Supplied Voltage -- 208 vs. 240

Awl --
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.
--
EA/Mr. PV'd



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Some of you may find this link, posted by Jules in that thread, very inneresting. Gary Lucas would proly fall over in a safety-induced paroxysm!
(http://en.wikipedia.org/wiki/Ring_circuit
--
EA


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On Wed, 28 Oct 2009 14:23:41 -0400, "Existential Angst"

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.
Thank You, Randy
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Randy wrote:

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.
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Randy wrote:

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.
Best, Steve
--


Regards,
Steve Saling
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wrote:

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
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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!
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On Thu, 29 Oct 2009 04:08:15 +0000 (UTC), David Lesher

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.
Gunner
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Gunner Asch wrote:

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.
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: :Gunner Asch wrote: :> :> 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% +/-" : : : 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.
The transformer will be happier if the primary sees the reduced voltage unless it has the extra iron needed to handle 250 volts without starting to get into the saturation region. In essence, you're making a voltage divider, but with transformer windings, not resistors.
| <-----------250V-------------> | | | | @ @ | | +-----+ +----------+ | +----| 12V |--+--| 240V |----+ +-----+ | +----------+ | | | | | | <----238.1V----> |
Mind the polarity dots. You're hooking this up in "boost" polarity, but then reversing the roles of input and output.
--
Bob Nichols AT comcast.net I am "RNichols42"

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Robert Nichols wrote:

So far I have never had a buck reansformer saturate, but I know how it works. :)
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: :Robert Nichols wrote: :> :> The transformer will be happier if the primary sees the reduced voltage :> unless it has the extra iron needed to handle 250 volts without starting :> to get into the saturation region. In essence, you're making a voltage :> divider, but with transformer windings, not resistors. :> :> :> | <-----------250V-------------> | :> | |
:> | +-----+ +----------+ | :> +----| 12V |--+--| 240V |----+ :> +-----+ | +----------+ | :> | | :> | | :> | <----238.1V----> | :> :> Mind the polarity dots. You're hooking this up in "boost" polarity, :> but then reversing the roles of input and output. : : : So far I have never had a buck reansformer saturate, but I know how :it works. :)
Have you ever hooked up a 'scope displaying the input current waveform on an unloaded transformer and seen how the current spikes up at the end of each half cycle? That's the core starting to go into saturation, and it doesn't take much overvoltage to cause it. Wherever possible, I prefer not to ask a transformer winding to handle more than its nominal voltage.
--
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Robert Nichols wrote:

Yes, i have That's how I know none of them were saturating. I've worked in electronics for almost 45 years. Repair, manufacturing & as a broadcast engineer.
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I just had 3 ph service connected to my residence where I have my shop. I have learned more that I want to know about AC power distribution. The power company quoted $1200 and one week after city inspection to connect to my new service entrance. It took 13 weeks to get it done. Seems like they failed to check the avalible space on the pole in my yard.
The primary 3ph on the pole is 7600V. I could have anything I wanted because the transformer(s) determine what you get. I chose delta 240V. The power company refers to transformers as pots. The single phase center tapped pot is connected like it would feed a single 240V service, thats neutral and one phase on the primary lines. Another pot is connected to neutral and another phase. The secondary is connected to the center tap (neutral secondary of the other pot) and creats the third phase from the other wire. It's open delta but if the power load demanded it another pot would be added to close the delta for more power. Safety ground comes from the service entrance ground rod and connects to the incoming neutral bus bar in the panel. The service entrance is the only place the neutral and safety ground can be connected. With a delta connection the neutral is taken from the center tap of one winding. That makes the third leg higher that the others from neutral. I think it's about 280V. It's referred to as the high leg and must be marked orange. It also must come into the panel as the middle conductor. No single phase power is taken from it. Wye connected power has 120V to neutral from all three legs but across the legs is 208V. It's used in offices where most of the power is 120V 1ph.
The original single phase service is connected to the house. The new service is connected to the shop and is on the two phases not connected to the house. Should the original secondary trip off I still have power. I don't share the 3ph pots so the only load is my load on the secondary side. I am 1/2 mile from the power station that supplies the primary from the distribution lines. The power plant one mile away and in sight of my shop. I rarely loose power.
Dave
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On Wed, 28 Oct 2009 19:57:19 -0700, Gunner Asch

P P & L (http://www.pplelectric.com/Commercial+and+Industrial /) states they supply power +/- 5% and 60 hz +/- 0.1hz
Thank You, Randy
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GD, My 240 3 phase has always been 245-247 & all my Fanuc controls have ran fine with that. OTC & OTD's.
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On Thu, 29 Oct 2009 02:19:27 -0500, why <why> wrote:

My voltage is right around there too. Cheapy meter, I don't have a truew RMS meter.
My Fanuc 0M-C runs fine with it.
Thank You, Randy
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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.
--
EA


>
> My Fanuc 0M-C runs fine with it.
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On Thu, 29 Oct 2009 11:30:13 -0400, "Existential Angst"

I don't own an analog meter any more. Thank You, Randy
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It's not a issue of regional geography; rather it's more influenced by street. Are you in a resi area, light office, or industrial?
208 results from 3 phase 120 p-n; it's a resi/maybe light offices. 240 usually comes from 480v found in industry.
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