3-phase vs 1-phase

[Hose B]

OK guys I think I'm getting somewhere. I told a bit about my situation in my intro. Here me out on this, because I dont want to misunderstand.

When I purchaced my home, my electrician told me I have 3-phase power. The meaning of this in my small brain was that if I have 3-phase - EVERYTHING in my house -outlets, light sockets and all - somehow are using 3-phase power. That probably sounds as goofy to you as it does to me now. Nonetheless, that is where my brain has been.

Now, I think I understand: I do indeed have 3-phase power available at my service panel, but unless I wire a circuit to the additional leg, my house uses single phase by default. In other words, single phase circuits use 3 conductors and 3-phase cuircuits use 4 conductors. Is this generally true?

I hope someone can tell me if I'm seeing the light. If I am correct, can someone explain the difference between single and 3-phase power in terms of what the current is doing and why 3-phase is "better" for motors.

Thanks again guys :confused:

[browny]

Your normal power/light circuits will just be connected to individual leg(s) of the three phase circuit.

Your entire house might run off only one of the three phases available, or they might have spread the circuits across the three (eg 6 circuits on red phase or 2 circuits red, 2 blue, 2 white).

3 phase is just about bigger more powerful equipment.

One thing I have noticed (in Aus) is that the 2nd hand market for the smaller 3 ph industrial gear can offer great bang for buck. eg I can buy twice the 3 phase machine for the same money as single phase

[MAC702]

Most homes (every one I know of) here in the USA are single-phase, meaning there are two hot legs (separated by 240V) with a neutral between them for your 120V. There is only ONE way to get power from a hot to a hot. With 3-phase, you have three hots and therefore THREE ways to go from any hot to any other hot (like a triangle). You will still also get a neutral (grounded conductor) for your 120V.

3-phase equipment allows a much higher density of power. Instead of a single sine wave that crosses zero many times, you will have essentially three sine waves that are in different phases, and you will always have a significant area under the curve (between at least two of the waves and the zero).

[David R]

Three phase is cheaper to run big stuff.

David

[MAC702]

That is the equation Power = Voltage * Current, which is certainly a good one to know, but it's not Ohm's Law.

Ohm's Law is Volts = Current * Resistance, V (or E) = I * R, etc.

The Power Company charges for power. They know the voltage they are supplying, and measure the current, yes, but they are billing you for power. Your choice of equipment and input voltages will not affect your bill at the end of the month.

[browny]

I agree. Electricity companies charge based on the energy used, not the current used.

[bruceb]

I have never seen 3 phase power brought into a house because it is not necessary unless you are running heavy duty equipment.

Do you have overhead wires coming to your house? How may conductors?

[Sober_Pollock]

It is HIGHLY unusual to have three phase in a residence. I've NEVER seen it done. A few farms I've been to, yes, But never a residence.

You should definitely verify this to be true before you spend any money on any three phase equipment.

Call your utility company to find out.

[smithboy]

We have a quite a few bigger houses that have three phase to run thier big ac systems. I live on the border between a residential and industrial use area and at least one house on our street has three phase power at the breaker panel, but I think they only have one three phase circuit running out of it to their central air. The rest are single phase...at least that what I was told. Unfortunately, this house is three houses down from me, and just a bit too far to go to simply get three phase to my shop...otherwise...

[awright]

My understanding is that utilities usually distribute 3 phase power all around the city on the high voltage lines on the power poles, but only tap off a single phase for low voltage distribution to a group of residences served by any single transformer. You will see one transformer serving several residences, and this is always a single phase transformer connected to only one phase of the three phases of the high voltage distribution system on the pole.

I can look out of my window from my computer and see a utility transformer with two high voltage insulator horns sticking up from the transformer case, indicating a single phase transformer, and I can see that it is connected to only two of the three identical high voltage wires running uppermost in the array of wires on the pole. Different phases are picked off to equalize the load on the 3 phases as determined by the utility engineers. If I walked down the street to the next transformer, keeping track of the three high voltage wires, I would probably see that the next transformer is connected to a different phase (put I am too lazy).

I believe that the primary reasons it is so expensive to get new 3-phase service to any arbitrary location in a non-industrial area is the cost of the probably under-utilized utility grade three phase transformer and metering required, in addition to possible extra costs of having a unique island of special service in a residential area with all single phase low voltage distribution. Additionally, of course, they have you by the short hairs.

