3-ph can be brought in using 3 wires (delta connected) or 4 wires (Y connected). The 4th wire is 'neutral' and separate from ground.

A generator should not be a problem unless you're talking about a whole-house generator, in which case you'll probably need a 3phase unit rather than split phase.

As to the solar system, I'm not aware offhand of anyone who makes a 3-ph invertor. I suppose you could just get 3 invertors and connect them to each phase, each with a part of the solar panel bank.

Does the home only have 1 meter? Or two? My folks have 3 phase in their home built in the 30s. It used to be farm house. The 3ph serves the AC only at this point. They have two meters for both service panels.

Would the original poster please tell us the voltage of the 3-phase system? This a test question before I expend more effort on this thread.

As a follow-up, one thing that I should have included, specifically, in my question was that by "complicated" I include "more expensive". If I decide to install a big generator and want 3-phase, will it cost more?

I looks like I may have run into more complicated with the solar already. One would think that industrial concerns must be installing equipment for 3-phase systems already. The cost might be higher due to economies of scale for inverter manufacture.

As for a transfer switch, I did consider that it is probably not more complicated at all for 120 single-phase circuits as they can be pulled over to a transfer switch the same as their counterparts in any service panel in the neighborhood. Anything that runs on 240 would require the same care as working with any other circuit in the panels.

Dont forget about the bundled grounds. Should they be called bundled or bungled?

I meant to include the following paragraph on my first Sunday post. Does this answer your question bus_driver?

Thanks for your quick response, weedmeister. There is a neutral and definitely one meter. I am assuming that there is a high/red/wild/ leg to get 240. I should have checked but I forgot. I may call the power company on Monday to confirm that.

"I am assuming that there is a high/red/wild/ leg to get 240."

The high ('wild')leg will not be 240 V but 208 V.

If you want to stay there a long time, consider putting in a dry transformer to provide 120/240 V.

They are actually common in commercial use since 3-phase is only needed for rotating machinery, and not for lighting or general use receptacles.

While the 'back rooms' may make use of 3-phase, the front office is 120 V, and in a home having regular 120/240 V is useful.

3-phase equipment tends to be significantly more expensive (even though the motors are cheaper to make) since it is often larger and has a more limited market.

For heating appliances 208 V in place of 240 V results in a loss of output power of around 25%.

Of course, brickeye, you are correct. The way the transformer is taped makes it possible to get 240, but not from that leg.

Why would I consider a dry transformer? I should already have 120/240 as well as 208?

Has anyone thought about the way the ground wires are done?

Basically, you have 208V line to line on the 3ph, and 120v line to neutral. All your single phase circuits are line-to-neutral. You don't have 240v anywhere. Now, if you look around, you'll probably notice that most 220/240v appliances are also rated at 208v.

The garage was probably done in anticipation of getting some 3-ph motor driven equipment (drill press, bench saw, etc) or welders.

Is it possible that the grounds for the single phase circuits were tied together with a pigtail to the busbar? Or that they were then tied to the box (same as the bar)?

I saw a solar installation on TV the other day. I thought the guy had a lot of invertors, and the narrator stated that it was a 19kw system. I'm assuming this owner split his solar arrays between the invertors since they all looked to be in the 3kw range. The fixed placement on his roof meant that not all the panels were getting direct sunlight at the same time.

I did a quick search and spotted a 4.6kw 208v 3ph invertor for around $2600, so they do exist in residential sizes.

Thanks, I deal with decisions about 208/240 equipment in the lab periodically. This is equipment with motors so I stay away from it as much as I can. They have voltage-boosting circuits so when running them on 208 power, they can not adjust for brown-outs as well as similar models that are designed for 120. The latter have voltage boosters as well.

Even without checking with the POCo, I am reasonably certain that I can get 240 out of this system since it is probably a "typical" residential three-phase system. I meant to check the outlet for the dryer. In addition to the dryer, resistance-heated appliances include, a cook top, oven, and water heater. There are lots of baseboard heaters around that are probably not really needed since there is central heat and not much heat is needed here. Some of them work and some do not. I don't know if they are 120V or higher.

