110 or 120

[Nathan]

What is the standard voltage for a wall socket? 110v or 120v? And also is it 220v or 240v for one of those big sockets.

[Bob in CT]

It depends. It should be 240V and 120V, but the actual voltage varies. I have a power center (you plug stuff into it) and it shows voltage. It'll vary day by day and sometimes minute by minute.

[Toller]

On an unused circuit, not too far from your breaker box, it should be 120v. Acceptable tolerances are 114v-126v. If it outside of that, 110v for instance, they have your transformer set wrong.

A particularly distant outlet, or a circuit being used, might show lower voltages without being incorrect.

[Terry]

Agree: last time was checking something we measured 119 volts on one side (or leg) and 121 on the other side. Across both sides it was IIRC 238 volts or something. That was in a building fed with single phase, 115-0-115, during the day with no load on the circuits. But as said it varies. BTW anybody know what are the +/- percentages are in North America? In continental Europe, the UK for example, while domestic supply is a nominal 230 volts the standard allows a certain percentage plus and a certain percenatge minus. So the actual voltage at any moment could be more than, say, 240 volts or as low as, say, 216!

[Bill]

This is one of those perennial questions. The answer is that it has varied over time. When I was a boy during the 40s it was 110v. Then when I went to work in electronics in the late 50s it was 115v. I know that because we had to check a lot of equipment over its normal operating range. The normal operating range at that time was 115v +/- 10 v. Now the normal line voltage is 120v. And of course 240 is just twice the 120.

So a lot of the confusion over 110/220 vs. 120/240 is just that the voltage has changed, but a lot of people haven't changed the way they refer to it.

I wonder if they are going to keep moving the voltage up? I know several places I have lived, in different parts of the country, seem to be carrying the voltage at about 122v for the past 20 years or so.

Bill Gill

[Pop Rivet]

The actual spec for the generating companies is 106 to 126 Vac. Normally, under normal neighborhood loadings, the voltage will measure about 120Vac. Urban areas often run

110 to 115. You'll seldom see it as low as 106 but I do know areas, Sioux Falls SD for instance, where 106 Vac is not unusual, but those are the exceptions. From 106Vac down to 95Vac is considered "brownout" conditions and often is used in rolling brownouts. The ac line voltage supposedly is never allowed to drop below 95Vac; if it gets that low, they are supposed to cut the power to preserve not only their own equipment but electric motors throughout their customer grids. Momentary surges up to 132Vac are allowed for short periods of time. This is so they can get their grids balanced after a shutdown and when, because the power has been off, the loads are going to be heavy for some number of hours. As those hours pass and the loads balance out, some areas may experience up to 132Vac for several minutes at a time. This is why, if you check the numbers, switching power supplies are often designed for and labeled 95 - 135V ac input.

Hth

Pop

120v? And

[The Masked Marvel]

Assuming North America: 120/240 +10% / -15% (or in commercial w/ 3 phase often 120/208 and sometimes additionally 277/480 3 phase for lighting).

Motors are usually designed for 115, 200, 230, (or 200/230) & 460 to allow for voltage drop in wiring and slight brownouts.

127V is found in parts of Brazil, 100V in parts of Japan, 240 in UK, 220 in much of continental Europe -- though the trend is to shift up or down to 230V >

[The Masked Marvel]

The expected limit spec for equipment design is +10% / -15% in USA so the limits should be 102V-132V and 204V-264V (or 177-229 for 208V nominal).

The target delivered voltage spec (brownouts and other abnormalities excepted) is tighter than that: might be +/-6% (113-127)?

[Pop Rivet]

You forgot the 50/60 Hz mix , esp in Japan

commercial w/ 3 phase

for lighting).

200/230) & 460 to allow

240 in UK, 220 in

up or down to

or 120v? And

voltage varies. I

shows voltage. It'll

[ns]

To be a real pain in the butt , the output of the generating station is in the range of a few kV. Then you have transformers boosting the voltage for transmission to a few

100s of kV. The residential/commercial distribution is the range mentioned below.

[Seth Goodman]

ANSI C84.1 says ± 5% as delivered (i.e., at your line drop), +6%, -13% at the point of utilitizaton.

NEMA recommends appliances be built to tolerate ± 10% variance.

More than you ever wanted to know about this:

[Pop Rivet]

AndI thought I gave a lot more info than was needed ! Seriously, that's a good point - I do know people who think there's LV in them thar power line thingies. I had one guy argue with me that they MUST NOT be very high voltage, or they would have insulation on them! I couldn't help it, I just admitted that maybe those were stepup, not stepdown transormers on the poles outside and moved on. .

Pop

generating station is

transmission to a few

mentioned below.

126 Vac

or

sockets.