Imagine the enthusiasm of the utility for providing a $10,000 utility transformer capable of serving a small factory, a $300 3 phase meter (or, at least, more than one meter - I don't know how 3 phases are metered), and labor for installation and wiring so you can run your drill press and welder in your basement a few times a month. Ain't gonna happen unless you compensate them for the initial cost, installation, and amortization of the equipment.

Are you sure you have 3 phase power to your service panel and not just to the utility power pole? It will be very easy to see the difference from single phase service. The easiest thing to observe is that you will have a 3 pole, rather than 2 pole main breaker and three insulated wires plus an uninsulated ground and carrier wire coming in, rather than two insulated and one uninsulated wire. The transformer on the utility pole serving your residence will also have three high voltage ceramic horn insulators sticking up from it, rather than the usual two, if it is a 3 phase transformer.

awright

[awright]

Oh, yeah. Hose B asked, " ...can someone explain the difference between single and 3-phase power in terms of what the current is doing and why 3-phase is "better" for motors."

Three phase is better for motors because (1) you get constant torque instead of 120 torque impulses per second out of the motor, (2) you can eliminate start windings, start capacitors, and start centrifugal switches from the motor, resulting in a cheaper and much more reliable motor, and (3) you normally can start a load with lower initial current draw from the lines.

You will notice that it is difficult to find a single phase motor of more than two or three horsepower and if you do find one, it is very expensive. That is because the starting hardware and current draw become impractically large.

Some of these advantages are lost when you, as a homeowner, resort to a phase converter or VFD (Variable Frequency Drive, also called VSD, Variable Speed Drive) to get your 3 phase power. However, being able to utilize used 3 phase equipment bought cheaply at auctions because most homeowners cannot use them is a tremendous advantage that makes up for the loss of other advantages. I LOVE the VFD I installed in my garage a couple of decades ago.

Explaining what the current is doing is a little complex for simple verbal description here and I never learned how to post figures. Try googling "3 phase" or checking out a book on electricity.

awright

[Sober_Pollock]

I my neighborhood, we don't have three phase "to the curb", or in other words on the pole in my back yard.....

A 7200 volt three phase line runs along the south edge of the subdivision three blocks away.....

They didn't run all three phases down each block, they ran phase "A" down the first street, phase "B" down the second street, and phase "C" down the third street. They continued to alternate it this way.....

Alternating by the block rather than by the house cuts down on the number of miles of conductor they need to run.....

This means the nearest three phase to me is three blocks away.....

I've never seen three phase in a residence. What part of Georgia is that? What's the name of the utility there?

I'd like to call them, I have some questions for them.

[383bigblock]

I'm in the process of building a shop in my back yard 30 x 36 and looked into 3phase power for equipment and they (TXU) said that they could do it but the cost was outrageous. They would have to bring in another Transformer and they would pass the cost on to me. I can buy quite a few phase converters or swap out motors for the additional cost. Strangley enough TXU appeared that they were willing to do it if I asked however the city was not willing to grant me the permit to do it. I never pushed because it wasn't worth the expense. I think there's more to it than just asking otherwise you would see it in the Residential areas.

Michael

[Hose B]

I've had a couple of electricians at my home for various services. They all have remarked at how unusual (but cool!) it is to see 3-phase service to a residence. I'm thankful for it with my AC in Phoenix! There are a number of poeple in this neighborhood in central Phoenix who have three-phase, albeit is very unusual. These homes were built in the 50's.

My main question is this: Must a 3-phase circuit have 3 conductors or 4? I'm trying to figure out if my welding outlet in my garage which has 3 conductors (2 hot and a ground, 240V) is 3-phase or single phase. Can you tell by just the number of conductors?

Thank you :confused:

[David R]

Its single phase. You need 3 hots and a ground for 3 phase.

David

[Hose B]

Its single phase. You need 3 hots and a ground for 3 phase.

David

Sweet. Despite my having 3-phase available at my breaker, my welding outlet is wired as decribed above. I wasnt sure if I could run my single phase welders off of that outlet. Now I know I can. Thank you!

:)

[Hose B]

There is obviously a LOT of know-how amongst the replies I've gotten from all of you. Just wanted to say thank you.

Now I'm going to fire up ol' red and strike an arc or two!