I think that the bundled grounds are tied to the box. Thanks for the research on the inverter. Did you notice if it was designed for batteries or for net metering? As soon as I get some time, I will look around a little myself.

Reading the posts, I do not believe that ionized is at all nearly prepared to tackle this system at this time. Get a pro.

>assuming that there is a high/red/wild/ leg

While this is likely, it is by no means certain until you check with a voltmeter. Don't make too many plans yet.

bus_driver, what do you mean by "tackle"? I understand that no one here can tell me how to make changes in a home electrical system without looking at what I have installed. I know that I am neither qualified to make the evaluation, nor to make changes after someone else evaluates them. My skill set will enable me to do more in the improving drainage, painting, fixing, floors, foundations, alarm systems, and the myriad of other things that an old home needs than actually poking around in electrical service panels.

I remember the home fora at Gardenweb as didactic and advisory "places". So far, that looks to be true today. Could we get back to basics? What I would like to know is will a three-phase power supply make installing generator, via a transfer switch, or installing photovoltaic power more complicated (read expensive). In addition, I am interested in experienced opinions about why an electrician might bundle a bunch of ground wires together in a service panel or sub panel instead of hooking them to a ground bar.

In addition to those questions, I have a great need to understand how things work. That is why, when I bought a house 6 years ago (same power company) and was told by the inspector that it had three-phase power, I looked into it. It turned out that it had been converted to single-phase sometime after the original, 1950, three-phase AC compressor was replaced with single phase.

I called the power company this morning and asked to talk with their technical staff. A nice woman called back to arrange a meet with an engineer at the property and said that it is "120/240" service in their computer records. At this point I think it is pretty safe to assume it is 4 wire delta 120 / 240 V. That would mean that I can get single phase 12, single phase 240 and three-phase. That would be unlike the power I have available at work where 208 is the best I can get without the buck-boost transformers making up the difference which is a situation that I normally try to avoid.

Now, to answer bus_drivers question directly, I cant say that I know the "voltage" of the three-phase system in question for sure. I did not have a voltmeter with me last week. There are 4 wires in the drop and three main breakers in one panel.

In thinking about the future of this house, I will, in consultation with an electrician or two, have to make some decisions about whether it will be less expensive to keep the three-phase or remove the existing panels and meter and ask the power company for more conventional residential power. The house has a great, unobstructed South-facing roof. With current photovoltaic solar subsidies, I have to consider it. The cost might be prohibitive if the existing system does not lend itself to this kind of modification. The backup generator is something that I really want to do. Aspects of our lifestyle means that I would like to have a freezer full of things that my wife and I have put a lot of time into cooking. We have lots of potential for extended power outages here and I need a fighting chance to keep the freezer going in our absence.

Thanks

"At this point I think it is pretty safe to assume it is 4 wire delta 120 / 240 V."

Cannot be.

In 3-phase systems the voltages are given line-to-neutral, followed by line-to-line.

The relationship between the number is line-to-line = SQRT(3) * line-to-neutral.

If you have 120 V line-to-neutral (and a delta system does not actually have a neutral) the line-to-line voltage is 208 V.

120/240 V is an Edison system, not a 3-phase system.
Edison systems are 3 wire, but single phase.

If you looked at both hot wires on an oscilloscope they are 180 degrees apart.
This makes the peak 120 Vrms, -120 Vrms, each relative to a neutral defined as 0 Vrms.

It is possible to have a 240/416 V 3-phase delta system that has one of the 3-phases coupled as Edison circuits to produce 120/240 V. The center of one phase is then at 0 V.
This is the system that produces the 208 V 'wild leg'.

It is created from 120 V + 240 V of another phase (they add as vectors so (120 @0 degrees + 240 @120 degrees = 208 @ 90 degrees) relative to the neutral in the middle of the 120/240 V on one phase.

