The majority of people who deal with indoor distribution voltages are in residential environments: usually laypersons and often children. 220 V is 4 times as dangerous as 110 V (voltage squared -> power). Whereas many people have experiences of surviving a shock from 110, I would doubt that so great a percentage shocked by 220 live to tell about it. So, I see it as a trade-off between safety and cost.

Distribution power loss (Isqr.R) would be four times at 110V than 220V, yet many countries/companies can effort loss, and giving more importance to safety(110V very less dangerous), than the system efficiency uses 110V distribution . The conductor size(cross section)required would be larger(double) for same load, hence installation cost(fixed cost) would be more.

Safety, as Derek and Bhupendra suggest, is the main advantage of 110V, I think. But in countries that use 110V, homes are also provided with 220/230V, for the heavier loads, such as water heaters, electric stoves, electric driers, and central air conditioning systems. So it's not a big deal.

The cables for the 110V loads tend to be 14 gauge wire, typically limited to 15 amps. There may possibly be some 20 amp 110V outlets, fed by 12 gauge wire. The heavier 220/230V outlets are fed by gymongous cables.

Oh by the way, I was surprised, growing up, that so many adults had never experienced an electric shock. It seemed unreal. And yes, 220V shocks are more severe than 110V, although I can say with some confidence that they too are survivable!

In India, the distribution is 220V. I knew, how peoples, are afraid of electric shock. If you don't wants to give credit to countries/companies using 110V as distribution voltage, it's O.K!!!!!.

If I touch a live wire I prefer it is a 110V rather than a 220V :-)

What really matters to one's life when touching a live wire is the amount of current passing through one's body. Typical human body resistance with dry skin is in the order of 1000 to 2000ohm. Hence, we are looking at 50 to 200mA of current passing through the body. Not high enough to cause burnt but sufficient to cause heart failure. Hence, 110V is safer than 220V.

if we are  reducing the volatge level 110 then we directley affected the losses. Any domestic equipment losses are directley proportional to voltage. All are desigened by and working on electromagnetic principle. Due to this, we will increase the effecincy of system  by reducing the losses at 110 v

.

I already said that,power loos((I)(I)R) will be four times more, for the same equipment(resistance) , as current flow would be doubled with 110V system than 220V system, for same power demand. Hence efficiancy of system will, not increased but, reduced considerably with 110V than 220V. Domestic equipments losses(W=(I)(I).R)), will increased to double though coil resistance may half , as current wii doubled(V=I.R), for 110V than 220V for same power capecity, as I said.As RRRV would be more, large breaking capecity, breakers wiill be needed.

In India, the distribution system is not 220V as Bhupendra has stated. The 3-phase distribution line voltage is 400V 50Hz nominal, which makes the 1-phase supply 230V. However, in both the 1-ph & 3-ph supply systems, a person standing on the ground and touching only one wire receives a maximum shock corresponding to the peak value of 230V, which is 1.732x230 = 325V ! So many of our electricians receive an accidental shock in buildings and survive. Yet, several deaths do take place when unsuspecting victims grasp live points accidentally. I agree that 110V or similar voltage will reduce shock hazard, while demanding more conductor cross sectional area (and hence higher cost per meter of wiring). It is a question of compromise. Countries like USA have 3-wire dual voltage systems (120V-0-120V) at all homes, with the 120V (120V-0) used for all lighting, fan and appliance (that can be touched and can pose shock hazard) and the 240V (120V-120V)used for higher power loads like heaters, air conditioners (that is likely to be fitted in inacessible heights or locations).

I was telling my staff/student to develop practice to work only with one hand(right), if rubber glows are not availble, in India(to reduce chaces to complete circuit through heart)..

in general there are two systems in the world with respect to indoor (domestic) voltage and frequency:  110 V @ 60 hz and 220V @ 50 hz. 

using 110V @ 60 hz is more safere with respect to 220 V @ 50hz.

some countries use both systems like Sudia Arabia

The only thing which I can think is the safety while 110 has more current and frequency so more losses+ the effect of harmonics losses.