[all4naught]

The big cost savings in 3 phase power is not in how motors that use it are constructed or the the power densities in polyphase distribution. It is in the way the power company measures the power used and bills at commercial vs residential rates. The power company only bills a 3-phase customer for the unbalanced load that is returned to the power line. This is primarily because of the way the power company uses a control transformer on the neutral( in the case of Wye configured 3-phase) to determine power used. They usually don't place 3 control transformers (one on each leg) and feed it back to one meter. I have never seen a 3 phase meter that can totalize inputs from all three phases. Also since Joe homeowner doesn't need 3 phase normally 3 phase power is supplied at a lower commercial rate. With powerfactor correct equipment and phase balancing techniques you can use massive amounts of power for significantly less money. There are 3 types of 3-phase power distribution Wye,Delta and High Leg.

What you mean that factory down the street is only paying a fraction of the cost of residential customers? Seems like a subsidy doesn't it.

But I would like to see a picture of Hose B's panel or panels and meter base. I think he and his electrician are mistaken. I won't tell you what I'm looking for until he posts some pics (don't want to give it away). When you go above the normal 200A single phase service some power company's do things different and it only appears you have 3-phase.

[awright]

all4naught, you seem to be saying that a customer with a perfectly balanced load (say, a three phase resistively heated oven) would pay nothing for the power he uses. No way!

I think you are confusing the fact that it only takes two meters to accurately measure exactly all the power consumed by a 3 phase (delta) load with the issue of rate structures and modes of charging for power. Use of two meters is a straightforward matter of the physics of three phase power flow, not a matter of the utility only charging for an unbalanced portion of the customer's consumption. Rest assured that the power company charges for (or, at least, fully intends to charge for) ALL real power consumed by a customer, balanced or otherwise, and applies surcharges for reactive loading or excessively unbalanced loading that causes problems or extra expense for the utility.

Large energy consumers do, in fact, get special rates that residential customers would drool over, but this is a matter of competitive pricing, bargaining power of large power consumers, the utility trying to retain customers who may resort to co-generation if utility rates are not attractive, the economies of scale in delivery of large amounts of power, rate structure fights before the PUC, politics, etc., etc. Pretty much the same as a company buying a fleet of cars getting a much better price than Joe Blow coming into the salesroom off the street.

And, of course, the earlier discussion was not about factory three phase power costs vs. residential single phase power, it was about single phase vs. three phase power for a residential/home shop user.

awright

[browny]

Electricity companies in Aus definitely charge for the total amount of energy used by a 3 phase customer.

Our three phase power meters have a CT and voltage connection on each phase.

It would surprise me if the US was different and they are giving power away...

[enlpck]

There are a wide variety of styles of three phase meters, and selection is based on the service provided.

An open delta service will have two current paths and one or two potential inputs. A balanced or corner grounded delta will be the same two leg meter setup. A balanced wye (neutral not carried to the customer) will probably be a two leg feed meter, but may be a three leg, and unbalanced wye (neutral is carried) will be a three leg meter, as current can (and often will) flow through the neutral. A delta with a split (120/240) phase may be a two or a three leg meter... two leg if metered ahead of the transformers, three if metered after.

The service at one of my jobs is open delta, three leg meter. The meter has two (internal) voltage taps, as well. I am guessing that the error from differential load on the sides of the split phase is presumed to be less than the meter accuracy.

Other job is wye service with neutral, three leg meter with three voltage taps. Current transformers are used, and there is also unbalance metering. No power factor metering.

Setup before being upgraded 7 or 8 years ago was a seperate meter for each phase (volgade referenced back to the neutral) and no unbalance metering.


If you look at how the mechanical style meters are designed, it is fairly easy to 'read' the details of a particular meter, even if the data tag is obstructed. In the case above, I read the data tag :) The modern electronic meters are, in many way, a marvel, but they are much less magical than the mecanical jobs.

I had the pleasure many years ago of seeing an old chemical meter (long since unused, but never removed). Weigh the plates when inserted, weigh them again a month later, the change in weight tells you the amp-hours used. Only good for DC. Was in a substation used by NY transit.

[MAC702]

...The power company only bills a 3-phase customer for the unbalanced load that is returned to the power line...

...There are 3 types of 3-phase power distribution Wye,Delta and High Leg...

The first incorrect issue was addressed already.

The next statement I quoted is also incorrect, at least from the way I would use those terms. Wye and Delta are two types of 3-phase power distribution, yes. a "high leg" is an issue associated with a center-tapped (grounded) Delta. Or were you using the term to identify that particular type of Delta as opposed to a corner-grounded Delta?

