# 110V, 115V, 120V, 125V, 220V, 250V confusion

• posted on January 7, 2005, 6:39 pm
I am confused as to how voltage is designated. Line voltage is described with so many numbers. Is there actually a standard on what should be incoming voltage in a residential house?
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• posted on January 7, 2005, 6:42 pm
120 plus or minus 5%.
There are many stories about where the other values come from; I haven't heard one that sounds credible.
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• posted on January 7, 2005, 6:53 pm
Again, I'm hungover and tired - but ius it possible they are a spillover from multi phase vs single phase? http://www.faqs.org/faqs/electrical-wiring/part2/section-10.html
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• posted on January 7, 2005, 7:34 pm

http://nonstop.compaq.com/TechPubs/PDF/Power_Requirements/TPAPPA.pdf
In the USofA, You can always get three-wire service, with 2 feeds that are nominally 120V to ground, and 240V from each other, at 60 Hertz. The voltage tolerances vary by jurisdiction from 2-8% of the nominal voltages. In many places, you can also get 4-wire residential service, still with 120V on each hot to ground, but with each of the three lines at 208V from each other.
Most of Eurasia appears to use 2-wire service with 220V to ground, or variations thereof.
--Goedjn
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• posted on January 7, 2005, 7:42 pm

A lot of residential outlets will measure 125 V. The trend over the years has been to higher voltages as it is more efficient.
110 Volts originated with the original Edison systems where the voltage supplied was 110 VDC. The reason he picked this voltage was a compromise between safety and efficiency and the ability to match a suitable incandescent lamp filament with a useful life expentancy and a suitable output level in lumens. Minimizing excessive voltage drop and the cost of expensive copper conductors was also a consideration.
When AC replaced DC, the 110 voltage stayed the same. In the 1950's this increased to 120 volts. Many devices were still rating stamped 110v. 115v. or 120v.
Beachcomber
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• posted on January 7, 2005, 7:49 pm
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• posted on January 8, 2005, 12:10 am
Beachcomber wrote:

You know I remember it being 110V, but I could not remember when it changed or why. Thanks for the history. I was there in the 50's and just old enough to know it was 110V.
--
Joseph Meehan

26 + 6 = 1 It's Irish Math
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• posted on January 10, 2005, 9:48 pm

I remember the 50s and one of those lessons a little kid learns - from my recollection, the 110 felt about like 120 did later in life when I should have known better!
"Sparky"
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• posted on January 7, 2005, 8:15 pm
toller wrote:

FWIW, here's a pointer to an "INTERIM OPINION ON EMERGENCY VOLTAGE REDUCTION MEASURE" that was up before the California state PUC with regards to lowering the nominal line voltage to 117VAC during times of electrical energy shortage.
http://www.utilityregulation.com/content/orders/02CA13831.pdf
Makes sense that with a lower voltage the demand for power decreases. However, this only follows for resistive devices. Constant power loads (like motor-driven equipment) would demand greater current and cause increased conductor loss as well as increasing risk of failure to the equipment.
Dunno if they ever implemented this; at my house the voltage gyrates quite a bit throughout the day anyway so it's hard to tell what the "nominal" is.
later, L
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• posted on January 8, 2005, 2:08 am

One solution if there is not enough power to go around is to lower the line voltage. This is called a brownout.
Another solution is to have rotating blackouts as California did a few years ago.
Remember that this is only for California where most electrical consumers are at the far end of the (transmission) line. They pretty much don't like large conventional power plants in California (be they nukes, coal-fire, hydro-electric dams, or gas fired units) and are not building a whole lot more.
Because of this, a lot of California power comes from outside the state (Oregon, Washington, British Columbia) in the north and Hoover Dam and other sources (Nevada - Arizona) in the south. There is only one Nuke in the state and quite a few medium and smaller sized hydro-electric dams in the mountains. Geothermal also makes a small contribution.
Beachcomber
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• posted on January 8, 2005, 2:48 am
Beachcomber wrote:

Well, they don't like building them close to the populated areas. But there are quite a few ancient plants in the populated areas of So Cal. Look for those tall stacks at the beaches and such.

Known as the Pacific Intertie. Palo-Verde Nuclear in Arizona. Four Corners coal fired in New Mexico. Don't know of much coming out of Nevada, Las Vegas sucks up enough power!

Two that come to mind right away. San Onofre for SCE and Diablo Canyon for PG&E

Big Creek is a decent size project but as with any hydro, it doesn't run year round. Especially during droughts!

As does wind,

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• posted on January 8, 2005, 2:08 pm
Mark and Kim Smith wrote:

...
...
And 850 MWe of perfectly good idled capacity at Rancho Seco...