution.
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Mathis
Amsterdam and Delft had 3x220 (230) Volts up till 2000 or even later. Just that nobody had issues when they went to 3x380 (400) Volt because they had 2 phases on the normal power outlets.
Just machines running on 3 Phases had to been set to 3x380 Volt.
Unfortunately I could not handle watching your vid because of your hands flashing through the screen. Please mask off your hands.
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Amsterdam and Delft had 3x220 (230) Volts up till 2000 or even later. Just that nobody had issues when they went to 3x380 (400) Volt because they had 2 phases on the normal power outlets.
Just machines running on 3 Phases had to been set to 3x380 Volt.
Unfortunately I could not handle watching your vid because of your hands flashing through the screen. Please mask off your hands.
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Edmund
No word about Tesla. He was a big promoter of AC while Edison was, for some reason, terrified of AC and pushed DC. Edison and Tesla put on a demo, with Tesla using AC and Edison using DC. Of course DC failed especially at the end of the line since there was way to transform DC into a higher voltage which reduced the amount of current required.
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No word about Tesla. He was a big promoter of AC while Edison was, for some reason, terrified of AC and pushed DC. Edison and Tesla put on a demo, with Tesla using AC and Edison using DC. Of course DC failed especially at the end of the line since there was way to transform DC into a higher voltage which reduced the amount of current required.
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JerryFacts
I live in Canada. My preference would be for North America to be on 220/240 Volts like the EU and most of the planet. A lot more efficient. The 115 to125 Volts is less efficient. At this point converting to 220 to 240 Volts cannot be done because of the huge cost and all the buildings and systems are wired for present system.
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I live in Canada. My preference would be for North America to be on 220/240 Volts like the EU and most of the planet. A lot more efficient. The 115 to125 Volts is less efficient. At this point converting to 220 to 240 Volts cannot be done because of the huge cost and all the buildings and systems are wired for present system.
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Karen
Europe vs USA
In truth, weve both agreed on 240volts as our basic voltage.
In Europe, their system has a 480v transformer with a neutral. From them you get a 240v hot and a neutral.
In the USA, you get two hots with 240v between them, plus a third wire as your neutral. Between either hot and the neutral measures 120.
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Europe vs USA
In truth, weve both agreed on 240volts as our basic voltage.
In Europe, their system has a 480v transformer with a neutral. From them you get a 240v hot and a neutral.
In the USA, you get two hots with 240v between them, plus a third wire as your neutral. Between either hot and the neutral measures 120.
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l_trr
I love America and the Americans, I spend a lot of time there because of my job, but I'd like to understand why they keep using those terrible plugs for electricity. they slip off at the slightest movement of the cable, and it is impossible to use them from the bottom up, in short, the European plugs are absolutely better.
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I love America and the Americans, I spend a lot of time there because of my job, but I'd like to understand why they keep using those terrible plugs for electricity. they slip off at the slightest movement of the cable, and it is impossible to use them from the bottom up, in short, the European plugs are absolutely better.
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SPARKY
Beware of 347 volts. It almost killed me. I was separating two wires with my insulated pliers. It grabbed me and I was shaking like a fish on a hook. My heart was beating faster. But I could not let go. Fortunately I bent my legs and my body pulled me off the wires. It is the most dangerous voltage on earth.
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Beware of 347 volts. It almost killed me. I was separating two wires with my insulated pliers. It grabbed me and I was shaking like a fish on a hook. My heart was beating faster. But I could not let go. Fortunately I bent my legs and my body pulled me off the wires. It is the most dangerous voltage on earth.
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Matt
I dont understand the fuss. I have nearly as many 220v outlets in my home as 110v. It is a matter of choice, and the option is there for most every homeowner in the US. 110v may be more convenient for appliances that have smaller power requirements, but it is not the only option.
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I dont understand the fuss. I have nearly as many 220v outlets in my home as 110v. It is a matter of choice, and the option is there for most every homeowner in the US. 110v may be more convenient for appliances that have smaller power requirements, but it is not the only option.
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