USA & elsewhere different stds????

gpigeon
gpigeon Registered Users Posts: 34 ✭✭✭
Afaik the domestic line V in the USA is 120 whereas everywhere else it is 240. Correct? If so, why? How did this come about? Advantages/disadvantages of each?
Does the US have a MEN (Multiple Earth Neutral??) system where an Earth conductor is run to each appliance?
I recall working on a job in Papua New Guinea where a whole mine processing plant was shipped from the US and we had to change out all the 3ph motors because you guys run a 50Hz system and the rest of us use 60Hz.
On the mechanical side of things....British screw threads are 55 deg angle and the NC & NF threads are 60 deg. And 1/2" BSW (Whitworth) is 12 TPI where 1/2" NC is 13 TPI. Someone is just trying to be difficult!
I had heard that some of these differences date right back to the US war of independence.
Has the US progressed toward metrication?

Comments

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    edited May 2022 #2
    That is a long and somewhat interesting story.

    Most folks don't know that the U.S. split phase system was originally started by Thomas Edison DC system in lower Manhattan NY.  Which is interesting and odd considering the rivalry between Thomas Edision DC system and Nikola Tesla AC system.

    The first lower Manhattan low voltage DC system had problems with complaints about lights dimming when too many folks turn on their lights due to voltage drop.  To solve this with least amount of extra copper wiring to already installed system, Edison decided to add a third wire and split the users on two different branches with one original common negative return wire.  This three-wire system turned into the AC split phase system when AC power took over.

    As to which is better 240vac single phase or 240/120v split phase, that is highly debated.  Split phase may be considered safer for low power residential outlets since it has lower peak voltage relative to ground.  It can also provide some benefits to lightning strikes.

    Multiple earth grounds can cause problems with return current (neutral) being shared between neutral and ground wiring.  Unless there is an actual fault, you don't want ground wiring to carry any current.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Here is a discussion (mostly friendly  :# ) about the 120 vs 240 VAC issue:

    https://www.quora.com/Why-does-USA-have-120-voltage-standard-and-rest-of-the-world-have-220-voltage-standard?share=1

    For the most part, it appears to go all the way back to Edison and Carbon Filament lamp. At that time, around 100-110 VDC was optimum for the technology at the time. It also allowed the use of battery banks to help supply current with the DC Generators.

    The problem with DC--"Low voltage and high current" with no ability to step up or down line voltage for transmission (no DC Transformers). And that ment that DC power generating plants could only send "useful amount of DC current" for a 1 or 2.

    Edison was a great experimental based designer/engineer. Tesla was campaigning for AC power systems (transformers, induction motors, poly-phase motors, etc.) and he was a math genius. To understand and design AC power systems--There is a bunch of math involved--Which Edison was not nearly as conversant in (the math):

    https://en.wikipedia.org/wiki/War_of_the_currents

    When Tesla won the "war", in the US, it was a fairly easy conversion from three wire DC (+110/neutral/-110 VDC) to 3 wire 110/220 VAC (110/N/110 VAC or 110/220 Split phase power).

    And the first large scale AC hydropower dam at Niagara New York was 25 Hz 2 phase 4-wire power. Later 3 phase power was :

    https://edisontechcenter.org/Niagara.htm

    There is lots of history here to read--If you are interested.

    Why 50 vs 60 Hz...

    https://www.electrical4u.com/why-supply-frequency-is-50-hz-or-60-hz/

    Originally, commercial power ranged 16.75 Hz to 133.33 Hz ...

    https://www.quora.com/Why-does-England-Europe-use-standard-frequency-50-Hz-instead-of-60-Hz-when-the-last-is-better?share=1

    There are good and bad reasons for both 50 and 60 Hz as a choice... Less flicker at 60 Hz and smaller transformers. At 50 Hz transformers are more energy efficient.

