single phase vs. 3 phase

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Look at the main breaker in your distribution panel. If it has two handles tied together then you gave 220v single phase. If there are three , then you have 3 phase. If it is a residential installation, I doubt you have 3-phase power.
-- Al Reid
"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." --- Mark Twain

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I looked into 3 phase too, back when I was working for a company that regularly tossed 3p motors in the trash. I did have 3 phase primaries on the street. What I *might* have been able to get was 3p center tapped delta, 240 between phases, (2) 120v phases and a wild leg (208 to ground). It only required one extra transformer. It was still going to be expensive. I would need to install a 3p service disconnect, rewire my current panel as a sub and install another 3p sub. By the time I paid for the upgrade from the utility and upgraded my service I figured I could buy a lifetime supply of single phase motors so I passed. Where I live now I only have a single phase primary on the street so 3p is pretty much out of the question. There are tricks with capacitors that allow you to run 3p motors on single phase but the lack of efficiency in this trick negates any saving a 3p motor could get you. It might be a solution if you are getting the 3p equipment virtually for free and you don't use it a lot.
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snipped-for-privacy@aol.comGreg (Gfretwell) writes:

Would this type of service even work for three phase equipment?
The reason I want to do this is for big equipment like wide belt sanders and big planers. Ever try finding a used wide belt sander in single phase? I've got a better chance at the lottery. Three phase sanders are a dime a dozen. You can get new wide belt sanders in 10HP single phase, but only 25" and the cost is about $8,000.
The 20" Jet/Powermatic taiwanese planer for $2000 that is single phase is just junk compared to a used Powermatic. For $2,000 I could easily find an 18" or 20" old Powermatic with a three phase motor.
Very rarely you will see a Powermatic planer with single phase motor but the owners price them sky high because they know how rare the single phase beasts are.
Brian Elfert
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Brian Elfert wrote:

You state that the reason it the need for "big" equipment that has the advantage of being cheaper up front (purchase price) compared to (lesser quality) single phase equipment. I'm not sure of your intended use (production vs. sporadic home type use), but in general the most cost effective way to take advantage of the "cheaper" three phase equipment is with phase convertors. As stated before you do lose all the efficiency gains of true three phase but if the equipment is only actually running for a tiny fraction of the day these savings are invisible. Several neighbors have 5-7hp lathes and mills in their garages that they power with rotary convertors (made from a spare three phase motor) that work just fine. These things are only used for short times and the price of a surplus three phase lathe is far cheaper than any equivalent 1 phase tool.
If I was planning on what you are intending, I'd just get the 3-phase equipment and live with a phase convertor. Should the need arise later for true three phase, you probably can get it installed if the service is near by for several thousand dollars. -Bruce
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As long as the equipment is capable of being wired for 240v 3p (most do) it won't know about the center tap. The center tap is only used for the 120v loads. This arrangement also gives you the 240v single phase the other equipment in your house expects. It was what the utility advised but they weren't anxious to do it. It came down to money in the end. I could have got an upgrade to 400a 1p for free but the 3p was just called "expensive" by the engineer at PEPCO and neither of us pursued it farther. I didn't actually go to the sales office for how expensive it would be. Of course you also have to add the price of the service disconnect, main panel rewiring and the extra 3p panel. You might actually be able to get by with the capacitor trick (I think it is 4mfd per HP if memory serves) although a commercial phase converter is the better solution. I did get a 3p 3/4hp (3330 disk drive) motor spinning with a 3mfd capacitor but I never really used it for anything.
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Gfretwell wrote:

That's what I did on my 3 hp 3 phase milling machine, but it wasn't nearly free :) So far I have not noticed any drawbacks to the simple cheap way. If I was running the machine at full capacity in a commercial environment I probably would.
On my 3 hp 3 phase lathe, I got a VFD because I wanted variable speed control. Then I found out how nice they are for controlled rate stopping and starting and a bunch of other things. I would even use one on a metalworking lathe if I had three phase power. I probably wouldn't bother with a VFD on wood working tools, although it would be tempting if I got a ww lathe for turning large diameter items.
Rico
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Gfretwell wrote...

