Ok, this is my "dumb" question of the day:

When you go to the main CB panel (residential, commercial, or industrial setting), how do you tell if the feed is from a Wye or a Delta?

I'm either going to learn something new... or I'm going to feel pretty "stupid" when I get the answer from you all. (hey, I've felt stupid before)

Steve

I would think a combination of visual examination and voltage readings would do the trick.

If there's no neutral conductor on the service bonded to ground, it must be delta.

If one conductor is grounded and there are only two other service conductors, it will be a corner-grounded delta, and you'll get the same voltage reading between the two hot legs and from each hot leg to ground.

If there are three conductors plus a grounded neutral, it could be wye or 4-wire delta.

Wye will show the same voltage from each phase to ground; 4-wire delta will show the characteristic "high leg" voltage on one phase.

No such thing as a "stupid" question, if it is asked....

If you don't ask, how are you going to get the answer?

I agree with pauluk, voltage measurements would do the trick.

Do a search in the theory section under wye and delta. The guys here were nice enough to post schematics, and voltages for everyone to use. Take a look and ask away....

Just like a lot of other things, the Americans are conveniently backward.
Delta-Star Tranny's are used here to supply LV 400/230V installations.
No bad combinations, no 120/240/277/460/480, you name it combinations, why does the US always have to be a PITA and be different??.
The rest of the world is 50Hz, Grow up!!.
And don't get me started on Metrics.

Maybe, because we did it first, and other folks decided to be different from us?

Maybe it is because we have had electricity longer. You guys have been dealing with it, what? 60 years or so? When was it that the US Army wired up that place?
;-) sorry

Seriously, part of the problem here is that we have reminants of the Edison vs Westinghouse wars from the early 20th century and some folks won't change. We are lucky not to have DC grids.
Once you come down off the national grid the local power companies are free to offer whatever they want or whatever the customer wants. You can make a case for any of the various schemes that enter buildings.
Life might be easier if we did have a single national standard for services but then the IBEW would lose some of the mystique that makes it the sectet society it is.

Metrics is another whole question. That is a commie plot and we think the French were behind it. ;-)
Some believe it was just a way to charge the same for a smaller bottle of whiskey. (750 vs a "fifth")

Mike




Can you tell me why any of those combos are any better or worse than another?

Is it not better to pick a voltage for conditions than to be locked in with only one option?

Bob



[This message has been edited by iwire (edited 06-27-2006).]

I don't think the voltages themselves are a problem - but arrangements like corner grounded delta or 4 wire delta do seem somewhat overly complex for people who see on a dailoy basis you can live perfectly with 4w wye supplies and loads that are either connected in wye or delta.

Man, don't get me started on 50Hz! I work sites all around the world, and every time we have 50Hz it's a headache. The voltages aren't that big a deal, but having to derate all these UPS systems because the magnetic flux is saturating the transformer core is just killing me... Wanting a 750kVA and having to pay for a 750 but only getting a 625, man, it hurts. Can't even throw money at 'em to rewire the transformers with a different core because the 50Hz transformers are too big! 60Hz is 20% more efficient, why don't ya'll just give it up and switch to 60Hz? All your motors and transformers would be smaller and cheaper ya know!

The worst is when there is a mix of US and european voltages and frequencies, that tends to get messy...

[This message has been edited by SteveFehr (edited 06-27-2006).]

I think corner delta is one of the best solutions out there. If I just have 3 phase loads I can do the whole thing with 2 pole equipment that basically looks/costs like single phase.
We did a lot of pumping stations this way.
You just need to be sure it gets serviced by qualified people who know what is going on.

The different voltages really don't pose much of a problem, Mike.

I haven't installed anything but 120/208 Volt or 277/480 Volt 3 phase services for at least 20 yrs., except for the odd one here and there that the PoCo didn't want to change out existing transformers because they served other existing services too.
(BTW, Canada uses 347/600V where we use 277/480)

Single phase services have been 120/240V That's it....

