1ph 3 ph help

On 7 Jul 2004 08:08:38 -0700, Brad put forth the notion that...

A 120/208 Wye system has no high leg.

That's correct.

He shouldn't have fed a 120/240 volt single phase panel with two legs of a 120/208 Wye. First of all, it's going to unbalance the three phase load. Secondly, it's not going to give you 240 volts unless he uses a transformer.

| need help clearing up this issue. Some electricians that work for me | often ask me is something is 208V single pahse or 3 phase. In these | cases there is no high leg system, so as I understand it 208 single | phase can't exist without the high leg. I always assume they are | talking about a 2 pole breaker in a 3 phase panel. Am i right about | this, or am I missing something.

There are 2 different power configurations generally wired 3 different ways in common use that can give you 208 volts:

The 240 volt with a center tapped winding for lighting gives you 208 volts between the high leg and ground:

• / \ / \ / \ / \ / \

*-----*-----*

You can also make the same configuration like this:

• | | | | |

*-----*-----*

by tapping the primaries in a way to get a 90 degree phase angle and supplying that phase angle at 208 volts relative to the neutral of a regular 120/240 transformer.

Then there is the WYE configuration:

• \ \ *-----* / /

*

Which has 120 volts between any leg and ground, and 208 volts between any two legs.

| Also I have an electrician who wired some panels for a job we are | doing. He used a 200A 120/208 3 phase panel and installed a 2 pole | 100A breaker to feed a 2 pole 125 A panel. The smaller panel he refers | to as the 120/240 panel (residential type.) I know the phase angles | relative to each other are still 120 degrees. True 120/240 panels have | the same phase thus same phase angle right. So what is this smaller | panel 120/208 2 pole???? And wouldnt this configuration cause an | unbalaced condition on the 200A 3 phase panel? | Thanks

The smaller panel is getting just 2 of the 3 phases. And yes, there is a 120 degree phase angle instead of the usual 180 for single phase. And that does deliver only 208 volts to what might be an appliance expecting

240 volts. And yes, there will be an imbalance because power is drawn only from 2 of the 3 legs for the single phase panel.

If you do have three phase power, it would be better for balancing to run all the 120 volt loads right from the three phase panel. And if you are going to run anything from 208 volts, you get that by putting a 2-pole breaker in the three phase pnael. If you have 3 such 208 volt loads with their own breakers, you and arrange those breakers to put each circuit on a different pairing of hot wires.

If the total number of poles of all the circuits would fit in the main panel, I would have just done it that way (one three phase panel). And even if a 2nd panel was needed, I'd probably have done it as three phase as well. You are not going to magically get 240 volts by using a single phase panel (you'd need expensive transformers to do that).

This is all part of the hassle of three phase power in a world with mostly single phase loads. In Europe, they have 230 volts (plus or minus 10 volts) between any leg and ground. That voltage has allowed them to power stuff we would normally use 240 volts on with what they power everything else with. They can do that with a single pole of single phase power. What that means is there has been almost no need for double voltage, so almost nothing exists for 460 volts, since 230 volts is adequate for so many more things. For very high power loads, then they go with three phase and get 400 volts (and occaisionally a 230/400 volt 2 pole scheme like the single phase panel described above). So mixing single phase and three phase in Europe is easier because they don't have the issue of many common devices wanting "2x voltage" like we have in the US.

Had the US adopted universal three phase, it might well have been 208Y/120. Appliances that need more than 120 volts would then have been designed for

208 volts, not 240 volts. But that would have meant running three phase everywhere, and that costs a lot of money in rural locations. It was electrical rurification that shut out three phase power. But it was the lower 120 volts that forced the issue of 240 vs 208. Had the US decided to go with 277 volt single pole single phase to homes (and "one upped" the Europeans on the voltage), we wouldn't have this problem. We'd have stoves, dryers, and air conditioners running on 277 volts, and then only occaisionally someone needing 480 volts for big things like saunas and kilns. We'd also have a slightly lower population because back when the big decisions like this were being made, we really didn't understand electrical safety very well, and hadn't yet invented the ground fault interruptor. But I'd say more people were killed by grounding ignorance than were saved by having only 120 volts instead of 277 volts.

