In a thread I started in alt.home.repair (1920's wiring), a knowledgeable fellow (Bud) asserted that 208 V/3 ph dominates the country. Yet, I don't believe I have *ever* seen/heard anyone in these two ngs reference 208 V, other than to ask about operating a 208 V machine at 240. Other than me, in NYC, which *does* use 208 V..
Who else here has 208 V? Where are you located? What is your impression of the relative predominance of 208 vs. 240, from other people you know?
And, fwiu, even in places that are "barely" a part of NYC, like outer Queens, Staten Island, they have a mix of 208/240.
Yup. All the residential I've ever seen (and that would be on the west coast) has been 240 single phase center tapped. The utility provides it by putting a distribution transformer's primary between
2 phases of the 3 phases on the top of the power pole.
That said, I can easily imagine a neighborhood that was once predominantly commercial but now residential being 208/120.
Post WWII commercial and industrial buildings that I have seen have all been 208/120 3 phase or 480/277 3 phase.
Pre WWII are whatever they are. I've seen open delta and balanced delta with no neutral.
I live in a rural area east of Gilroy and have 240V 3 phase. I lost a Fanuc servo drive a few years back. The Fanuc tech. said that 240V was about the upper limit of what they like to see. Haven't lost any electronic stuff since then so I thinking it was probably a weak component............fingers crossed!
Of course I was barely out of warranty when the servo went. $3K for what was more than likely a few dollars worth of stuff.
I have 240V three phase here only because I'm in a residential neighborhood and have an open delta service. 120/208 is common around here for true 3 phase in industrial parks. Bigger power users go for 277/480V.
For new construction and/or power installation, you can have anything you are willing to pay for. My business is located in a light industrial area and the standard supply is 208/3. To get 480, we have a BIG transformer. The primary transformer feeding our building is rated 208/3 at 215 KVA. Our suite has three meters feeding power to us at 200 amp each. The rest of the building has a single 200 amp meter for each suite. The HID lights are fed off the same circuit, but are only single phase.
We are located in Central Oregon. That power design is typical of all but so called heavy industrial zoning.
Really high voltages are used to generate, transmit and use in large equipment. Here, I will only cover the "low voltage end of the spectrum, because that is what you want to know about. And, oh yeh, we are talking about the USA, not Europe, etc..
208 volts is what you get across one phase of a "Wye" connected 3 phase system. This is usually a 4 wire (plus protective ground) system. The nice thing about it is that if you go from any phase lead to the neutral lead, you automatically get 120 volts. So, if you are in an industrial situation, where you have a lot of 3 phase running around, it is easy to get 120 volts for general appliances. A "Delta" configured 3 phase system has only 3 wires (plus protective ground. The voltage across any two phases is 240. There is no nuetral, so there is no way to get 120 volts without using a transformer.
That's industrial and power distribution stuff.
For most residential power, the power company may use moderate voltage delta or wye on the poles that go by your house. Often, they send only one phase of "whatever it is" to each part of a community. Out here in the country, it is 14,400 volts. In a suburb where I once lived, it was
7800 volts.
Now for the answer to your question (as I see it, anyway): The "usual" thing they do (residential) is to use a transformer on the pole to reduce the line to 240 volts. They put a center tap in the transformer and that becomes the neutral (white wire) in your house. You get 3 wires coming into your house: 2 "Hot wires", that are black and one neutral wire that is white. The voltage across the 2 hot wires is 240 and the voltage across either hot wire and the neutral wire is
120 volts.
So, unless you have 3 phase power somewhere in the building where you are, you are unlikely to have 208 volts available. I say it this way because, if you work in an NYC skyscraper, etc., anything is possible.
Last disclaimer: These voltages are all approximate. The last I remember was that "120" is really meant to be: 117 vac +/- 10%, or 105 volts to 129. The same tolerance would apply to the 208 and the 240.
We used to has some weird wild leg delta 240 3 phase here years ago, but it all has been replaced with 208 3 phase. Fargo, ND here. Seems to ne that 208 three phase is the current trend, unless you want 480 3 phase. Greg
I live in a rural area west of Bakersfield..and I get 240-250 volts. One of my phase converters (on my Gorton Mastermill) really doesnt like it over about 242vts..and goes into alarm simply sitting there when the power is high. Many is the day in summer time that I couldnt use the mill until late at night when t he power drops below 242 volts.
And Ive called PG&E..commonly known as Pacific Greed and Extortion...and complained..and I always get blown off because its "within 10% +/-"
Gunner
"I am for doing good to the poor, but I differ in opinion of the means. I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. In my youth I travelled much, and I observed in different countries, that the more public provisions were made for the poor the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer." -- Benjamin Franklin, /The Encouragement of Idleness/, 1766
This is not unsolvable. How much current are you drawing?
You need a transformer that has a line voltage primary and a secondary rated for the phase converter's input. Then you wire the secondary IN SERIES with the primary feed of the phase converter.
For example: your converter draws 20 amps. You buy a 240v in/6V out transformer. I'll skip my usual ASCII-graphics attempts, but there are three junctions:
Line A + PC in
Line B + Secondary #1
PC in + Secondary #2
Plus power to the transformer primary.
You need to test it first. You may get 242+6v or 242-6v as output. Swap the two transformer leads to get to the lower.
This is called buck-boost and searches on that term should yield graphics.
Given that you can likely use 6-12 volts; you should find a variety of surplus transformers that will fit your needs; just be sure the secondary current rating is equal to or greater than your draw.
ps: usually line voltage goes UP at night, and down in the summer!
Add a 'buck' transformer to lower it some. A high current 12 volt transformer with its secondary connected in series, but out of phase would give you about 238 volts when the line is 250 volts. of course, the primary is connected to the AC line before the secondary. The secondary of the transformer has to handle the full current of the load, but some old battery charger transformers are big enough. Just make sure to check the phasing before connecting the load.
Ayup..Ive got a buckboost setup out in storage, but Ive never used it. I normally dont have that much problem..but for a few months every summer...
I live in the middle of the Oilfields..here in the desert...and the power does wierd and funny things depending on price of oil, how many ACs are running and so forth.
This was brought up once b4. IIRC the story was voltage started out at 110, went to 115, then went to 117 and is now at 120 to get more power through the exsisting wire network.
See my reply to gunner, my power company goes by +/- 5%
iiuc, even cheapy meters are calibrated to true rms. If your meter has a full-scale reading of 250 V, and is more than an inch wide, you proly got fair accuracy. I don't know that cheapy digital are any more accurate than cheapy analog, either.
You won't get the best accuracy measuring 240 V on a 1,000 V scale, altho this in fact may apply more to analog than digital.
120/208 Wye service is common in office and apartment buildings in the US, as you can run heavy appliances such as ovens, clothes dryers, air conditioners off the 208 (sometimes needs an autotransformer if they don't like 208 and require 230) and you get 120 V from line to neutral.
it is EXTREMELY, EXTREMELY uncommon in single-family residential communities. For instance, we have single-phase 7200 V distribution on my street, with the 7200 V 3-phase a block away. I know of two houses on my way to work that have 3-phase service. I can tell because they have 3 25 KVA pole pigs on their pole. These are BIIIIG houses, one was featured in the paper some years ago, and is 14000 sq ft. In many areas, the power company will flatly refuse to install 3-phase to a residence. I don't exactly know the reason for that, it may have to do with state utility tariff stuff and the requirement that 3-phase has peak demand metering and residential is net rate metering.
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