November 21, 2014

Why does UK/USA use 110/120V and others use 220/240V

My girlfriend asked me this question this morning and since I explained it to her, I though why not write an article and explain to everyone of you about why does USA/UK use 110/120V and others use 220/240V.

United States distribution system actually provides a 240 volt residential service in the form of two 120 volt conductors and a neutral conductor. You can see this if you look inside your breaker panel.
When a load is applied from either 120 volt conductor to the neutral (as is the case for typical receptacles, lights, and so forth) it is using 120 volts.
However, when a load is applied from one 120 volt conductor to the other, without using the neutral, the voltage being used is the sum of both 120 volt conductors (240 volts). This is the case for many water heaters, air conditioners, electric furnaces, clothes dryers, and so forth.

So equipment that is connected to strictly 240 volts is connected with only a two wire cable plus a safety ground wire. (For example 240 volt base board heaters use this.) The only time a cable with three wires plus safety ground is used is if 120/240 volts is needed in the equipment. (For example kitchen ranges or washing machines which have time clocks or programmers that require only a 120 volt feed.)

So the answer is that both ‘some of the world’ and the U.S. distribute 240 volts to homes, apartments, shops, offices, and many other types of buildings.

It seems like the difference you are talking about is that on the non-U.S. systems, their receptacles are 240 volts, while ours are 120 volts. One reason is that lower voltages tend to be safer, which is why you are receiving 240 volts at the home instead of the thousands of volts generated by the power plant.

In terms of power production – all power is the same. It is then transmitted over High Voltage cables – usually above 10K Volts. The power is then stepped down before it reaches our homes.

U.S, Japanese and some other countries receive 110V in the form of 2 wires – 1 Live and 1 Neutral
Some may argue that the US is behind or has just managed to stay afloat with this old system longer.
The US is at 120 volts, not 110 volts. It was increased sometime around the 1950s.

The historic reason for 110 volts was due to the DC power systems created by Thomas Edison. I think he chose 110 volts because that is what his light bulb worked on. Later on these systems were converted to AC so you didn’t need a power plant on every corner but the voltage wasn’t changed so existing lighting didn’t need to be replaced (they didn’t care if they got AC or DC)

An interesting question is why the rest of the world did start using 110 volts. How did 220/230/240V get started over there? 
The US system theoretically could be made as good as (slightly better, actually) than the European system with no infrastructure change, except to houses themselves. US houses get 240 volts at the panel. If wall outlets all were fed with 240V you’d have the lower current and higher power advantage of the European system and it would be safer too, since each “hot” would still be only 120V from ground (not 240V) which keeps the reduced shock hazard advantage. Of course it is still possible to touch the two hots.

As one has stated above, it was Thomas Edison who promoted the use of (then) 100 volts as some tragic experiences in the early days of power distribution showed that 100 volts was not usually lethal for a shock. Remember that in the early days, bare wires were strung though ceramic insulators, both exterior and interior, and so there were many more shock hazards present. As technology advanced, good, long life insulation was wrapped on conductors.

Speaking from personal experiences, one as a child, I am glad that the few shocks I’ve experienced were with 120v., not 220v. power.

Just remember it’s not the volts that kill, it’s the current (the amps).
Yes, but at 240 volts your body’s resistance will draw twice the current and that may well be over the threshold to kill you. In countries in Europe and elsewhere, where 230 volts is the general standard mains supply voltage for domestic houses, offices, factories, etc., they have to make sure that their wiring systems are very safe by using high quality insulation and wiring methods for all wiring upgrades and new work.

For additional safety the most recent wiring regulations insist that a Ground Fault Current Interruptor (GFCI) or a Residual Current Device (RCD) must be included in the main Consumer Distribution Unit (breaker box in US parlance) to cut the supply very quickly if any significant difference is detected between the currents flowing in the live (hot) and neutral wires.

An RCD works in a different way to the original very simple Ground Fault Current Interruptor (GFCI). An RCD will trip if there is any significant difference between the currents flowing in the live (hot) and neutral wires. A simple GFCI would trip only if any significant current is detected flowing in the main Earth (Ground) wire to the actual Earth (or Ground) spike. Note: GFCIs now operate exactly the same as RCDs.
In up-to-date domestic installations in the UK no actual Earth “spike” is used. Instead the protective safety wiring (or casing) of the incoming mains supply cable is used because that is most likely to be reliably “grounded” to the Earth.

