I have a question,why not provide homes with 3 phase power? With energy conservation being a "hot subject" it seems to be a tremendous waste to have single phase air conditioning equipment in most of the new homes constructed.

One word: MONEY

From the POCO end: Extra transformers, 4-wire service drops, three-phase metering, and in a lot (most?) of the residential areas, lack of three-phase primarys. (And let's not get into the whole open-delta thing, please.)

From the homebuilder's end: Increased cost for the 3-phase panel and main breakers. Increased cost to wire up the appliances.

But it would be more efficient, agreed.

I suppose there might be a buck or two to save in a big McMansion but most houses would be better served by simply using better glass and more insulation. The new HVAC systems are really pretty efficient.
Other than pool pumps I doubt there is much else that would benefit from 3 phase.

In my home town (Oradell NJ) there's several late 50's houses fed with 3 phase power (normal 120/240 with an open delta 240v). Must have been the first houses with central air. Presumidly the homeowners have never mistaken the 208V line for 120V.

I was unaware that there is a big difference in efficiency between single-phase and three-phase air-conditioning equipment. Just how big is the difference?

In my 15 years, I have worked in exactly 1 residential home that had 3 phase power to it. The owner was filthy rich. All the HVAC equipment is also 3 phase, and even some kitchen appliances. The pool in the basement may also be powered by 3 phase equip but I'm not sure about that. Yes, a pool in the basement, nice, huh?

Latest technology for AirCon is to use dc motors & inverters to give infinitely variable compressors and evaporators and 'soft start'. Coupled with microprocessor control and ozone-friendly refrigerant, [R410A] these units easily achieve COPs of well over 4, so that the difference between 3 and single phase operation is nil.
www.toshiba-aircon.co.uk

[Link gives a good idea on wassappenin',
technology wise, I'm not saying they're better than others.]

Having seen neighbors juggling their demand between phases and continually tripping breakers when they plug their kettle into the 'wrong' recep., I'd say 3 phase and residential is a bad idea.

Alan



[This message has been edited by Alan Belson (edited 01-21-2006).]

3-phase domestic supplies are pretty common in Continental Europe, although not here in the U.K.

So many of those supplies are very low rated though, sometimes set for only 15 or 20A per phase. As Alan says, you have to juggle what to Americans and Brits seem like small loads just to avoid tripping a main breaker.

Somehow I can't imagine that being a problem if 3-phase were used in U.S. homes, as the services would be "a little" heftier.

Watts are watts regardless of them being delivered three phase or single phase.

746 watts per HP is unchanging.

Advantages of three phase are smaller conductors.

Disadvantages...cost.

Any three phase distribution equipment costs more than the equivalent single phase equipment.

We had one home on our system that had a true 3 phase service.
Someone had convinced this guy that 3 phase was cheaper than single phase. (Still haven't ever gotten a good explanation on why people think that .

Anyway, after living there a couple of years, he decided his bill was too high and had the entire house converted back to single phase. (More cost for no significant return).

This guy was singularly lacking in wit or tack, so the fun part was during the conversion when they installed the single phase equipment before we had changed out his delta bank. The AC guy hooked the controls up to the 208 high leg and fried the AC.

Of course, Mr. "I've got more dollars than sense" wanted us, the POCO, to pay for it.

We just smiled


[This message has been edited by WFO (edited 01-21-2006).]

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

Germany is such a country: Standard service per apartment / small house is 3 x 63A @ 400/230, i.e. 43,5 kW.

In the residential area there are just two devices always (mandatorily) running on 3phase: Ranges/cookers (usually 3 x 16 A or about 11kW, wire gauge 2,5mm2) and instant water heaters (correct word?) between 18 kw and 27kW, wire gauge usually 4 to 6 mm2. Use of both is rather common, just I haven't got none of them, because I'm cooking , drying and heating (also water) on gas(NG) actually.

AC is not very necessary (climate), therefore we're depending on models from other markets usually often running on 1 phase with expensive wiring due to uncommon loads.

