why 115v and not 230v

[severach]

Re: why 115v and not 230v

http://en.wikipedia.org/wiki/War_of_Currents

At the time it was felt that 100 volts was not likely to present a severe hazard of fatal electric shock.

100v was the voltage chosen for DC which came out first. For AC to be accepted it had to be compatible with at least some DC equipment already in place. 110v AC was completely compatible with lights and some equipment. Many corded power drills can run from DC or AC. AC and transformers allowed 220v to be broken up into two legs of 110v for existing equipment and devices handled by consumers. 220v could be used to increase the efficiency of equipment with high power requirements and little shock hazard. Over time 110v was increased to 120v to get more power through the same transmission lines. The voltage increase was small enough that most existing equipment was compatible.

I can place my fingers across 120v just for fun. I won't try that with 240v. The problem isn't that the current doubles. The problem is that the higher voltage makes more paths available. Paths that would not conduct at all at 120v may conduct at 240v. You'll probably live if you get tangled up with 120v. You probably won't if you walk on the 480v supply rails of a gantry crane or fall on the power rails of a subway train. 120v, 480v, what's the difference, right? What can 500,000 volts do for you?

For example, at 480v a spark plug is an open circuit. At 50,000 volts a spark plug is a conductor. If something doesn't conduct BHG says "what if we tried more voltage?"

I ask why we don't all use 3 phase? 3 phase offers a big efficiency increase for electric motors and 480v radios work great in the bath tub.

[mariushm]

Re: why 115v and not 230v

It's historical reasons... Edison started to distribute electricity at DC 110v but Tesla being the genius that he was calculated that three phase 240v AC at 60 Hz would be the best for power distribution.

But Edison didn't want to say Tesla is right, he thought DC was better... he even did public campaigns where he was killing animals with AC current to prove AC power was not safe and crap like that.

In the end, he had to accept and go with AC voltage and 60 Hz but he stuck with 110v claiming it is safer, but the reality was probably that he didn't want Tesla to be right. Tesla eventually also gave up and let it be 110v.

See this, it's really entertaining: http://theoatmeal.com/comics/tesla

So yeah, 240v is better as you can use thinner wires. There is an increase in efficiency due to the high voltage, but modern power supply use active pfc boosting the voltage to around 400v so it's not that more efficient.

quoting wikipedia:

Choice of voltage

The choice of utilization voltage is due more to historical reasons than optimization of the distribution system—once a voltage is in use and equipment using this voltage is widespread, changing voltage is a drastic and expensive measure. A 230 V distribution system will use less conductor material to deliver a given amount of power because the current, and consequently the resistive loss, is lower than for a 120 V system. While large heating appliances can use smaller conductors at 230 V for the same output rating, few household appliances use anything like the full capacity of the outlet to which they are connected. Minimum wire size for hand-held or portable equipment is usually restricted by the mechanical strength of the conductors. Electrical appliances are used extensively in homes in both 230 V and 120 V system countries. National electrical codes prescribe wiring methods intended to minimize the risk of electric shock and fire.

Many areas using (nominally) 120 V make use of three-wire, single-phase 240 V systems to supply large appliances. Three-phase systems can be connected to give various combinations of voltage, suitable for use by different classes of equipment. Where both single-phase and three-phase loads are served by an electrical system, the system may be labelled with both voltages such as 120/208 or 230/400 V, to show the line-to-neutral voltage and the line-to-line voltage.

If you think 110v is a pain, go to Japan where some regions have 110v, some 127v... some have 50Hz and some have 60 Hz ... again historical, as UK was in charge of reconstruction of the country after the war so they brought generators with them from the 50Hz based Europe.

[Rulycat]

Re: why 115v and not 230v

I believe 230V is more efficient for SMPS but 115V is safer.

[goontron]

why do they use 115v in the u.s. instead of of 230v it pisses me off when my crap don't work!
and in Australia i took us 115v crap and connected it to my mains to watch it smoke, but now to get Aussie power i have to go phase to phase and filter and regulate and use a VFD to get 50hz! so WTF!