You missed out.
You could have used one of the three-phase motors as an "idler motor" to generate the third phase. Then, by adding capacitance to balance the inter-phase voltages and power factor for your typical loads, you could have used this "rotary converter" to power your three-phase equipment at full capacity.
Jim
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Might not help. Some main breakers are a one molded-one piece affair. Not easy to tell the difference by just looking at it. On the other hand there should be some printing on the breaker that will tell the difference. Greg
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The easy way is to _count_the_wires_ tied to the master breaker. this works *regardless* of whether it's a "molded one-piece affair", or not.
<grin>
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Count the wires up to your pole.

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look at the number of lines coming from your transformer into your shop. 3 lines = 3 phase, 2 lines = 1 phase.

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Maybe. I've got 3 wires coming to my house. It's 240V single phase. There's two hot legs plus a neutral. On the overhead drop from the pole on the street, the neutral is bare, but once it goes into a conduit down the side of the house to the meter and panel box, all three are insulated.
This is dangerous stuff to be guessing about. If you're not sure, the best thing to do is call an electrician. He'll be able to tell you what you've got in about 30 seconds by looking at it. Might cost you a few bucks for his time, but it beats burning your house down.
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The number of INSULATED lins ... There is also a neutral that is typically uninsulated. Total is 4 wires for 3p, 3 wires for 1p (in the US).
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Gfretwell wrote:

Neutral is typically (always?) insulated in a single phase system. Single phase = 3 insulated wires plus uninsulated ground.
Rico
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the neutral at my address is uninsulated. So it isn't always insulated.
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On Fri, 24 Oct 2003 14:15:46 -0500, Lazarus Long

Stop it ! You're scaring the Europeans 8-)
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On Fri, 24 Oct 2003 23:06:16 +0100, Andy Dingley

What? This isn't common? It's that way on all the houses I can see around here. Nobody's place is going up in flames, at least not because of anything the power companies doing.
How's it done in Europe?
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On Fri, 24 Oct 2003 22:59:04 -0500, Lazarus Long

We do bind our earths (grounds) to our neutrals, but we only do it at our substations, not at each premises (actually there are earthing systems where this is done, but it's not the usual way). So it's accepted that neutral may well be at some considerable potential w.r. to earth (depending on soil conditions) and thus should be insulated.
We generally regard electricity supply as a "3 wire" deal, where the electricity company feed offers live, neutral and earth as a package, and they're all treated separately inside the premises.
-- Die Gotterspammerung - Junkmail of the Gods
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On Sat, 25 Oct 2003 12:06:26 +0100, Andy Dingley

Crikey, it sounds like yet another Lucas scheme to badly ground the world. I'll bet you can see 50v floating grounds in that system.

So measuring each wire to earth, you get 220v on the live and zero on the neutral? Here, we measure 120v from each of the lives to ground, and 240v across them.
Here, we have two lives and a ground. Neutrals appear in the house as feedbacks to ground. The two lives are carried through the house singularly as 120v lives and the neutrals run back to the service panel (you might call that the mains box or something similar) and are tied to the same bar as ground. Grounding rods are at the telephone poles (old style) and at each house (newer).
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wrote:

We have a similar system to that for on-site work.
50V is "safe". It must be safe, because that's what the telephone system runs on, which is owned by the post office, so it would cost The Man a bunch of money to insulate. So 50V is regarded as the borderline between "compleely safe" and "instantly lethal".
On-site, we use 240V -> 110V isolation transformers, centre-tapped and earthed. So there's never any more than 55V earth difference on either leg, thus the tool is safe for on-site work.
-- Die Gotterspammerung - Junkmail of the Gods
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