You probably should stop relying on the POCO (they may have an old or wrong record) and just go measure the voltages you have at the panel.

"What I would like to know is will a three-phase power supply make installing generator, via a transfer switch, or installing photovoltaic power more complicated (read expensive)."

It will be significantly more expensive.
Even a generator will cost more if you really have 3-phase.
They are larger and more complicated.
3-phase generators are most often 'commercial' sized to run large installations.
There is not any real market for a smaller 3-phase generator siunce 3-phase is normally not present in smaller residential settings.

"In addition, I am interested in experienced opinions about why an electrician might bundle a bunch of ground wires together in a service panel or sub panel instead of hooking them to a ground bar."

Sounds like a bad shortcut to avoid purchasing an additional ground bar.

>>"In addition, I am interested in experienced opinions about why an electrician might bundle a bunch of ground wires together in a service panel or sub panel instead of hooking them to a ground bar."

this is a common short cut, you'll see it all the time, and doesn't harm anything.

>>'There are 4 wires in the drop and three main breakers in one panel.'

this is likely a 3 phase wye supply, 120/208 v. not common in residential, but the property may be zoned commercial/residential if a previous owner had a shop on site. this is not a delta supply. if you want, you can follow the quadplex back to 3 individual can type transformers probably mounted on a near-by pole. note that in this configuration, there is 1 common point (neutral), and 3 other wires, 1 from each can, which are the insulated (208V) conductors. this gives you 120 from each 'hot' to the neutral, and also from ground, and 208 phase to phase or from hot to hot.

rick

Brickeye, thanks for the patient explanation. I have been looking at transformer diagrams and the waveforms in graphical depictions. Your explanation adds a lot to that.

In response to "Cannot be", that is what the power company calls it. As you said, I probably should stop relying on them. I guess I wont. With the information that I have now, I am better prepared to deal with anything that they might provide.

I spoke with two electricians today, a former neighbor and my FIL's neighbor that I will probably talk with some more as he was in a noisy place and it was inconvenient. (I still have one more I can call for a third opinion if I feel the need. He has a lot of high-voltage experience with a local institution and did some real nice work at my Katrina-ed house.) In addition, I called a local solar installer. It looks like I have my choice of generators if I dont want to run anything three-phase with it. If I want three-phase, and resistive heating appliances, it gets just slightly more complicated. Since BOTH of those seem unlikely, I think I am good to go.

As far as solar goes, the guy told me that it does not really matter what kind of power I have. I can net-meter with single-phase power on a three-phase service. I know that the only way I will really find out is to ask an installer to make a plan for me, but they guy seemed to grasp the problem and know what he was talking about.

Aspen31, youve just thrown a big monkey wrench into my machine! The area is strictly residential, though a smallish school nearby was recently torn down. It was active until near its end. There is so much resistive heating stuff in the house, I have a hard time believing that they would settle for 208 V max.

Someone is pulling your leg ionized and it ain't us. If you've got 120V outlets, there is no configuration of three phase other than another transformer that will give you 240. Just can't happen. They make grid tie inverters that will work in your situation, but you need to get ones that can handle three phase. That narrows your selection down considerably on the small end, but SMA makes them as well as others.

It is quite likely he has high-leg delta, which will provide single-phase at whatever the power company set the taps for, and could very well be 120/240 or it could be a little different. The high leg with the other two hots would then make a delta 3-phase 240.

If it is high-leg, then the breaker panel should have only 2 out of every 3 slots used for single-phase loads, plus a triple breaker for any 3-phase delta-connected loads. The high leg (the missing breakers) to neutral would be 208 and not a particularly useful connection.

But this is all useless speculation until some voltmeter readings are available.

Thanks, billhart. I did notice the missing breakers pattern. The only thing that I disagree with is that this is useless speculation. Though we are here to get and give useful help, I would be surprised if most of us dont agree that we would not be here if it was not is a fun and entertaining pastime, dont you agree? If this deal goes through, I will report back my findings. I am wondering if I will find anything else exotic there. I dont know whether to hope I dont or I do, but I will be keeping my eyes open for three-wire circuits.