As for telling a Delta 3 Phase 4 Wire system, the high leg should be tagged or marked, BUT DON'T BET ON IT and BE SURE TO VERIFY. This was a requirement since the later '50s or early '60s. In '71 the NEC added that the high leg could be orange or marked with orange for identification.
(San Francisco requires it to be marked in Violet)

What's confusing about that??

Skingusmc - Ditto what Dnk said about no stupid questions, and back to your not stupid at all question for a moment. When you walk up to a panel or switchboard, either carefully check the nameplate voltage or take your own voltage readings (both if you can).

In a dual voltage system, if there is a factor of approx 1.73 between the voltages (i.e. 120/208 or 277/480), it's a Wye.

If there is a factor of 2 between the voltages (i.e. 120/240), it's a delta.

There are other wierd voltages for special applications (VFD's, etc), but the rules above apply. Hope this helps some.

Radar

All -

Let me also agree and state that there are no "stupid" questions (well, there was that one I asked when I was in Istanbul, but that's another story entirely)(grin).

I also knew I could get great info here, so thank you one and all.

As for the US being a PITA, it's a gift and talent!!!(grin)

Steve

skingusmc

Paul's reply is right on the money!!!

Just for fun, I will add a few things:

A: VISUALS;
<OL TYPE=1>

[*] See what the Transformer looks like,


[*] See what the Service Feeders are,


[*] See what the kWh Meter on the Gear with the Service Disconnect is rated for,


[*] Ratings for the Service Equipment - 1 Phase, 3 Phase 3 Wire or 3 Phase 4 Wire,


[*] Customer-Owned Step-Down Transformers (SDS) - are there any?
</OL>

And:

B: TESTING VOLTAGES;
<OL TYPE=1>

[*] If 1 Phase, test L-L (Line to Line) with a Voltmeter that displays somewhat accurate values,


[*] If 3 Phase, test L-L between A-B, B-C, and A-C to see if you get an average reading for the 3 phase voltage,


[*] To verify a 208Y/120 3 Phase 4 Wire Wye System, vs. a 240/120V 3 Phase 4 Wire system, test L-G on each of the 3 lines,


[*] To verify Ungrounded 3 Phase 3 Wire Delta Systems, vs. Corner Grounded / Center Tap Grounded 3 Phase 3 Wire Delta Systems, test L-G on all 3 lines with a "Wiggy" type Voltmeter.
</OL>

Explanations:

Lists in "A":

"A1":
Visual check of the Transformer Network of Pole Mounted Transformers, to see if the service is Single Phase, or one of the various 3 Phase types.
For assistance on Identifying 3 Phase arrangements, see the Technical Reference section for Transformer Schematics.

"A2":
Service Feeders- if overhead, you may be able to identify the system by number of conductors &/or size of conductors.
For example, 3 service feeders would indicate either a 1 phase 3 wire service, or a 3 phase 3 wire service.

4 Conductors of equal size would indicate a 4 wire Wye, whereas 4 conductors with one conductor being significantly smaller than the others (or two small ones, and the other two large), would likely indicate a 4 wire Delta service.

"A3":
The kWh Meter will display ratings for Voltage and system type.
4 Wire kWh Meter are listed as "3 Stator" types.

"A4":
The Service Equipment should have nameplate ratings for the Amperes and Voltage, along with "Neutral Voltage". This is not very accurate, but may uncover a 3 Phase system if only 1 Phase Panelboards are found.

"A5":
If there are any SDS Transformers, the Primary (Input) Voltage may disclose what type of service is available.
If you see "Primary = 240V Delta, Secondary = 208Y/120V 4 wire Wye", the Service might be a 3 wire Delta (also could be a 4 wire Delta, so it's a crap shoot!).

----------------------------------------------
----------------------------------------------

Lists in "B":

"B1":
Tests on 1 Phase 3 wire Panelboards to verify if the Service / Transformer is a 4 Wire Wye or a 4 Wire Delta:
Looking for a reading in the range of 208 VAC between each Ungrounded Conductor, for a Wye Connected Transformer; and in the range of 230 VAC for a Delta Connected Transformer.

"B2":
Same as shown in "B1" above - trying to get the L-L System Voltage.