In Japan, single phase is 100/200 volts, and three phase is 200Y/115 volts. I don't know if commercial offices that get three phase run their lights on 115 volts or not. I do know half the country is on 50 Hz (east) and half on 60 Hz (west). That makes for a fun electrical grid. As far as I know they don't any higher voltages until you get into primary power well over 1000 volts.

X-No-Archive: Yes

208Y/120V (the "Y" denotes it's a WYE system) is a fairy common system in a larger setup with a need for a lot of 120V loads such as dormitories and apartment complexes.

On 208Y/120V system, there are four wires. A, B, C and Neutral. Between any two hots is 208V, any one hot and the neutral is 120V. I believe they only use this configuration when most of the load is 120V plug in stuff.

They try to balance the load by spreading out the phases.

Example: Apt 1,4,7,10 gets A, B and N 2,5,8,11 gets B,C and N; 3,6,9,12 gets A, C and N.

The idea is to come up with a configuration that's least likely to result in a unbalanced load under all foreseeable conditions and I'd imagine it's not exactly an easy task.

If you have a six floor dormitory building in Texas with the first two floors on A,B; middle two on B,C; and the top two floors on C,A and they decide to make a rule that only first two floors are permitted to have window A/C's then they're going to have a serious inbalance between amps per phase between A/B and C.

Brad wrote:

Wrong, 208 volt 3 phase is 3 equal legs of 120v a 240 volt 3 phase has a high leg, typically, legs are ~120-190-120 volts

There are a lot of apartment buildings around here that are fed from 208v single phase and then distributed to the apartments as single phase 208v.

I always assume they are

Maxium size of the panel is irrlevent to the load or the breaker protecting the panel. panels start out around 60amps then go to 100, there are residential panels that are 125, 200, 225, 400, 600, 800

I know the phase angles

Single phase loads when distributed properly over a 3 phase system are not a problem. Try for a 10% unbalanced load, that is reasonable and usually achievable.

| Maxium size of the panel is irrlevent to the load or the breaker protecting | the panel. | panels start out around 60amps then go to 100, there are residential panels | that are 125, 200, 225, 400, 600, 800

There are also 150 and 300 amp panels available.

While I've seen 400 amp panels in product lines designated for residential markets, they seem to have the construction of a commercial model, and the price as well. I've never seen 800 amp in residential lines. But someone who needs 800 amps at home (Bill Gates?) can well afford a commercial panel.

On 7 Jul 2004 18:44:01 GMT, snipped-for-privacy@ipal.net put forth the notion that...

I used to use industrial standup panels in large custom homes that required 400 amps, but someone came out with a model that mounted between a double stud bay (32"). It was called the Calabasas, but I don't remember who made them.

That is bad information. If it is wrong to supply a single phase four wire panel from a three phase panel it would also be wrong to supply any single phase 208 volt load from that same three phase panel. The panel that is being supplied is rated 240/120. That means it is adequate for voltages up to 120 volts to ground and 240 volts phase to phase. Using that panel for 208/120 volt feeder supplied loads is not even pour practice let alone a code violation. The only problem would arise from attempting to supply loads that are designed to run on 240 volts from that panel. If the loads to be served are any combination of 120, 208, or 208-230 volt dual rated devices then no problem arises. In larger apartment houses the service is almost always 120/208. Only one phase of the 208 is fed to each apartments distribution panel. Load balance is achieved by equalizing the total load rather than each individual load across the three phases of the service. Single family detached homes that are adjacent to apartment houses will sometimes have 120/208 service and there is nothing wrong with that. It is, however, best practice for the installing electrician to label the service equipment to indicate the voltage that is supplied so that the occupants can purchase appropriately rated appliances.

The original poster is confusing 120/208 3 phase wye connected service with 120/240 volt three phase delta connected service.

-- Tom H

On Fri, 09 Jul 2004 17:57:49 GMT, HorneTD put forth the notion that...

What is?