I am still counting on the idea that there would be nothing really exotic installed here since it is, after all, a home. The only other news is that the power company engineer called this morning. He said that it is "120/240 open delta". It seems like a lot of the problem in describing this is with non-standardized nomenclature. I asked him, just to be sure, if I get real 240 out of that to run the kitchen appliances, dryer and water heater. His answer was yes.

This might just what I need to make the best choice of the options available for induction cooking! I have been wanting to explore that for some time.

I found some resources that some of you might find useful and others will yawn:

http://www.entergy-louisiana.com/Global/Your_Business/installation_standards/2008/OverheadSelfContained.pdf

http://en.wikipedia.org/wiki/High_leg_delta

Open delta is a way of supplying what is otherwise called high-leg delta or wild-leg delta. The difference is that they only use two transformers, leaving out one of the 3 that would be used in the delta for an industrial installation.

The voltages you get are the same, and you don't see any difference at your end except that the max load capacity is thus reduced, and the behavior of harmonic frequencies (multiples of 60 Hz) will be different if your loads generate a lot of them. Don't put a multi-KW load of industrial fluorescent lights or electronics on it and you'll be fine.

Well, billhart, that is interesting. I just poked around a very little bit. I am sure what you say is true. What is beginning to worry me just a little is that maybe if individual legs or neutral are lost on either (my or the power company's) side of the transformers that very bad things might happen to stuff in my house due to what the voltage do on the remaining legs. I don't have a good feel for that yet.

The risks aren't particularly worse than losing the neutral in a conventional 120/240 single phase system.

That reminds me of one of the worst electrical messes I ever saw:

There was a badly wired setup on a farm where the high leg had been added later, and given its own separate 1-pole disconnect switch (a violation of NEC requirement for 3-phase loads to have a 3-pole switch). If you shut off the original 120/240 disconnect before the high-leg disconnect, while a 3-phase motor was running, the high leg came back through the motor into the other two legs and the 208V fried small 120V appliances in the house.

I was at the place to look at a standby generator with 208 Y cranked up to 240V Y, and puzzling out if the difference between that and the high-leg service was a problem.

(end of relevance to this thread, but it is a good war story so I continue).

It turned out their biggest problem was the diesel engine had no tachometer but just a vibrating reed frequency meter on the generator. We figured out that they had run it at 40 Hz with the vibration harmonics weakly tickling the 60 Hz reed so they thought it was on speed. When we put a real frequency meter on it and cranked it up to 60 Hz, they said they had never heard it run that loud or seen the reed vibrate that much. Of course the electric motors hadn't lasted long on 40 Hz.

The diesel had all of its safeties (overspeed, low oil pressure, overtemperature, etc) broken or disabled. The exhaust pipe didn't quite get the fumes out of the building, and the muffler was bad so you needed earplugs to get within a stone's throw of it.

That place had a number of other problems, including a voltmeter with switches that could let it read each of the leg voltages. The switches were wired with #14 tapped right off the 400A fuses and the other side of the switches were bussed together and to the meter. It made a heck of a mess when two switches got pushed at the same time and thus shorted between hot legs. Need I add that the 400A fuses didn't notice when the switches vaporized.

Then there was the rat skeleton inside the generator control box, right next to the hole in the insulation he had been chewing on.

Or the many colors of fuzzy coatings that electrical connections can form when exposed to the humidity and ammonia produced by 10's of thousands of confined chickens.

The buildings are no longer there.

Billhart, as I read the last three sentences of your post, I thought that it might make a very nice Haiku.

Regarding the grounds being twisted together - there was another thread about that subject going on here before my last little jail visit, but I've been away long enough that my forum-searching skills have temporarily atrophied, and I cannot seem to find it.

It seems that one person was arguing that the only requirement was that all of the grounds be connected to one another and bonded to the panel, so he could get away with twisting all of them together and then just attaching one of them, instead of having a bus bar. Of course someone else was arguing that this was NOT acceptable, and I don't honestly recall what the final outcome was.

