All About Circuits Forum What is the Actual Household Voltage - 110, 115, 120, 220, 240?
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#1
09-19-2006, 02:12 PM
 Erin_2006 New Member Join Date: Sep 2006 Location: Miami Posts: 5
What is the Actual Household Voltage - 110, 115, 120, 220, 240?

HI,

I've been reading sooooo many different voltages for household current here in the US. What is the real number you should go by or do people put the different voltages because it varies so much? I've seen references to 110V, 115V, 120V, 220V, 240V. (same frequency though = 60Hz).

(just curious)
Thanks!
#2
09-19-2006, 03:07 PM
 beenthere Senior Member Join Date: Apr 2004 Location: Missouri, USA (GMT -6) Posts: 15,815 Blog Entries: 10

Hi,

It is a bit confusing. The voltages expressed are just approximate. The most common pairs are 110/220 and 120/240.

Due to line drops, the actual voltage into your home will vary with the distance from the transformer on the pole. It may be several volts above 120 if close, and as low as 107 if some distance away.

Just to cross your eyes further, the actual standard is supposed to be 117/234 VAC.
#3
09-19-2006, 03:49 PM
 Erin_2006 New Member Join Date: Sep 2006 Location: Miami Posts: 5

Yup...that definitely crossed my eyes. Million dollar question: How do you get a measurement of voltage coming out of your wall socket without feeling like your sittin on ol' sparky?
#4
09-19-2006, 05:51 PM
 beenthere Senior Member Join Date: Apr 2004 Location: Missouri, USA (GMT -6) Posts: 15,815 Blog Entries: 10

Hi,

You put your meter on the floor, set to measure AC volts. Poke the meter leads into the slots and see what it reads. Move slowly. You won't get bit.
#5
09-22-2006, 02:44 PM
 EEMajor Member Join Date: Aug 2006 Location: USA Posts: 67

Quote:
 Originally Posted by beenthere Hi, It is a bit confusing. The voltages expressed are just approximate. The most common pairs are 110/220 and 120/240. Due to line drops, the actual voltage into your home will vary with the distance from the transformer on the pole. It may be several volts above 120 if close, and as low as 107 if some distance away. Just to cross your eyes further, the actual standard is supposed to be 117/234 VAC.
+1.
Yeah, there is no one voltage that you will find everywhere. Like he said, it will vary with distance, type of wire used, temperature of the wires, corrosion on the connections between your outlet and the generator, etc...

It will even vary slightly with time of day, depending on the load that the grid has during the day. Summer and Winter voltages will vary as well.

However, it should never be off by more then 5% of the rated loads, and never off by more then 2-3% for lighting loads. If you are worried that an appliance isn't functioning correctly due to voltage issues, read the specs on the applicance, and calculate the percentage.

For example, if you have an toaster rated at 120V, multiply 120 by .05 to get 6. Now subtract 6 from 120, (120-6) = 114. This means that 114VAC is the lowest that this toaster should run on. Maybe a toaster isn't a great example, since it will run on just about anything, but you get the idea.
#6
04-18-2007, 12:50 AM
 CATV Junior Member Join Date: Apr 2007 Location: NE Penna Posts: 11

I use a status monitor system that monitors the AC mains across 800 miles of CATV plant in NE Penna. I get readings every 15 minutes from over 150 power supplies. The readings vary from about 112 to 124 volts. Each device can vary over time by about 5 volts.
#7
04-18-2007, 01:47 AM
 Tube Tech Junior Member Join Date: Jan 2007 Posts: 46

Back in the 70s, a trade association investigated this very thing. They found that the median voltage is 117.

Here's a hint: the two major 3-phase power sources are 208 and 480. 208 is what you get from 2 120 VACs 120 degrees out of phase. 480 is a multiple of 120.

So, 120 VAC in theory, all over the voltmeter in real life.
#8
06-19-2007, 01:09 PM
 dhivyaraman New Member Join Date: Jun 2007 Location: Chennai Posts: 7

In india the household voltage is 220V to 250V for single phase and frequency of 50Hz. But in US the supply is 110V,60Hz and some other country also. U know one thing, some products which are going to be exported to such countries, the will design for supply of both 230V,50Hz and 110V,60Hz. This is to make the product to work in both supply range.
#9
06-19-2007, 01:15 PM
 dhivyaraman New Member Join Date: Jun 2007 Location: Chennai Posts: 7

In india household voltage is 220V to 250V,50Hz. But some other countries like US, supply voltage is 110V,60Hz.Some products which are going to be exported in such countries are made to work in both sypply range
#10
06-20-2007, 12:04 AM
 subtech Senior Member Join Date: Nov 2006 Location: Middle of USA GMT -6 Posts: 115

Believe it or not, there are standards here in the US.
In the electrical power industry (read Power Company), the standard voltage for almost all single phase services is 120/240. The reason that you will most likely measure something slightly different at an outlet in your home is because of economic reasons. There must be an allowable tolerance in the voltage at which you are served. It is not impossible to keep things at 120 plus or minus 1 volt, but it would be very, very expensive to do so and of course as you know, it is not necessary either. Almost all equipment that you have in your home or business is designed to operate with a voltage that fluctuates plus or minus 5% from "center of band" or 120 Volts. That same plus or minus 5% holds true for services at other voltages as well. If you are a large industrial customer who requires 480 volt service for your large motors and equipment, that equipment is designed with that tolerance in mind. Right now in the USA, there are almost 500,000 people working hard to make sure that the voltage where your toaster is plugged in is as close to 120 as we can get it. (within those economic constraints of course)
People monitor those voltages 24/7/365 along with alot of other things.
We absolutely do NOT want you to wake up some morning and have to do without your toast, coffee, and whatever. ('Cause you're pretty grouchy without that coffee...)
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 Tags 110, 115, 120, 220, 240, actual, household, voltage

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