    In the end, many systems were designed for the voltage/frequency needed/best for the application:
    , Electrical engineer, radio ham, computer networking engineer
    , M.S. Electrical Engineering & Electronics, University of Southern California (2020) and 
    Samwel Mwashumbe
    , Bachelor Electrical Eng. Electrical Engineering & Electrical Power Systems, Mbeya University of Science and T…
     · Author has 505 answers and 1.4M answer views
    What is the reason behind choosing 50/60 Hz and not above?
    The choice of an optimum power frequency depends on three things; two that change over time and one that doesn’t:The specific application.Technology.The fundamental laws of physics.Let’s start with #3. The efficiency of power transmission by wire decreases with increasing frequency for two main reasons:Skin effects force AC currents toward the surface of a conductor.Wires radiate electromagnetic energy much more effectively at higher frequencies. This is great for building antennas, not so great for building a transmission line.So purely from a basic physics standpoint, the optimum AC power line frequency is zero Hz, i.e., DC.DC also has the advantage of a 1:1 peak-to-RMS voltage ratio. Since the insulation on a power line has to withstand its peak voltage, DC uses insulation more effectively than AC. (Yes, square-wave AC also has a 1:1 peak-to-RMS voltage ratio, but this involves carrying an infinite number of harmonics — which reintroduces the disadvantages just given of high frequencies.)So why didn’t DC become the standard despite fundamental physics? Thomas Edison tried very hard, but he ran into considerations #1 and #2. The efficiency advantages of high voltage and (relatively) low current transmission apply to both AC and DC, but during the War of the Currents between Edison’s DC and Westinghouse’s AC there was no practical DC transformer. So AC won by default.But what frequency AC? Too low, and light bulbs will flicker. (Except for DC, of course, but that wasn’t an option without a workable transformer.) Higher frequency transformers are also lighter and smaller than low frequency AC transformers carrying the same power, which is why the unusually high frequency of 400 Hz became the standard in aviation. Airplanes are also much smaller than terrestrial power grids, so transmission losses aren’t much of a problem.Large electric motors run more efficiently on lower AC frequencies, particularly the brush-type “AC/DC” type long used in electric traction (railways) because of the need to continuously vary speed. Many electric railways settled on relatively low frequencies for this reason, e.g., 25 Hz for the southern Northeast Corridor in the US and 16 2/3 Hz in much of central Europe. DC is even better, and many urban railways (e.g., subways and trams) use it, but again the advantages of high voltage AC won out when significant distances were involved.But 50 and 60 Hz were both reasonable compromises for most general purpose users, which is why they became the worldwide standards. Why not just one? Because one was as good as the other, and there was no compelling reason to junk a lot of perfectly good equipment that can otherwise last a very long time.If we could do it all over again from scratch with today’s technology, a very strong case can be made that electric power systems could and should be entirely DC. Thanks to high power semiconductor electronics, we now have practical “DC transformers”. They actually “chop” the DC into very high frequency AC so it can be stepped up or down with a (very small and light) transformer, then immediately converted back to DC at the new voltage.This has already been done for decades on certain long distance transmission lines, especially those carrying very large amounts of power very long distances, undersea or underground.The same electronics make it possible to drive the simple and rugged AC induction motor at whatever speed you want from a power supply at any frequency, including DC. This technology is the basis of modern electric and hybrid vehicles, and it has largely taken over railways too.And with the incandescent light bulb being rapidly replaced by CFL and now LED lighting, both of which use electronic power supplies, DC is again the natural — though they too can adapt easily to just about any AC supply frequency.
    I think I remember from one of my engineering classes--That the older European AC power generation system could not reliably be spun fast enough for 60 Hz--So 50 Hz was chosen for standardization (could not find conformation with a quick search).

    "I recall working on a job in Papua New Guinea where a whole mine processing plant was shipped from the US and we had to change out all the 3ph motors because you guys run a 50Hz system and the rest of us use 60Hz."

    You have that wrong (or typed it wrong)--In North America (and many others places) we use 60 Hz.

    And because most of North America now uses 120/240 VAC split phase 60 Hz power--We do have both 120 and 240 VAC available. But 240 VAC in homes is mostly used for higher power appliances (electric stove, water heater, electric drier, A/C and Heat Pump systems, etc.).

    But you will find 120/208 VAC in many office parks in Northern California. That is because our local utility PG&E feeds 120/280 Y (Wye) 3 phase power to those light industrial and commercial locations (bit of a pain to make sure you get 208 vs 240 VAC for those locations).

    And for larger locations with 480 VAC power, there are 277 VAC circuits typically used for industrial scale lighting of buildings (one phase of 480 Y (Wye) power.