I gotta be honest, I did it on a couple of the first several subpanels I ever installed. I don't have an electrical-theory-based or operational-safety-related opposition to it, but it does seem to me to be, at the very least, "bad practice", if not illegal, and I don't do it anymore.

Regarding three-phase voltages... I haven't done much three-phase myself, and what little I did have contact with was 120Y208 and 277Y480 in the prison kitchen. That said, I have read a ton of theory and it's not foreign to me. I think I'm qualified to discuss it, and I shall do so.

It seems to me that, if we take that 240/416 (and thus 280 wild) configuration, and simply center-tap the 240, calling the tap "neutral", we've gotten 120, 208, 240, AND 416 out of it, simultaneously. If I were trying to advise some homeowner who had this system in place and who simply wanted to know if (s)he could get the normal residential voltages from it, I might be tempted to call it a "120/240 delta" system myself. There are also four wires (two ends and a center-tap [neutral], plus the wild leg), so I could very well call it a "4-wire delta 120/240" - so, brickeyee, I contest. I believe there CAN be such a thing, and I believe that's what ionized has here.

And as for the extra disconnected wire in the garage subpanel: I'll bet that said panel has 120/240 loads, and there is obviously no need for the wild leg to be hooked up.

Thinking back, I lied. I HAVE experienced this system before - I just didn't know what it was. My friend's grandfather bought an old dairy farm building, converting half of it into his house and the other into an auto body shop. Various aspects of his system (missing breaker pattern in some panels, different bus configurations in various subpanels, odd voltage measurements that didn't make sense to me at the time) sound strikingly similar to this thread. That place is right around the corner from where I live now (three corners, actually, if you're counting but it's still in the neighborhood), and I believe the same person still owns it. I wonder if he'd let me have a look now that I know what the heck it might be . . .

"It seems to me that, if we take that 240/416 (and thus 280 wild) configuration, and simply center-tap the 240, calling the tap "neutral", we've gotten 120, 208, 240, AND 416 out of it, simultaneously."

The problem is that you already have a neutral in a Y system.

If you draw out what another center tap on the 240 V to provide 120 V does, you will see a problem.
One of the Y legs has a short across half the winding since the two neutrals would be at the same voltage (o volts and tied to earth ground).

You could do center tap one side of a delta and put the neutral there, and this is what the 'wild leg' system does.
Since a delta system has no neutral, it works.

"You could do center tap one side of a delta and put the neutral there, and this is what the 'wild leg' system does."

And that's what I was talking about - and you now have four wires, delta, 120, and 240... and I THINK the other leg is still 208 from neutral...

I mis-spoke, of course, there's no 416 here.

A wild leg system starts as a delta 240 V.
There is no neutral, so the 240 V is line to line on all 3-phases.

You then use a transformer to create a 120/240 V leg one ONE side of the delta.
The middle of the 120/240 V becomes the neutral, and while the 3-phase is still 240 V delta, the 'wild leg' is 208 V from the neutral.

The wild leg phase is opposite the center tapped 120/240 V leg o the delta triangle.
It ends up at this since3 it is half of a 240 V, or 120 V plus the 240 V at angle 120 degrees.

Alright, since there's going to be dispute over it, I'll stop speculating and trying to describe my mental image to someone who will not receive it. I will instead google it.

And here it is. This is the power company's transformer or bank. The "PA", "Primary B", and "PC" connections are the high-voltage ones on the top of the utility pole. The power company provides "Center Tap" (NEUTRAL), "SA" (ONE 120V LEG), "SC" (THE OTHER 120V LEG), and "Secondary B" (THE 'HIGH' LEG) to the customer.

The customer gets four wires, enumerated above. The customer gets a 208-to-neutral high leg and two 120-to-neutral legs with 240 between them, without installing his/her own transformer. The poco transformer does it all, and no more transforming or other alteration is necessary on the customer's part to get 120, 208, and 240 from his "4-wire 120/240 delta", or "High leg delta" service.