That is different to US and Canadian standards and other countries’ which use the same. In those countries the incoming mains supply is two “hot” wires supplying 240 volts balanced around “Ground Potential” which is always 0V. (Zero Volts). An Earth Spike is used at each property (house, apartment, office, factory, works site or whatever) to provide a common Neutral (i.e. the “White” wire) for the two resulting 120 volt “hots”. One “hot” is coloured “Black”, the other one is coloured “Red”

The Second explanation is:

The existence of the various standards has been largely the result of local politics and historical accident

The system of three-phase alternating current electrical generation and distribution was invented by a nineteenth century creative genius named Nicola Tesla. He made many careful calculations and measurements and found out that 60 Hz (Hertz, cycles per second) was the best frequency for alternating current (AC) power generating. He preferred 240 volts, which put him at odds with Thomas Edison, whose direct current (DC) systems were 110 volts. Perhaps Edison had a useful point in the safety factor of the lower voltage, but DC couldn’t provide the power to a distance that AC could.

When the German company AEG built the first European generating facility, its engineers decided to fix the frequency at 50 Hz, because the number 60 didn’t fit the metric standard unit sequence (1,2,5). At that time, AEG had a virtual monopoly and their standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and only after World War II the 50-cycle standard was established. A mistake, however.

Not only is 50 Hz 20% less effective in generation, it is 10-15% less efficient in transmission, it requires up to 30% larger windings and magnetic core materials in transformer construction. Electric motors are much less efficient at the lower frequency, and must also be made more robust to handle the electrical losses and the extra heat generated. Today, only a handful of countries (Antigua, Guyana, Peru, the Philippines, South Korea and the Leeward Islands) follow Tesla’s advice and use the 60 Hz frequency together with a voltage of 220-240 V.

Originally Europe was 120 V too, just like Japan and the US today. It has been deemed necessary to increase voltage to get more power with less losses and voltage drop from the same copper wire diameter. At the time the US also wanted to change but because of the cost involved to replace all electric appliances, they decided not to. At the time (50s-60s) the average US household already had a fridge, a washing-machine, etc., but not in Europe.

The end result is that now, the US seems not to have evolved from the 50s and 60s, and still copes with problems as light bulbs that burn out rather quickly when they are close to the transformer (too high a voltage), or just the other way round: not enough voltage at the end of the line (105 to 127 volt spread !).

Note that currently all new American buildings get in fact 240 volts split in two 120 between neutral and hot wire. Major appliances, such as virtually all drying machines and ovens, are now connected to 240 volts. Mind, Americans who have European equipment shouldn’t connect it to these outlets. Although it may work on some appliances, it will definitely not be the case for all of your equipment. The reason for this is that in the US 240 V is two-phase, whereas in Europe it is single phase.

Roughly speaking, to operate a particular appliance requires a particular amount of POWER, which (at least for resistive loads) is current times voltage. If you double the voltage, you draw half the current to achieve the same power. The primary advantage of lower current is that you lose less power in the wires feeding current to the appliance (or you can use smaller, cheaper wires for the same power loss rating). On the other hand, the higher voltage is somewhat more dangerous if accidentally touched or if there is an accidental short circuit. Some experienced electricians are relatively casual about touching 110 V circuits, but all respect 230 V. (This constitutes a “don’t-try-this-at-home thing, though–it’s quite possible to get a fatal shock or start a fire with 110 V!) Current trends are toward the use of even lower voltages (24 V, 12 V, 5 V, 3.3 V…) for any devices which don’t draw much total power to increase safety. Power is rarely distributed at these lower voltages; rather it is converted from 110 V or 230 V by a transformer at the earliest opportunity. Even in North America, 220-240 V is commonly used in residential appliances for
most high-power electrical appliances (ovens, furnaces, dryers, large motors, etc.) so that the supply current and supply wire size can be smaller. Higher power industrial applications often use 480 V or more. And, of course, transmission lines use progressively higher voltages as the distance and total power go up (22,000 V for local distribution to 1,000,000 V for long distance lines).

via: Some content via StraightDope

Supplementary Reading: [1], [2], [3]

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