Furthermore, changing from previous system to a new system is costly and they prefer to keep it. In Japan they used 50Hz system and connect it in a point to 60 Hz so that they could develop 50Hz system.

Well ! accoirding to non scientific opinion: This voltage level is mostly used in USA and some parts of Japan ! and I think it has the same reason that they are not using the metric system ! 

In truth, 110-127 VAC was used in many European countries too, years ago, for the "normal" loads. For instance even in the 1960s, Italy and France had the same two cylindrical prong wall plugs and sockets, for normal loads, capable of 6 amps at 110-127 volts, one side hot and the other neutral.

There are still some unlikely places (that is, not in the Americas) that have 120-127V domestic power, such as Belarus(!?), Spain, Somalia, Japan (actually 100V), South Korea, Saudi Arabia.

Side note on power frequency. For the same power rating, a 60 Hz transformer is smaller than a 50 Hz transformer.

This article

http://www.school-for-champions.com/science/ac_world_volt_freq.htm

explains that Europe also adopted 110V domestic power, until after World War II. I know that Italy and France didn't make the shift to 220V until well into the 1960s, depending on the city. The change was phased in gradually. The article also states that the "most efficient" values should be 60 Hz and 220V, although that is rare for normal domestic appliances.

So in short, the original choice of 110V was made by Thomas Edison, and many countries used that initially, or the 115 or 127 variants.

This seems to be a good comprehensive listing of power standards. Domestic power is tabulated starting on page 20.

http://www.legrand.be/sites/default/files/Power_book_03_0.pdf

The arguments about safety are just spurious. In normal installations there is no risk of ever touching a live wire. The reason why 110V and similar voltages are still in use is simply that it is very expensive to upgrade networks to 220V. 

I expect that in the future there will be greater use of low voltage DC systems as the increased use of photovoltaic roofpanels and lower cost battery systems makes this practical and economic in domestic installations.

Great thanks to you all professors. The discussion is highly useful. In conclusion, and as an output of the discussion, am I right to say reasons of still using the system of 110V despite its high cost and high losses, are mostly safety and the high cost of shifting to 220V system.

Yes, Salah. Your conclusions are correct. 110V is safer, but 220V will have less loss on the wires as current is reduced (for the same power).

NO. I'm sorry. When it comes to safety the limits to voltage exposure are very clear :

in a dry environment the maximum safety voltage is 25 VAC, in wet conditions it is 12 VAC.  Any voltage above that is able to  provoque death by muscle contractions (fibrilation when it the heart is concerned). You can also die because your chest's muscles are seized by the action of the current.

The muscles respond to CURRENT and current is the concequence of a voltage applied accros an impedance (the body for instance).

So why some people use 110 and others 220, why 50Hz or 60Hz... this is history and technical choices made by governments.

For energy efficiency, the best is HVDC : a DC high voltage, but this is another topic.

OK Dr. Bergogne. This means that the 110VAC is not that safe, as the safe voltage is 25 VAC dry, and 12 VAC wet. Previously we put a conclusion that  safety and the high cost of shifting to 220VAC system are the reasons of keep using 110VAC. Your answer weakens the safety side. Although still the 110VAC is saver than 220VAC, is that enough to still use the 110VAC. Now It is obvious that, cost of shifting to 220VAC is the main cause not to leave 110VAC. Actually the shift to 220VAC is not affordable. How can all distribution system be rebuilt? How can all load readjusted. Many units in each load should be changed. that is very difficult.

Sorry again, but I think that discussing whether 110 VAC is safer than 220 VAC is like comparing the lethal  capability of a 10cm long blade knife to a 20 cm long blade knife.

To answer the initial question : the  110VAC system has no advantage over the 220VAC system. The only reason why 110VAC it is in use is that it was there at first. Changing to 230VAC is a political choice.

Distribution efficiency, of 230VAC, is considerably high compare to 110VAC system as I discussed.Yet 110VAC system is in existence,and no need to changed it, immediately as is, quite more safer. There is nothing like the, comperesion of knife with long or short blades, thanks. 

Great thanks doctors for the interesting discussion. Reasons for using the 110VAC are now clear.