Why? Not that there are lots of single phase 208 volt loads running around out there anyway.

Yeah...

It's piss-poor practice in this situation.

I beg to differ. What would be the purpose of running 120/208 feeders to a single phase panel? How often do you run across devices designed to run on 208 volts single phase? Obviously, the panel is going to be used mostly, if not completely, for 120 volt loads, so why would you unbalance a 200 amp three phase service by running 100 amps of only two legs to a subpanel? He should have run all three phases and installed a

3-phase subpanel. Furthermore, he wouldn't have even needed to run 100 amps out there if he had had all three phases.

Not in most parts of the Country.

You just made my point for me. In this case, there was only one subpanel, and a full HALF of the ampacity of the main panel was being unbalanced by only running two of the three legs to the sub. If he had three different subpanels to feed and ran a different phase combination to each one, that would be a different story. Now what happens if he ends up needing to supply a large three phase load from the main panel, and two of the legs are already pulling twice the amps of the third leg... how's he going to fix that?

That much, you got right.

|> In larger apartment houses the service is almost always 120/208. | | Not in most parts of the Country.

It really is in quite many. I depends on the feasibility of using single phase transformers or three phase transformers in the project. Single phase transformers generally are unavailable above a certain capacity. Beyond that you either run everything from larger transformers or you get more transformers and divide things up more. And usually it is the utility doing this and they will choose lowering their costs over serving you with true 240 volts any day (every utility I have seen indicates that the service could be 120/208 in some areas).

On 10 Jul 2004 04:00:07 GMT, snipped-for-privacy@ipal.net put forth the notion that...

It's not at all common in my neck of the woods for residential services. The point I was trying to make, is it's extremely poor form to take a

200 amp three phase service and unbalance 100 amps of it with a single phase subpanel. One more conductor, and you can keep everything closely balanced, plus have 3-phase available at the subpanel.

BTW, you were talking about your dream house with all different voltages available. I just picked up a near-new 15 KVA 240 Delta to 120/208 transformer on eBay for $25. It was 85 miles away, so I didn't have to pay for shipping. I'm going to use one of my 3-phase converters to feed the tranny, which will give me a Wye service for testing purposes. The only thing I don't have yet that I want, is a 240 to 480/277 tranny.

Single phase (two pole) sub panels are quite cheap (in the US, anyway) and, likewise, the breakers for one and two poles (even GFCI and "arc detecting") breakers aren't too bad. If the loads don't NEED three phases, no one is going to pay for a three phase panel.

On Sat, 10 Jul 2004 11:02:02 -0400, John Gilmer put forth the notion that...

Three phase panels don't cost much more than single phase panels, and if you're going to use 1 or 2 pole breakers, there's no difference there. You're already spending money on conduit and labor, so all you're talking about is pulling one more conductor to do it right... at least that's the way I've been doing it for the last thirty years.

|> It really is in quite many. I depends on the feasibility of using single |> phase transformers or three phase transformers in the project. Single |> phase transformers generally are unavailable above a certain capacity. |> Beyond that you either run everything from larger transformers or you |> get more transformers and divide things up more. And usually it is the |> utility doing this and they will choose lowering their costs over serving |> you with true 240 volts any day (every utility I have seen indicates that |> the service could be 120/208 in some areas). | | It's not at all common in my neck of the woods for residential services. | The point I was trying to make, is it's extremely poor form to take a | 200 amp three phase service and unbalance 100 amps of it with a single | phase subpanel. One more conductor, and you can keep everything closely | balanced, plus have 3-phase available at the subpanel.

Of course if you have the whole three phase (208Y/120) and you're already stuck with 208 volts (and unwilling to pay the cost for transformers to turn it into 240), it just makes more sense to distribute all three phases around. But, breaker panels for three phase are more expensive (go price them and see).