I think you are pretty right that on small induction motors efficiency is not a real issue, but in the simplest industrial context , 3p becomes indispensable because of better efficiency and much better torque of motors.

The cost thing is not obvious at all. Here we use probably less copper to transport the energy. Prices for breakers and other equipment here are extremely depending on production numbers. A standard B16 A breaker is about 1 to 2 $. A K20 (same brand, same housing, only different electric values) needed maybe for an AC device can be at 20 $. I buy a standard 40A/30mA RCD (sort of GFI) for about 25$, a 63A/30mA RCD is already almost the double price. It means, 3p can become cheaper than 1p in case it is regarded as standard.

The result are rather slim panels. And the price is my work, not the material.

To a first order approximation, you can get multi-phase power from a single phase source with motor run capacitors. The cap shifts the phase 90 degrees. Such lash-ups are designed and built by the manufacturer of the equipment (fridges, air conditioners and such), and are not usually "visible" to the user in terms of the electrical hookup.

Technically, couldn't one have a circuit with a shared neutral and three conductors at 120V line to neutral?

Charles, you didn't specify the phase relationship you have in mind between the "three conductors" to neutral. If they are at 120 degrees, what you describe is exactly 208Y/120. If you're thinking of taking the three conductors from a single-phase source, then, no, it won't work.



[This message has been edited by SolarPowered (edited 01-22-2006).]

If you have a true 120/208V 4w wye service (equal to Continental European 230/400V) you can have a multiwire circuit with three phases instead of the US two. You'd need a 3-pole breaker, just like a US 1ph multi wire reuqires a double-pole. in Germany and Austria that practice is frowned upon though, out of fear of lost neutrals with the small wires (roughly 15 AWG) usually involved in house wiring.

There's one nice thing to 3ph though: imagine hooking up a range with 12-4 cable on a 20amp 3-pole breaker... in my opinion smaller wires are a lot nicer to work with, so I prefer the European 3ph arrangements, especially with the higher voltage levels involved current gets fairly low.

Of course French 15A services are ridiculously small. But I think 35A per phase @230V is quite enough for most uses. After all that more or less equals a US 100 amp service, along with the ability to run power-hungry appliances on 400V.

Recently I read about an average US single family home (an old farm somewhere in Maine) having to upgrade to a 600amp service for installing a heat pump and two or three tankless water heaters... from an Austrian point of view that's flat out ridiculous! Most electricians who do residential work aren't even trained to work on cables as big as that! I don't even want to think in metric what wire size would be required for 600amps!

SolarPowered;

Yes, sorry about that... I did mean 208Y/120. It sounds like a fairly neat idea, but has anyone seen it in practice? That is, 3 lines, sharing a neutral, 120 degrees out of phase with only 120V loads.

I mainly read these forums out of interest and curiousity, btw...

In the office environment it is common to find 3p wye serving 120v loads. That is why they invented "super neutral" cable.

Rewire.... would that be Silvestri's house on Rymal Road?

Yes it is!
Er Sandro, where are you????

Quote:
"Recently I read about an average US single family home (an old farm somewhere in Maine) having to upgrade to a 600amp service for installing a heat pump and two or three tankless water heaters... from an Austrian point of view that's flat out ridiculous! Most electricians who do residential work aren't even trained to work on cables as big as that! I don't even want to think in metric what wire size would be required for 600amps!"

We've got at least two homes on our system that have 150 Kva padmounts on them (single phase). One of them is on a "cash only" basis for payment.
I'm told that the Dell household in Austin (the Dell who owns Dell computers) has it's own substation.
The bigger the house, the more they complain about their bill.

As I understand with a single-phase shared neutral situation, anything that may show up on the neutral is effectively canceled out as one line is at +120V as the other is at -120V.

How much would a neutral have to handle on the three-phase set up, ratio wise?

Charles, if you were driving 3 heating elements of equal size (one per phase) the neutral current would be as close to zero as your match of elements.
As soon as you start using reactive loads those ugly harmonics raise their ugly head and neutral currents start adding. You can get neutral current that exceeds the phase.