In fact, being an "open delta" makes it a little more complicated than that and may affect my plans for the property. I have not reached the bottom line yet.

You can find schematics with a google search very quickly.

I had hoped that someone else would ask the obvious question. Why would this system ever have been specified and installed in a single-family home? Certainly not to reduce construction costs. Certainly not to reduce construction costs for the power supplier.

In the location where *I* found it, it was a building that had originally been a dairy farm, and got converted.

My assumption is that ionized's location has a similar story.

The house was built in about 1920 in an area that was residential in nature at that time. I don't know what was considered normal service at that time. Its most recent owner was an electrician. I suppose it is possible that there was three-phase ac at one time. My 1950 house in a different neighborhood was one of a number of houses there that were equipped with three-phase AC compressors condensers and water-cooled condensers. It was never a farm or any other kind of business. I will keep my eye out for clues and I may get an opportunity to ask the family.

My understanding of the type of three-phase service is that it is fairly common and used when three-phase is desired, but not predominant. It is cheaper for the power company to provide because it requires at least one less transformer.

3 phase is not allowed by electrical code for townhouses, 1 and 2 family residential dwellings.

Period.

End of discussion.

If you have 3 phase, you either have a commercial building or have a VERY BIG problem...

And just what code prohibits 3 phase from entering a dwelling?

The NEC is silent on this.

What other code prohibits 3-phase in residential?

I have just one little piece of added info. The house next door is also three-phase. My wife knows the guy through professional contacts. I called him today to give him an update on the purchase process. (We will likely close on Monday.) He mentioned that he lost the neutral a few years ago and that blew out the electronics on some of his appliances.

Losing a neutral will mess with your appliances (and quite likely fry some) even on single-phase.

At long last, I borrowed a good camera and took some pictures of my electrical service. Some weeks ago, I tried with my cell phone camera but the detail was horrible so I did not post them. I did take some voltage readings. Unfortunately, I do not have access to them at the moment. They were consistent with a high-leg system. I will post them tomorrow. I think you can get to a full set of pictures by clicking on the link below.

I cut the resolution on the meter too much. It says under the "240 V" box, "4 W [delta] TWO stator".

I did not take off the inside covers. I think I have most of this figured out, but some mysteries remain. The garage has a single phase sub panel, but it looks like all three conductors are connected to the breakers that protect that panel. Maybe the conductors go back there and a single-phase panel was substituted at some time, or wires were installed so the capability was there for three phases but never used.

There are only two legs that go into the panel on the left (not the high one as you might imagine). There are two sets of breakers that are labeled "main" in the right panel. The one higher up is clearly the real main since it has the larger conductors connected to it. The lower one is labeled "main" and "next panel". There is also another triplet of three tied breakers in between those two sets.

There are no three-phase loads on the property at this time. I had a short discussion about with the seller about some weird electrical equipment in the attic. They were for a central AC, water-cooled and 3-phase, system that he described as a "monstrosity". Keep in mind that he was a kid when it was removed. Keep in mind, too, that I previously owned a 1950 house that was originally equipped with 3-phase, water-cooled central AC. In that case the whole service had been changed to single-phase before I bought it.

I suspect that the two, unidentified, sets of three-phase breakers supplied the old AC system, but I will have to dig further to get to the bottom of that.

LIne to ground or neutral was 122 for two main conductors and 216 for the one wrapped with orange. Line to line were all between 247 and 250. This was with a digital multimeter.

If some of you electrical code knowledgeable people could take a look at the pictures, I have some questions for you.

I am wondering if this was ever code-compliant. It is certainly way off from a typical electrical service. First, is that unprotected junction/splice between the meter and the panels allowable or advisable? Second, between the split bus panel and the other, there are, potentially, 7 handles that need to be thrown to completely shut off the power. I understand, mostly from reading here, that 6 was the max until 1968 and it is 1 since then. You can see that only three sets of "main" breakers are installed in the split-bus panel. (I think only two of them are being used at this point.) Does that make it OK? Following on to that question, can I install up to a total of 5 in there? (I am considering adding more 240 V loads, though they would only be 20A.)