[Hose B]

The big cost savings in 3 phase power is not in how motors that use it are constructed or the the power densities in polyphase distribution. It is in the way the power company measures the power used and bills at commercial vs residential rates. The power company only bills a 3-phase customer for the unbalanced load that is returned to the power line. This is primarily because of the way the power company uses a control transformer on the neutral( in the case of Wye configured 3-phase) to determine power used. They usually don't place 3 control transformers (one on each leg) and feed it back to one meter. I have never seen a 3 phase meter that can totalize inputs from all three phases. Also since Joe homeowner doesn't need 3 phase normally 3 phase power is supplied at a lower commercial rate. With powerfactor correct equipment and phase balancing techniques you can use massive amounts of power for significantly less money. There are 3 types of 3-phase power distribution Wye,Delta and High Leg.

What you mean that factory down the street is only paying a fraction of the cost of residential customers? Seems like a subsidy doesn't it.

But I would like to see a picture of Hose B's panel or panels and meter base. I think he and his electrician are mistaken. I won't tell you what I'm looking for until he posts some pics (don't want to give it away). When you go above the normal 200A single phase service some power company's do things different and it only appears you have 3-phase.


I still do not know whether I have a Wye or Delta or ??? type 3-phase service. Furthermore, it is beyound the scope of my use especially at my residence. I would leave it to someone who deals in power distribution to worry, and know about that. I am not an electrician.

I have learned a fair amount of theory, in school and know the difference between say, Ohm's law and the power equation; probably enough to get me in trouble...:laugh:

Anywho, here are some shots of my service, and, if you feel, from looking at these photos, that I dont have 3-phase service, please let me know.

BTW - the photos are all rotated to the right to keep the aspect correct. So right is "up". I look forward to hearing back! Thanks.

[slamdvw]

Looks like 3 phase to me, I'd venture to guess Delta. The orange wire gives me that indication. Measure between the ORANGE wire to Ground ( or neutral ) if it's 208, it's delta. Delta with a center tapped neutral.

Of course, I might be wrong about the type, but it is 3 phase nonetheless.

[awright]

Sure does look like three phase service to me. Can't read any labels, but it looks like a triple breaker between the incoming three wires and the three lug bars that the breakers mount to. Lucky guy.

It looks like you have a ganged triple breaker just above the main breaker. Does that feed another 3 phase panel somewhere or a 3 phase appliance? This panel doesn't look like it has as many single breakers for receptacles and lighting that one would expect in a modern home.

awright

[Sober_Pollock]

Looks Like Three Phase To Me Too.

If that box is right next to your meter, are they both outside?

[awright]

Actually, 69 chevy, your power equation P = (I^2) * R is perfectly good, as are P = E * I and P = (E^2)/R They are all identical when Ohm's law is taken into consideration. That is, the basic power equation P = E * I can be converted directly to P = (I^2) * R by substituting I * R for E, which is Ohm's law.

Power calculations do get more complicated when you are dealing with AC power and reactive loads like motors and transformers. However, for AC power applied to purely resistive loads, the three forms of the power equation above are directly applicable.

Your only error was believing that the utility charges for current instead of energy. Your power meter measures both voltage and current and automatically logs energy consumed.

awright

[Sandy]

There is a handy dandy little pocket book out there called "Ugly's Electrical References". For flunkies like me who just want to refer back to the basics once in a while it's great.

I won't get into the foray of what anyone thinks ohms law is but here is a snap shot of a wheel that a guy can make copies of and scatter all over the place.

Give all credit to the publishers of the pocket book.

I rotated it to try and maintain a decent graphic size and stay within the allowed size. You'll need to rotate it back.

[MAC702]

Looks like 3 phase to me, I'd venture to guess Delta. The orange wire gives me that indication. Measure between the ORANGE wire to Ground ( or neutral ) if it's 208, it's delta. Delta with a center tapped neutral.

Of course, I might be wrong about the type, but it is 3 phase nonetheless.
Yep, I agree. The orange is a good clue, but not conclusive. Only recent NEC's require the orange on the high leg, but it was common practice for many years. However, it is still permissible to use orange on any hot leg that is not associated with a center-grounded delta service, also.

Measure voltage on the orange leg to ground and let us know what you have. Are there any 120V breakers currently on the orange phase? If not, that's another big clue.