I did a service call on a monumentally HUGE mansion (5 floors) off Mulholland Hwy in Hollywood Hills, built around the 1950's with a 3 phase 480V 1200A service. 3 elevators, enough A/C to have you singing "Oh Canada" in any weather, indoor pool, a jacuzzi on the roof, a computer mainframe room kept at about the same temp as your refrigerators salad drawer, and of all things, a bowling alley

Other than that, the Governator has a ranch in Malibu Hills with 3phase 1600A at 208Y/120V.
Those are the only 3 phase houses I've actually "worked" on.. But I have come across a handfull with 400A 240V 1 phase..

Seems most of the new houses in "The OC" are 200A 240V single phase.

So Cal Edison has load requirements which must be met before they will even consider giving you 3 phase power whether you're commercial or resi. If you don't draw enough Kw/H to meet this after they give you the 3 phase service, they'll charge you for a "minimum demand" anyways, which last I heard landed you in the $800/month ballpark

Wolfgang,


Although I still think 3-ph is an unnecessarily complex for domestic work, that's at least a decent supply rating, unlike some of the French ones.

That sounds very cheap. The cheapest single-phase B-type in my trade catalog is a GE at a little over $4 (same price for all ratings 6A through 40A).


Interesting comparisons with here, where 63A RCDs are very common. From the same GE range, and converted at £1 = $1.78:

30mA / 40A $35
30mA / 63A $45
30mA / 80A $61
Ragnar,

In metric sizes, about 400 sq. mm.

That would just about pay my electric bill for an entire year!

Just for better understanding:
the US "200A single phase service" = 200A @240V = 400A @120V = 48 kW? = about standard German service size

or only half of it?

Wolfgang (Europe)

What size 'choc-bloc' would 400mm2 require?

Alan

ps. Just dug out my biggest choc-bloc, bought for my new meter tails. Hole diameter 7mm, marked for use on 25mm2 conductors, 'Legrand', NF approved. They probably go bigger.

[This message has been edited by Alan Belson (edited 01-24-2006).]

[This message has been edited by Alan Belson (edited 01-24-2006).]

You will not get a LV service of 1 MW (1200A @3 x 480)here. You'll usually get your own xformer @ 11 or 20 KV. This gives you acceptable cable sizes, just needing a bit more equipment.

Great! Then you can always look forward to something like this:
https://www.electrical-contractor.net/ubb/Forum5/HTML/001115.html

...happening in your very own back yard!!

Of course, in my case the biggest problem the POCO would have is keeping me out of the SCADA system!! I love to watch air break switches in action!

A 200-amp service means you can draw up to 200A on each "hot" leg of the 3-wire supply, so 200A x 240V = 48kW.

That's double the power of the typical modern British service of 100A / 24kW (although ours are only 2-wire with everything running on 240V, of course).

Quote:
"Of course, in my case the biggest problem the POCO would have is keeping me out of the SCADA system!! I love to watch air break switches in action! "

Which is exactly why I've never let our company's SCADA system get incorporated into the company LAN.

In all seriousness, I hope you would never let an "urge" endanger a linemans' life.

Oops, I hit a landmine with that one. Let me clarify that to mean in the context of it being a substation serving ONLY my own house, like the Dell dudes'.

Some years ago in the Air Force I took the lineman's CDC (Career Developement Course) and exams to see how I'd fare. Passed with score of 86.

I had actually considered becoming a lineman, but I didn't because I can't stand heights. (Makes climbing and bucket work impractical.)

Working around high voltage doesn't really bother me (I did make contact with a live 12kv padmount switch, wearing all appropriate PPE thanks to a really cool foreman I knew), and have a facination with power equipment in general. I told the foreman, half-joking, that if I came upon a transformer fire, I'd probably bring out the hot dogs and 'smores.

Seriously, I've also been too close to some rather violent equipment failures to actually try such a thing. My very first encounter was when a pole-mount tx got hit by lightning as I rode by on my bicycle. My friend and I both got knocked on our little butts and had nightmares for weeks. I was around 7.