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Joined: Jan 2006
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I would like that idea if my place were the "Palace of the electric motor".. OR it was a big place... ( In my dreams) .. There is one such house not far from here that requires 120 / 208 three phase because its that big... 18 car garage to start need I say more?
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Joined: May 2003
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Many larger Apt. buildings (Some of which I have done) have 3 phase 208 wye as a service for mixed commercial/residential, or even all residential if large enough. But the resi units only get two of three phases at the panels. All common areas and commercial units get 3 phase. A guide to rules for such are at the last 2 pages of this doc. PGE doc Edited to shrink page [This message has been edited by Roger (edited 01-21-2006).]
Mark Heller "Well - I oughta....." -Jackie Gleason
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Joined: Jan 2004
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Come on down to Fairfield county, CT. I could show you several houses with 1200 and even 1600 amp 3-phase service!
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Joined: Jul 2001
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Bob,
1HP mechanical output = 746W mechanical output.
You need to account for the effciency when converting from mechanical output to electrical input watts.
Many people mis-interpret the smaller ampacity requirements of a 3-phase motors as meaning they consume less power. The real cost savings of 3-phase is in the reduced "size" of the distribution system components.
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You need to account for the efficiency when converting from mechanical output to electrical input watts. Yes and this applies to single phase as well as 3 phase. You can by high efficiency motors or cheap ones. My point was the same as your point that going three phase does not necessarily mean energy savings any more than a 480 motor saves over the same HP (and efficiency) motor in 208 volt.
Bob Badger Construction & Maintenance Electrician Massachusetts
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Joined: Aug 2001
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Of course, Mr. "I've got more dollars than sense" wanted us, the POCO, to pay for it. Hmm..... The PoCo provided the 3-ph supply he asked for, then it's supposedly their fault when the A/C guy doesn't bother to check and find out that's it's a high-leg arrangement. I'm sure the judge would go for that argument.
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I agree that motor efficiency must be taken into account for 3 phase versus single phase.
Here is a quote from Reliance's web site on motor efficiency:
THREE PHASE POWER & SINGLE PHASE POWER 3 phase power is typically 150% more efficient than single phase in the same power range. In a single phase unit the power falls to zero three times during each cycle, in 3 phase it never drops to zero. The power delivered to the load is the same at any instant.
[This message has been edited by sandpiper (edited 01-22-2006).]
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It gets very tricky. In a single phase unit the power falls to zero three times during each cycle, in 3 phase it never drops to zero. Wouldn't that be 2 times per cycle? Regardless you are not paying for electricity when it falls to zero. A 5 HP motor provides 5 HP single or 3 phase. What you do notice is a significant size difference between a 5 HP single and a 5 HP 3 phase.
Bob Badger Construction & Maintenance Electrician Massachusetts
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We are comparing single-phase and three-phase induction motors, of course, not brush motors. Once running, the operating efficiency between the two types of ind. motor is of little actual significance to a home user, as you can't 'save on wire' if you use a single phase + a neutral at the point of use, and how many domestic three-phase food blenders, wash machines, hair driers, dish-washers, 'fridges etc. are on the market? The question was '3ph for domestic use' and all in all I still can't see any valid reason for it. If you want to save a few $$$s on a bit of wire, buy 230v kit and have done with it. Actually, I'd bet that dc-inverter brushless motors [no commutator; a permanent magnet armature; a chip and solid state switching to the field windings ] will sweep all these 'ancient' motors away in the next few years, for their starting torque, efficiency, small size and variable speed qualities.
Alan
Wood work but can't!
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Joined: Sep 2003
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THREE PHASE POWER & SINGLE PHASE POWER 3 phase power is typically 150% more efficient than single phase in the same power range. In a single phase unit the power falls to zero three times during each cycle, in 3 phase it never drops to zero. The power delivered to the load is the same at any instant.
If you have an 80% efficient single phase motor, there is no way that you will be able to replace it with a three phase motor that is 150% more efficient. -Jon
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