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# Simple electrical question

#1
09-11-11, 07:19 PM
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Join Date: Feb 2010
Location: U.S.A.
Posts: 248
Simple electrical question

No Big deal, but I have often wondered why American household voltage has different descriptions---
110V
115V
120V

Can someone explain this?

#2
09-11-11, 07:47 PM
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Location: USA
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Back when Westinghouse and Edison were arguing which was better AC or DC Westinghouse set his AC at the same voltage as Edison's DC. My best guess is because at the time most electric was used for lights so the same light bulbs could be used on AC or DC.

Over the years as DC faded into distant memory voltages were raised, probably because the higher the voltages, especially transmission lines, can be smaller. Nominal single phase domestic voltage is now 240v with 120v derived from a grounded center tap.

#3
09-12-11, 04:25 AM
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Join Date: Apr 2007
Location: Near Buffalo, NY
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The voltage coming in to your house is supposed to be 120VAC (240VAC). The devices that plug in may be rated 110, 115, or 120. Quick searches tell me that the lower-rated devices are designed to run on lower voltage because of voltage drop across the lines (distance from the transformer, house wiring, extension cords, etc.). No big deal ... it's all within the acceptable +/-10% tolerance. Trouble starts when the voltage drops to less than 95, or hits more than 130.

#4
09-12-11, 10:40 AM
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It's basically historical values that have persisted in common language. A very long time ago 110V was the standard, then 115V. For the last probably 50 years or more 120V has been the standard nominal voltage in most of North America. I suppose you might be able to find some areas where 110V and 115V were used more recently, but to my knowledge it's been a long time.

By nominal that means that the actual voltage is near 120V, but rarely exactly 120V. Under normal circumstances it will be within about 5%, under severe circumstances (bad weather, heavy load, extreme distance, etc) it may be as much as 10% off. All appliances are designed to accommodate the anticipated range of voltage.

110-125V all means the same thing, as does 220-250V.

#5
09-12-11, 11:23 AM
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Join Date: Feb 2010
Location: U.S.A.
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THANKS---That is an excellent explaination.
Originally Posted by ibpooks
It's basically historical values that have persisted in common language. A very long time ago 110V was the standard, then 115V. For the last probably 50 years or more 120V has been the standard nominal voltage in most of North America. I suppose you might be able to find some areas where 110V and 115V were used more recently, but to my knowledge it's been a long time.

By nominal that means that the actual voltage is near 120V, but rarely exactly 120V. Under normal circumstances it will be within about 5%, under severe circumstances (bad weather, heavy load, extreme distance, etc) it may be as much as 10% off. All appliances are designed to accommodate the anticipated range of voltage.

110-125V all means the same thing, as does 220-250V.

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