100V Vs 240V


Thread Starter

Ayis Iacovides

I would like to have your kind answer on the following: Why does europe support a 240 V system and U.S. a 110 V one? Are there advantages one one over the other? Is it a safety thing, for humans? I am taking a class At University of Arizona in electric circuits and I had the chance to ask my instructor on the previous, which bothers me over some time , but we could not answer, so your kind answer would be appreciated if you have the time and the willingness to do that. Thanking you in advance, I remain, Ayis Iacovides. [email protected]

Alan Rimmington

Both have advantages, 110v is relatively safer to humans, but the lower voltage means that power devices draw need to draw a higher current, more than double, eg on 110v a 3kW load would take 27amps, however on 240v a 3kW load would take 12.5amps, thus smaller cable sizes/switch gear can be used for the same load. The other advantage of 240v is that this can be easily stepped down using a transformer to say 110v, although step-up transformers can be obtained they are less efficent and produce a lot of heat. With the advent of ELCBs the risks to humans from 240v is greatly reduced.

Christian Felde

My guess would be that it just ended up being that way (?).. Why do they drive on the left side in the UK? 110V would also be a little more secure maybe.. You do, on the other hand, get a higher voltage loss with 110V than with 230V on the same cable. I'm sure there are other things too..

Alex Mueller

I think this is just historically. But personally I prefer the 240V because you can safe on wiring cost when you use smaller wires. I don't think there is any increase of danger from 110 to 240. Both voltages are high enough to kill you when you sit in a bath tub. But it would be a lot easier when the US would start to use the same standards as the rest of the world does. Alex Mueller
The problem is not safety, that's sure. Using a higher voltage for controls (i.e. 230 V) you obtain, generally speaking, less ampere for the same power (I hope you know). That's better for all relays, circuits, wire and so on. That's the only reason for prefering higher voltage. In Europe, unlikely, often we use 24V-50hz standard (especially in Italy and England). Ciao

Kirk S. Hegwood

Which standard 120V, 208, 240, 380, 460, 480 or 575V? Which ones did I miss? As a designer and builder of controls, from S. America to USA to Canada to the UK, it all depends what parts are locally in stock at the customer site that determines my design. Kirk S. Hegwood President Signing for Hegwood Electric Service, Inc. [email protected] Phone: 770-447-8853 Fax: 770-447-5310

Hakan Ozevin

That's a very clever and deep question. I can answer to three aspects of it: 1. Safety: The shock hazard depends on the effect of the electricity flows through human body: a) It can burn the body, b) It can make a heart attack. For (a) we can say that the level of being burned depends on the heat energy "consumed" in the body and it can be expressed as V2xt/R. Here, R is the resistance of the body and from finger to foot of a dry one it is assumed to be 1 KOhm in average (fatty people are more resistive). Therefore, how much a body is burned depends on time and voltage applied to the body. However, at low voltages (up to say 400 V) V2xt is *usually* less enough not to make someone die from burning (It is assumed that the victim is rescued by someone else or throws himself away in a logical time - within seconds). At high voltages (from say 20 kV), the shock is too much that the body is thrown away from the source. Thus time (t) is very small. This explains why there are so many survivors from who had shocked by lightning(*). Therefore, medium voltages are the most dangerous levels for this case. (Disclaimer: Those what have written here are given for reference purposes only. Please do not try it at your home! :))) For (b), dangerous level for a heart attack (fibrillation) is defined with the current through the internal organs and assumed to be 80 mA for a healthy person and 60 mA for some other cases (old people, children). Therefore both 110 V or 230/240 V are dangerous even for a dry body. This explains why still there is a standart of 60 V (for example for elevator buttons in my country). Please do not forget that even 10 mA can give a hazard to someone with heart problem, or neurological disorder. Therefore even 12 or 24 V can be a problem, but with less risk. As a result, safety is a problem of body resistivity connected with the voltage level, but not limited to 110/230 V choice. 2. Economy: As voltage increases, copper losses decrease and in addition power transmitted per copper weight increase. Therefore higher voltage levels provides economy. 3. History: Power generation leaders are Edison (dc) and Westinghouse (ac). Voltage levels we are using today are coming from their choices or the generators they had. You can check the history from Internet. (It may be interesting for you to know that 20 years ago in Istanbul, where I live, half of the city was fed by 110 V and the rest by 220 V.) I believe that those standarts are for those uninformed people of the 19th century, who was unconsious about the hazards of electricity. Today, we have baby locks for the plugs, fault current protectors in most modern houses and the rest who are using electricity are aware about the hazards of it, thus 230/240 V should be increased to higher levels. This is necessary for a more green environment. Higher efficiency=less losses=less pollution Best regards, Hakan Ozevin (*): You may ask why those people do not die from a heart attack as told in (b). The human skin is much less resistive than the organs. Thus, in case of a lightning falling, current almost completely flows through the skin. The victim has skin burns, but no heart attack, if he was healthy and dry. If he is fat, he has more chance. Please note that when making the definition of the limit for a heart attack hazard, resistance of internal organs are assumed to be the same as the body average. This gives an extra safety range.
In truth, the U.S. frequently uses 240v but is that it is grounded at the center-tap producing 2) 120v 'legs'. How are the European 240v 1-ph systems referenced to ground? Bill Marsh ICD