But it's still nagging me thinking that whoever did that install of just one single phase subpanel fed from a three phase panel, was thinking that three phase must mean 240/120 with a 208 volt high leg (e.g. 240 delta with a center tapped winding). In those cases only one phase can be used for 120 volt circuits and most 240 volt circuits (though you might be able to use the 208 volt high leg for fluorescent lighting with the right ballast).

| BTW, you were talking about your dream house with all different voltages | available. I just picked up a near-new 15 KVA 240 Delta to 120/208 | transformer on eBay for $25. It was 85 miles away, so I didn't have to | pay for shipping. I'm going to use one of my 3-phase converters to feed | the tranny, which will give me a Wye service for testing purposes. The | only thing I don't have yet that I want, is a 240 to 480/277 tranny.

The real dream house will have not only 60 Hz (in all voltages up to 600), but also 50 Hz (in all voltages up to 690), and even 110/220 DC for that "Edison feel" :-)

Seriously, I assume you're using those voltages to power some things in a shop or something?

| Three phase panels don't cost much more than single phase panels, and if | you're going to use 1 or 2 pole breakers, there's no difference there. | You're already spending money on conduit and labor, so all you're | talking about is pulling one more conductor to do it right... at least | that's the way I've been doing it for the last thirty years.

If you're comparing large 400 to 800 amp commercial panels, that's true. Square-D NQOD (240/120) and NF (480/277) panels are only barely cheaper for single phase (probably accounting for one less bus bar). And these use expensive FA/KA/LA/MA series main breakers. The regular QO series (marketed for home use along with the Homeline series that has no three phase versions) has three phase models that are more expensive relatively speaking. Aside from a unit panel with 3 spaces, the smallest three phase QO panel lists for about twice the price of an equivalent capacity single phase QO panel. Much of that price is due to expensive QDL series mains for three phase (instead of QOM1 or QOM2 mains for single phase), but even the MLO panels are much more expensive in three phase. I'd say this is all a marketing and competition issue for the residential markets (note that a 400 amp panel has a big commercial panel price tag on it). And this is just comparing list price. Street prices (in big box stores) are likely to favor even more discounting of single phase stuff (I've never seen any three phase stuff there).

List prices are in these catalogs:

Catalog section 1 for QO and HOM series load centers:

Catalog section 6 for individual circuit breakers (see also section 8): Catalog section 8 for NQOD, NF, I-line, and QMB panelboards (and breakers):

On 10 Jul 2004 20:07:29 GMT, snipped-for-privacy@ipal.net put forth the notion that...

He can get 120 volts from both legs with a wye, and the same with a delta, as long as he doesn't pull the high leg over there. In fact, if he had a delta system to begin with, it would certainly make sense to only pull two legs if he was going to be using it primarily for 120 volt circuits. If it actually was a wye system, I don't know what he was thinking, but I certainly wouldn't have done it that way.

I got out of electrical contracting after 30 years, and started manufacturing phase converters... wish I had done it a lot sooner. All my machinery is either single phase or 240 volt 3-phase, but there are times when it would be nice to have a 120/208 volt Wye system available for testing or experimental purposes. I got the tranny for $25, so I couldn't turn down that deal. I'm building a 15 HP rotary converter, which will mount on top of the tranny. I added wheels so I can push it around the shop to wherever I need it. I'll add a 240 3-wire and a

120/208 4-wire loadcenter next, with various twist lock receptacles. Occasionally I get 208 volt motors, so now I'll be able to test them properly.

| He can get 120 volts from both legs with a wye, and the same with a | delta, as long as he doesn't pull the high leg over there. In fact, if | he had a delta system to begin with, it would certainly make sense to | only pull two legs if he was going to be using it primarily for 120 volt | circuits. If it actually was a wye system, I don't know what he was | thinking, but I certainly wouldn't have done it that way.

Nor would I. The way to do it depends on what kinds of loads would be present. Certainly all the 120 volt loads can be supplied right from the three phase panel (or a subpanel if needed). But if there are a lot of circuits, I believe there is a point where you could do this cheaper with single phase panels. But that would involve balancing everything across three such panels. So if it all fits in one 42 space panel, I'd go with that. But if there are more than 42 circuits (or more than slightly less if there is a need to reserve some space), I'd go with 3 separate single phase panels, either with 3 main disconnects, or all of them connected through a single main disconnect.