The "three-phase" panel looks like it is supposed to be installed as a sub panel, right, since there is no place for a real "main" breaker. Is this allowable?

Lastly, are I-T-E class N. I. type EQ-P circuit breakers available?

"First, is that unprotected junction/splice between the meter and the panels allowable or advisable?"

It is in a box.

Not all wiring before a main requires protection.
The main prevents overload, while the POCO provides the fault protection. This is the typical method on most service entrances.
No over-current device is required before a main.

It may be that an AHJ let it go since it is all outside anyway and they were trying to keep costs down.

It does look a bit like a kludge.

If you replace each panel with ones with a single main it would be a lot cleaner.

If the house had two apartments at some point it might be a little more understandable.

Thanks, brickeyee. I rarely see electrical service equipment indoors in New Orleans. I think it is highly unlikely that the house was ever divided.

I suspect that the previous homeowner installed some panels that he had on hand and they might have been used. There are a lot of light fixtures around the property that are probably salvaged. Recall that he was an electrician. I have other indications that he was pretty tight with his money. That, and the fact that he moved towards an all-electric house might explain why he felt he needed two panels. I am sure the original cooking equipment was gas. That was changed to electric in the early 60s. Sometime after that, he replaced the gas water heater with an electric one, and did the same with the dryer. That left only the central heat furnace and decommissioned gas wall heaters.

The panels, typically for this region, are pretty corroded. That is the North side of the house under a gable so they are often wet. Even though they are not in great shape, I wont look forward to replacing them soon because there are MANY other things that need doing around the house, roofs, floors, AC,. If I go to the trouble of replacing the panels, I might as well ask the power company to put me on a more conventional system as it would probably save some headache down the line.

You cant tell from the low res picture that I put up, but I would rate the age of the components: mast = meter pan The history of power to this house might be interesting. I think I see one spot with some disconnected knob/tube. This house was built before central air, but three-phase might have been added to power an early adopter of that technology. The house next door has three-phase power with an ancient meter that looks like a cabinet with a glass window.

At the same time the homeowner was frugal, he enjoyed convenience. So far, I have found 5 switches controlling one garage light. I thought there were 4, but I found the 5th one last week :-) There are 4 switches controlling a hall light. Not unheard of, but unusual in my experience are the split outlets in the living room. A photocell-controlled outdoor spot light is typical, but the same circuit controls a convenience outlet in the BR. All you have to do is remember to turn the lamp on in the morning and a light will come on to greet you if you are not home before dark.

A little more information tricked in. I have an outfit looking at my house for net-metered photovoltaic power installation. The young owner claims EE and master electrician status. He checked with the power company and told me that the transformer is "likely intended" to see three types of loads, 120 V split phase, 240 single phase and symmetric three phase loads. Furthermore, it is "probably not designed to see unbalanced loads on the high-side phases".

He seems a little unsure of himself since he used the qualifiers "likely" and "probably". He "probably" has it right and has to fudge because of imprecise communications from the power company . For net metering, He would just connect the inverter output to the 120/240 split phase just like in any other home. If someone gave me a three-phase inverter and some solar cells, I could probably have it connected like it was a typical three-phase, but I would not go out and buy a three-phase inverter system.

Right now it seems like I have an electrical service with 72 kW available, but I can only use 48 kW since I have no three-phase loads. That boils down to the same as anyone with a 200-amp split-phase service, so I guess I should not feel like I got cheated.

http://yfrog.com/5mswires001jx
{{gwi:2097938}}
Well THERE'S yer problem!

Please disregard. That was meant for another thread!

I'm a sped this week.

I talked with a couple of local HVAC contractors this week. They have been working in the area and in the field for quite a few years. They both looked at my drop and said that ca. 1950, anything over 3 tons of AC got three-phase.