Anthony Kerstens

240VAC is used in North America for lighting and other purposes, but not for consumer electrical items. And actually, I was thinking it would be nice if the rest of the world got with the North American way. :) Anthony Kerstens P.Eng.
In response to Christian Felde's first question: Left-side driving is related to the location of the sword carried by the knights of old. Got the above from a book about "imponderables!" Regards, Phil Corso, PE Trip-A-Larm Corp (Deerfield Beach, FL)

Michael Griffin

It's not the voltage differences which cause the most problems, it's the frequency. In the late 1940s we changed from 25 Hz to 60 Hz - I think the reason was to make trade with the US (in electricity and electrical goods) easier. It's too bad we didn't pick 50 Hz instead - then the world would have been a step closer to a single standard. At this time there is so much installed base that it would be very expensive to convert to 50 Hz. At the time, the conversion was paid for by Ontario Hydro as part of an organised program. The original 25 Hz standard came about by accident. An early generating plant was originally intended to be a compressed air plant, and the owners changed their minds to make it an electrical plant after the turbines were ordered. (Compressed air used to be distributed by pipeline to power various industries. You can still see the old pipelines running around the countryside near Cobalt, in northern Ontario.) In this generating plant, rotation speed and possible generator pole counts only gave certain possible frequencies, and 25 Hz was more or less arbitrarily chosen. Once 25 Hz was established, subsequent generating plants needed to maintain compatability if they were to sell to the same customers. In Japan, I understand they use both 50 and 60 Hz, and 100 and 120 volts in different parts of the country. By the way - around here we use a nominal 120 volts, not 110. I had thought that 110 as a nominal voltage was obsolete pretty well everywhere in the 60 Hz area. I guess I was wrong. ********************** Michael Griffin London, Ont. Canada [email protected] **********************
the european system uses three phase 400v, phase to phase is 400v and the phase to neutral is 230v. the neutral could be solidly grounded at the transformer. rgds leelock
This statement is not exactly true in regards to consumer goods. Most consumer items are 120 VAC but stoves, dryers, and air conditioners are commonly 240 VAC and the supply to houses is 120/240 VAC. Bill Mostia ======================================================= William(Bill) L. Mostia, Jr. PE Independent I &E Consultant WLM Engineering Co. P.O. Box 1129 Kemah, TX 77565 [email protected] 281-334-3169
Most common European standards use three phase, 380 V line voltage, and that means 3 X 220 phase Voltage ( any phase to grounded neutral ) Vitor Finkel [email protected] P.O. Box 16061 Tel (+55) 21 285-5641 22221.971 Rio de Janeiro Brazil Fax (+55) 21 205-3339
I believe the Europeans leave there 220V ungrounded, prefering GFIs to CBs or fuses to clear a ground fault. IIRFC, the Aussies typically use 120V that is centertap grounded for their standard voltage, so each leg is 60V to ground. Bob Peterson
Bob, Actually Australia is a 415v 3ph distribution system, with a 240v 1ph, and the star point grounded (generally). However there are variations on some rural areas with a 480v 1ph distribution system centre tapped to ground. In Western Australia, I believe, the voltage is slightly higher at 250v 1ph. There has been talk in changing to a 400v 3ph, 230v 1ph system in the future. Cheers, Trevor Ousey Kalangadoo, South Australia.

Jacek Dobrowolski

That's our (European) phase to ground voltage. (400 V phase to phase). Regards Jacek Dobrowolski

Jacek Dobrowolski

>>Which standard 120V, 208, 240, 380, 460, 480 or 575V? Which ones >>did I miss? Well, in fact you missed some of other standard voltages :) Sorry, I couldn't resist writing this. Regards Jacek Dobrowolski

Jeffrey W. Eggenberger

>My guess would be that it just ended up being that way (?). Why do they drive on the left side in the UK? > >110V would also be a little more secure maybe.. > >You do, on the other hand, get a higher voltage loss with 110V than with 230V on the same cable. > Never a voltage loss. Voltage is always conserved. I^2 R loss is what I think you mean (Power loss). The higher the voltage, the lower the current. Since the power loss is the square of the current, keeping the current down lowers power loss. However you still get inductive losses, that is why the new standard will be DC!

Morten Nilsen

More clarification: Residential lighting is 120 VAC. Lighting in industrial and commercial environments can be either 120 or 240 VAC, but is quite often 277 VAC (1 leg to neutral of a 3 phase, 480 VAC system). Morten Nilsen