"B3":
Verify Voltage on all 3 Lines to Equipment Ground - or Grounded Conductor ("Neutral").
If all 3 Voltages are equal (+/- 10%), then the system should be a Wye connection.
If one Line is vastly different than the other two, the system is most likely a Delta connection.*

"B4":
To verify if your Delta system is Ungrounded or Corner Grounded, you need to use a Solenoid-Type Voltage tester, such as a "Wiggy" for these tests; as a High Impedance Input type Volt Meter (typical DVMs) will result in inaccurate readings.

Tests to determine if Transformer is setup as 3 Phase 3 Wire Corner Grounded Delta:

1)
2 of the 3 Lines should have a "Solid" Voltage reading, from Line to Ground ("L-G"), and one should read "Zero Volts" from L-G, with all Voltage readings between the 3 Phase Conductors (A-B, B-C and A-C) being the same as the Voltage to Ground.

2)
If a 1 Phase 3 Wire Panelboard is encountered, the Voltage read between any one Ungrounded Conductor Bus and the Grounded Conductor's Bus (the Neutral Bus Kit), should be the same as the Voltage read between both of the two Ungrounded Conductors.

----------------------------------------------

Tests to determine if Transformer is setup as 3 Phase 3 Wire Center Tap Grounded Delta:

1)
Test L-G Voltage on all 3 Ungrounded Conductors, looking for one L-G test which shows a significantly higher Voltage than the other two.

---------------------------------------------

Tests to determine if Transformer is setup as 3 Phase 3 Wire Ungrounded Delta:

1)
Test L-G with the Wiggy should display a very short "Pulse" on the Solenoid, along with the Neon indicator Lamps displaying a very minute pulse, with an overall result of "Zero Volts" displayed.
FYI: these indications may not even occur at all!

2)
After testing with the Wiggy and finding the above results, using a DVM (Digital Voltage Meter) set to the highest Voltage scale possible (at least 750 VAC), test from L-G to observe the various Voltage readings.
On a 480V Ungrounded Delta, values of 300 VAC to 500 VAC as measured from L-G at the Service Equipment are normal.

3)
With the DVM reading a Voltage between L-G, have an assistant place the Wiggy's test probes between L-G on the same "Phase" as the DVM's test leads are on - and as close as possible to the DVM's leads.
This should result in the DVM's readings being dropped to near zero volt levels - possibly maintaining at a level of around 35 to 100 Volts maximum.
Remove the Wiggy's test lead, and the DVM will begin accumulating an increasing Voltage reading, until it peaks off once again.

BTW - if you are familiar with Capacitors, you will recognize the ways these Wiggy / DVM tests affect the Capacitive Charging effects on the system.

Good luck!

Scott35

edited to correct type of Power Meter referred to
(I played the Dumb-Dick card, and typed "KVA Meters", when meaning "kWh Meters"!!!)


[This message has been edited by Scott35 (edited 06-28-2006).]

Having learned about the various U.S. systems from an outsider's perspective myself, I can see how it might appear that there are far more combinations than necessary compared to other parts of the world.

Examining the situation more closely, however, there's a lot of sense in choosing the voltage level, wye/delta arrangement etc. to match the need rather than having to force everything onto a "one size fits all" supply.

The 2:1 ratio of many of the voltages also makes it relatively easy to make motors and similar devices dual-rated for 120/240 or 240/480V use by series/parallel strapping of windings.

The high-leg 4-wire delta did seem a strange beast to me at first, but when you look at the reason it originated (to provide 120V for general loads from a basic 240V delta system), it actually makes perfect sense. Why go to all the trouble and expense of providing a separate transformer (PoCo- or customer-owned) for your 120V loads when you can get 120 by just grounding a center-tap on one side of the delta?

With regard to supply frequencies, it would be nice if the whole world could use the same standard, but I suspect we're way past the point of that being a practical aim, at least not without major disruption. North America (not just the U.S. but also Canada, Mexico, and some of the Caribbean) and Central America already have so much 60Hz equipment and Europe, Australasia etc. already have so much 50Hz that to change now would be a mammoth task.