    For homes--Older home may have 30 or 60 Amp 120/240 VAC. Newer homes 100-200 Amps. And now with electric vehicles, folks are starting to upgrade to 400 Amp 120/240 VAC service (an electrician I know has some high end clients adding 2x 400 Amp services for charging several Tesla cars).

    And today--There are now High Voltage DC transmission lines (fewer losses vs AC transmission lines) that have converter/inverters at each end. Also works well for sharing power between "networks" (i.e., western power grid sharing power with mountain power grid--Don't have to "phase lock" 60 Hz between them (the AC/DC/AC conversion allows them to run at 60.01 vs 59.99 Hz without issues when load sharing).

    https://en.wikipedia.org/wiki/High-voltage_direct_current

    Whitworth wrenches (sizes) were weird. Nothing (metric or English) would fit. Had an old Datsun (Nissan) pickup that I could use metric or US wrenches on--And they all fit perfectly (they had something like 3 different bolt head sizes for most hardware)

    Regarding Metic vs inch/foot/yard--Which is "better":

    https://transparentmath.com/2017/07/03/why-the-metric-system-is-not-always-superior-to-the-imperial-system/
    When it comes to feet and inches the imperial system uses a base 12 system, so instead of counting by 10’s (as in the metric system) you count by 12’s.  One foot is 12 inches, so two feet is 24 inches, three fee is 36 inches and so on.   While it may appear to be more difficult to count by 12’s than 10’s, the advantage that 12 has over 10 is in its divisibility.  Twelve can be divided by 2, 3, 4, and 6 (these numbers are called “factors” of 12), ten can only divided by 2 and 5.  In our daily lives being able to divide things up evenly easily is a huge plus.  For example if you had 12 slices of pizza you could share it evenly with 2 people ( 6 slices each), 3 people (4 slices each), 4 people (3 slices each) or 6 people (2 slices each).  On the other hand you had 10 slices of pizza you could only share it evenly with only  2 people(five slices each) or 5 people (2 slices each).   Therefore a foot unlike a meter can be cleanly divided by two , three and four – which for a carpenter or tailor makes it the better unit to work with.
    There are lots of reasons why imperial system does work easier for construction, mechanical engineering, etc...

    People are pretty practical... They use what works for their needs.

    Standardization comes later. 

    https://www.npr.org/sections/thetwo-way/2017/12/28/574044232/how-pirates-of-the-caribbean-hijacked-americas-metric-system

    One reason this country never adopted the metric system might be pirates. Here's what happened:

    In 1793, the brand new United States of America needed a standard measuring system because the states were using a hodgepodge of systems.

    "For example, in New York, they were using Dutch systems, and in New England, they were using English systems," says Keith Martin, of the research library at the National Institute of Standards and Technology.

    This made interstate commerce difficult.

    ........

    The secretary of state at the time was Thomas Jefferson. Jefferson knew about a new French system and thought it was just what America needed. He wrote to his pals in France, and the French sent a scientist named Joseph Dombey off to Jefferson carrying a small copper cylinder with a little handle on top. It was about 3 inches tall and about the same wide.

    This object was intended to be a standard for weighing things, part of a weights and measure system being developed in France, now known as the metric system. The object's weight was 1 kilogram.

    Crossing the Atlantic, Dombey ran into a giant storm.

    "It blew his ship quite far south into the Caribbean Sea," says Martin.

    And you know who was lurking in Caribbean waters in the late 1700s? Pirates.

    "These pirates were British privateers, to be exact," says Martin. "They were basically water-borne criminals tacitly supported by the British government, and they were tasked with harassing enemy shipping."

    The pirates took Joseph Dombey prisoner on the island of Montserrat, hoping to obtain a ransom for him. Unfortunately for the pirates, and for Dombey as well, he died in captivity.

    The pirates weren't interested in the objects Dombey was carrying. They were auctioned off along with the rest of the contents of his ship.

    Latest metrification push from US government... Probably simply folks did not want to listen to our politicians push metrics onto the American population. Last "major" metrification program:

    https://usma.org/laws-and-bills/history-of-the-united-states-metric-board#locale-notification

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • gpigeon
    gpigeon Registered Users Posts: 34 ✭✭✭
    Many thanks "RC" and Bill for your in depth replies. Yes, it is a very interesting subject.
    You guys take it easy. Cheers. Bill W.