ECN Forum Forums General Topics of the Trade General Discussion Area Residential 3 Phase, Why / Why Not?

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?

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).]

Come on down to Fairfield county, CT. I could show you several houses with 1200 and even 1600 amp 3-phase service!

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.

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.

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.

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).]

It gets very tricky.


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.

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

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