In the U.K., we only standardized on 50Hz with the plans for the national grid in the 1930s. Prior to that, each generating area could use its own frequency: 50Hz, 40Hz, 25Hz, etc. Remember we've had similar discusiions here in the past about non-60Hz systems in the U.S. (e.g. the Los Angeles area changed from 50 to 60Hz in the 1930s, parts of upstate New York had 25Hz until the 1950s.).


A few months ago somebody in a telecom group asked (with a decided anti-American sentiment) why the U.S. "decided to be different" with its area code numbering and dialing plan. He thought the U.S. should have adopted the "worldwide" standard of dialing zero in front of an area code etc. Answer: The U.S. system was developed before the others, so if any accusations are to be made, the pertinent question would be "Why did the others not follow the existing U.S. standard?"

Scott35,
Good answer.
One point on the Kwh meter. With the newer solid state meters, many forms of metering are being combined so that one meter often works on wye and delta systems. To add to the confusion, they are often free ranging on voltage. So the nameplate may very well read, "120 to 480 volts).

Remember not to believe everything you read.



Lots of guys do it wrong

Testing, like Scott said, is the only sure way to know for sure.

Good Lord!!,
I said that??.
My apologies to all not only in the US but to all at ECN for having to read that sort of drivel.
That was ABSOLUTELY not the tack I was trying to take.
Each system to thier own I say.
Sorry guys.

I am surprised nobody mentioned the size of the transformers. If you look at the pole that feeds the building and the bank of transformers has one thats larger than the other two or two transformers with one larger than the other it's a 240/120 delta. Three pots of the same size...wye. Always test to be sure but different size transformer pots screams high leg.

If you see something that looks like 3p with 2 transformers that is usually open vee delta.

Electure,
I think John (renostienke) bought up panel marking some time ago.
I'm all for labels that we all can read, not just the person that wrote them, after all, whose to say that he/she is going to be there to read them next week, next month or in fact next year?.
I used to use a Brother(Shameless advert I know, but you get the drift) label-maker, if you can't read the labels from one of them, you need help and fast!.

{message edited for bad spelling}

[This message has been edited by Trumpy (edited 06-30-2006).]

The deal with the picture I posted is this......
A 120/208 system is a Wye, and there is no leg with a higher voltage to ground/neutral. The system pictured is a 120/240 3Ø 4W Delta.

The Code requirement is that the Ø with the higher voltage be used as the B, and not the CØ.

Like Gfretwell said, you have to have qualified people. (the same could apply to a duplex receptacle)This one obviously wasn't, but also saw fit to write "Installed by", with his name, on another part of the panel.

Doing electrical measurements between phases to ground will help you accomplish what you are trying to achieve. i prefer wye in most commercial/industrial applications myself because of the load balancing characteristics you are able to achieve with it, however Delta 4 wire systems also has a distinct advantage over wye systems in that if one transformer is lost in the utility bank, you can always T the other two and still achieve a three phase system. Corner Ground systems should just be done away with completely. We owe our gratitude to Mr. Nikola Tesla for three phase. And as far as the rest of the world, well..........Just steal the information and copy us, that's what youre truly good at.

Why?

A few links:
http://www.teal.com/products/App%20note%20AN-15.htm
http://www.phaseconverterinfo.com/phaseconverter_delta_wye.htm
http://www.federalpacific.com/university/transbasics/chapter3.html

Reading the labels can give you a clue, but always measure. I recently found a 208 3-phase receptacle that was wired up as a single phase for 8 years, feeding a 3-phase transformer. That really made for some strange measurements and head-scratching...
/mike

*** BUMPING THIS THREAD UP AGAIN ***

Just wanted to bump this up again, since the information is really interesting and may be of assistance to others.

Scott35

scott35, i have a transformer connection manual that shows the hi leg of a 120/240 volt delta on "C" phase always. but you say code says should be "B".wonder why the difference? BTW it's a GE transformer connection manual. one other ? why is the hi leg 208?

Let me throw in my two cents... not that I disagree with anyone (I don't), but my approach is a bit different.