Now that we know for sure you have 3-phase service, what was the original question again? :)

[WolfmanJack13]

With the type of setup you have you will have 208 volts between any two of the three hots on the main breaker. Also you will have 120 volts between any hot and the nuetral wire.

[MAC702]

Wolfman, why do you assume it is a wye set-up? While it could still be either, the evidence actually points toward a delta. There are no 120V breakers on the 'C' phase, which is orange. If so, your advice would be very wrong.

Welcome to the forum, though! What are your electrical qualifications?

[WolfmanJack13]

I stand corrected in the fact that one should never assume(something I stress to all my apprentices). The nuetral elimanates standard delta or open delta. So that leaves wye or high leg delta. Without seeing transformer connections the only way to be positve is with a voltage tester from each phase to nuetral. Only wired two three phase houses in all my years. I've only seen high leg delta on commercial/industrial setups and not that many of those. Would be very dangerous to an unsuspecting home owner to have high leg delta. As for experience, I've been in the trade for 28 years, 20 proudly as an IBEW member woriking both in Canada and the US. Thanks for the welcome. What local do you hail from by the way?

[Hose B]

Sure does look like three phase service to me. Can't read any labels, but it looks like a triple breaker between the incoming three wires and the three lug bars that the breakers mount to. Lucky guy.

It looks like you have a ganged triple breaker just above the main breaker. Does that feed another 3 phase panel somewhere or a 3 phase appliance? This panel doesn't look like it has as many single breakers for receptacles and lighting that one would expect in a modern home.

awright

AWright - the triple gang goes to my air conditioner, the only appliance that I have that really benefits from having 3-phase.

I have a subpanel within my home that distributes lighting, etc. I should take a photo of that subpanel and show it to you guys because it is truly a work of art in wire management.

I still cant say I understand all of this about the different types of 3-phase you guys were discussing, but I have a learned a wealth of information just from you discussing it. Thanks!

Funny thing is this whole discussion arose from me thinking that if I had 3-phase service, that my entire house had 3-phase flavored power!:laugh: I wasnt sure if I could run my single phase Lincoln on a 240 oultlet that is in my garage. The key, I have learned, for something to be wired 3-phase is that it requires 4 conductors. My outlet has 3 conductors --> single phase.

Through this discussion I was asking for a mole hill answer and have been given a mountain's worth of information. I only hope that I can provide some answers for someone sometime. Thanks again! :cool:

[MAC702]

...I've only seen high leg delta on commercial/industrial setups and not that many of those. Would be very dangerous to an unsuspecting home owner to have high leg delta. As for experience, I've been in the trade for 28 years, 20 proudly as an IBEW member woriking both in Canada and the US. Thanks for the welcome. What local do you hail from by the way?
We are in Las Vegas #357. We've never seen 3-phase residential at all, and I've now helped with two over the Internet in the last two weeks. Weird. But the union does very little residential here. Las Vegas is also a new town. You won't find anything older than Zinsco around here, and that's rare, too.

I've designed several 3-phase Kingdom Halls for Jehovah's Witnesses, though. When you have two auditoriums, a lobby, a library, a conference room, and an apartment; the A/C load alone makes it worth it. But 120/208V Wye is still the way to go.

I agree that a 3-phase Delta is a bad idea for an unsuspecting homeowner. But 3-phase is very fortunate!! You can't even ask for it around here, even though the nearest pole with it might be 4 houses away.

[RonL]

Three Phase 208 wye for residences makes a lot of sense to me. Although it would be more expensive initially, the efficiency of the system would even the costs out. We would be better served if all motors larger than 120 volt fractional horsepower were three phase. As far as wiring a house is concerned, all 120 volt wiring would remain the same. All single phase 208 would be the same ( except for the fact that it would be 208 rather than 240). Three phase wiring would require four wire runs rather than three. This would be ameliorated somewhat by the fact that you could use lighter guage wire. If 208 wye became the norm, I think that refridgerators, air conditioners, and other motorized appliances would become three phase. Even welders would benefit. Three phase rectified transformer welders have a smoother arc.
In other parts of the world, three phase is more commonly used in residences and farms.

RonL

[MAC702]

I couldn't agree more.

[driftstar]

I'm so confused by this stuff... Electircal stuff isn't my strong point... but I can weld like mofo! :D LOL