When I open a panel, I first look at the lugs. Two hot wires = single phase. Three hota and it's a three-phase.
Now, is there a neutral?

Checking volts line to line, "240" suggests delta. "208" suggests wye.
Checking volts line to ground. Does every leg have the same reading? If not, it's a delta. One "high" leg, and it's got one transformer winding grounded in the center, to make the "neutral." One leg reading "0", and it's a 'corner grounded.'

Now, look at the pole. One big, and two little transformers... the big one has the center tap for the "neutral." Two transformers, and it's an "open delta." One transformer, and it's single phase.

Know your "nominal" voltages: 120, 208, 240, 277, 480. If any of your reading vary from these by more than, say, 5%, there's something goofy happening.

The only problem with your method is a corner ground may present you with 2 blacks and a white with 2 pole breakers.
It looks like a garden variety 120/240.
Line to ground will be 240v. That is the tipoff. It should also be labelled if the installer wants to help the next guy.
The first one I saw confused the hell out of me. Three transformers, 3 phase motors and single phase <looking> equipment. I was there alone so I got out my trusty meter and figured it out before the other guys got there and I had a chance to say something dumb.

Circuitman:


As viewing the 4 Wire Delta Transformer Network (3 interconnected Single Phase Transformers),
the Lines (or "Phases") encountered would be:
*** "A" ***,
*** "N" ***,
*** "B" ***,
*** "C" ***

On the Transformer which uses the Center Tapped Secondary Winding's Terminal Bushing, the first Line Conductor (on the left side) would be Line *** "A" ***.

Next to it, and in the center of the three bushings, would be the Grounded Neutral Conductor - or Line *** "N" ***.

The last Line Conductor (on the right side) would be Line *** "B" ***.

Line *** "C" *** is the from the Paralleled Termiantions, which tie the farthest _LEFT_ side Secondary Bushing's Terminal on the _LEFT_ side Transformer, to the farthest _RIGHT_ side Secondary Bushing's Terminal on the _RIGHT_ side Transformer.

When the Service Entrance Conductors are ran into Service Equipment, the "Rotation" follows the "Right-Hand Test-Bypass-Block As Power Leg" configuration. The Conductor on the "Right-Hand Side" is the one tagged Orange (the High Leg).
The "Rotation" stays this way, until the Feeders reach "The Customer's Side" (normally, the "LOAD" side of the kWh Meter).

This is the point where "NESC" and "NEC" begin and end (in a matter of speaking!).

The NESC "Ends" on the LOAD side of the kWh Meter, or at the LINE side of the Service Disconnect.
Where the NESC "Ends", the NEC "Begins".

NEC wants the Orange Colored Conductor (the High Leg), to be in the *** "B" *** Position, on the Bus Kit of 3 Phase Panelboards, Switch Gear, and Disconnect Switches.

If the Grounded Neutral Conductor (Identified Conductor, or simply "The White Conductor") is "Used" in any 3 Phase Panelboards, Switch Gear, or Disconnect Switches "Downstream" of the Service Equipment, then the Line *** "B" *** "High Leg" shall be tagged Orange.



This one has been covered a few times before, but it never hurts to ask when needed!

The "High Leg" on a 240/120 VAC, 3 Phase 4 Wire Delta system is approximately 208 VAC to Ground (to the Grounded Neutral, or more correctly, the Center Tap of the 1 Phase 3 Wire "Section" of the configuration).
It may be 190 VAC to Ground, it also may be 220 VAC to Ground - all depends on the loaded conditions of the Transformer Network.

Typically, the "High Leg" will be 1.732 x the L-N Voltage of the 1 Phase 3 Wire "Section" - which equates to roughly 208 VAC.

Simplest explanation of why this equals out like it does:

Phase Shifts and a Series Adding Winding configuration.

Detailed explanation:

Too much stuff to type out at this time!

Best if you perform a search in this forum area, along with the Electrical Theory section, using a topic like "4 Wire Delta", or "Transformers".

Good luck.

Scott35

All -

Once again thanks to everyone that has provided information and insight.

I know I can always get great answers and learn things here.

Steve