Three phase

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charlie b said:

Depends. Which side were you on?
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Haha, good one.

Well I was under the impression that it always has to be a Wye, (480/sqr(3)=Vline, right?) my friend who is not an electrician argued based mostly on the fact that it is not labeled as a Wye (480Y/277) and thus cannot be.

Is there some sort of standard practice for these labelings? Based on this thread I would venture to say that there isn't any such standard.
 
RichardM said:
Is there some sort of standard practice for these labelings? Based on this thread I would venture to say that there isn't any such standard.
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Yes there is, see 220.5(A)

Roger
 
RichardM said:
Just a quickie: Someone is arguing with me whether 480/277 is always wye or not.
Could you please reassure me that I am not insane?
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Not insaner than the rest of us:D

Somebody COULD construct a single phase transformer with a 480V single phase secondary and a 277V tap, or even a three phase delta with taps, but wye,uh....why would one want to do that?

The proper designation for those would/could be 480/277/203V.

So Who is on first......:smile:
 
Volta said:
Do you know then how they designate single-phase 240/120?
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120/240V is the correct method for describing single phase 3-wire.

I am not trying to be pendanic, as much as trying I am trying to avoid future confusion. After all, the NEC uses these methods in its definition of Voltage, Nominal and in 220.5 for calculations.

I know old bad habits die hard.
 
I've been reading this thread and don't know a thing about what you guys are talking about. I'm just an inspector and I would like to learn more about the commercial end. I guess this is more commercial...right?

I've always heard about single phase, three phase, wye and delta, but this is so far over my head I have to commend you guys for your understanding of this jibberish.

I always thought 240/220 were all the same...then someone throws out a 208.

Is there someplace that can explain this to me instead of me thinking I know what the heck I know!
 
GrayHeadedMule said:
I've been reading this thread and don't know a thing about what you guys are talking about. I'm just an inspector and I would like to learn more about the commercial end. I guess this is more commercial...right?

I've always heard about single phase, three phase, wye and delta, but this is so far over my head I have to commend you guys for your understanding of this jibberish.

I always thought 240/220 were all the same...then someone throws out a 208.

Is there someplace that can explain this to me instead of me thinking I know what the heck I know!
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To simply put it:
240/120 is what you see on the pole before it gets into the house, 230/115 would be at your panel in a private homes area. These are single phase systems.

Since the 115V voltage is a common applicance, lighting and receptacle voltage, for large users such as office building or hospitals etc. three phase systems are used. (All power distribution in the US originates from a three phase dsitribution system, even the single phase mentioned above.) To efficiently use the system capacity, you would want to balance the load between the three phases. In the home-feed distribution the Utility accomplishes this by alternating the primary phases from trasnfomer-to-trasnformer as they go down on the line. Large users use three phase systems. A three phase transformer is either delta where three widnings ends connected to each adjacent pair, forming a triangle and the connection points are the power supply or source. The wye system uses the same three windings, but only connects/commons one end of ALL three windings. The three 'free' ends become the power source for each phases and the common point is the one that is connected to ground and becomes the neutral. The magnitude of the volage has to do with math, but it is easy to remember. The voltages measured between the free ends are the line-to-line voltages and the end to the common point is the line-to-neutral. The relationship between the two voltages is Square Root of 3 or roungly 1.73. This results in 480/277V and 208/120V.

Are you an electrical inspector? Is it your responsibility to inspect according tot he NEC?
 
Thanks for the tutorial. I'm a building official. I'm also a certified residential electrical inspector and pretty good at resisidential electrical. I'm weak in commercial.

Yes I inspect commercial but I have to rely on the master electrician to "do it right". The commercial jobs we do are designed by an electrical engineer and I inspect according to plans. It's the Delta's and wyes is where I'm lost.

Working for a municipality in Texas the state doesn't require electrical inspectors to be certified. What is REAL SCARY is that I have heard from a reliable source that the new Cowboy Stadium in Arlington Texas has so many people working on it and so many inspections are needed to continue to on with construction that they have sent code enforcement officers (grass and weeds) to perform electrical inspections. Don't know if it is true or not but I wouldn't doubt it!

Inspection departments are always required to do things that they may not be experienced in. Especially in smaller cities.
 
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ANSI C84.1-2006, For Electric Power Systems and Equipment— Voltage Ratings (60 Hertz) is the US Standard for nominal system voltages. It “…establishes nominal voltage ratings and operating tolerances for 60-hertz electric power systems above 100 volts.” It is published by NEMA.

Since they are “nominal” they may not be absolutely exact if measured, but they should fall within fairly narrow tolerances.

The standard values are derived from a multiple of 120V, a multiple of 120V x sqrt of 3, or a multiple of 120V / sqrt 3. The values may not be exact but are within the standard tolerances. Not all variations are used, but many are.

The standard typically notes the appropriate “Y” value of a three-phase system.
 
Nine nominal voltages in the US can be found in the NEC 220.5(A).

Nominal system (source) voltages of 110V, 115V, 220V, 230V, 440V, and 460V have not been recognized by IEEE or ANSI for almost 40 years, even though utilization equipment (i.e. motors) continue to use these values on their nameplates.
 
roger said:
Yes there is, see 220.5(A)

Roger
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So how come this panel box gets away with failing to label it a Wye? Wouldn't this be considered a fineable offense?

Because from the responses in this thread, it could be a number of odd situations that would allow for a 480/277 system while leaving a humble person to being none the wiser.

By the way, maybe an image will clear things up a bit. If you can give more insight on it, that would be great:
boxtc3.jpg
 
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RichardM said:
So how come this panel box gets away with failing to label it a Wye?
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Because there is nothing saying it has to include Y in a description and, "277/480 3? 4 wire" can only be a wye configuration, this is enough.

A 480y/277 volt service is a very common (everyday) system where I am. It is very rare that I go into a commercial building that is not served with this system.

RichardM said:
Wouldn't this be considered a fineable offense?
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No more so than someone calling a receptacle a plug. :wink:

Roger
 
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RichardM said:
So how come this panel box gets away with failing to label it a Wye?
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It may come as a surprise but manufacturers are not subject to the NEC.:smile:
And as I said before, old habits are hard to break.

In the electrical industry, in the US, there are many standards but there are few requirements. Most of us live in our own small worlds and understand the context in which our world uses terms. However each world is a little different and so when we do not understand the context, meanings of abbreviated phrases and terms get confused. As Roger said, in the world of switchboards and power equipment 277/480 3Phase 4Wire is immediately understood to be identical to 480Y/277, but to someone from only the single family residential world that same phrase may raise questions.
 
RichardM said:
So how come this panel box gets away with failing to label it a Wye? Wouldn't this be considered a fineable offense?
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The wye has nothing to do with the panel, and everything to do with the xfrmr. I've got a feeling that the panel manufacturer could care less what kind of transformer feeds it. The voltages stamped on the plate are what it has been designed and tested to be used with.

Regards,
Doug S.
 
RichardM said:
Haha, good one.

Well I was under the impression that it always has to be a Wye, (480/sqr(3)=Vline, right?) my friend who is not an electrician argued based mostly on the fact that it is not labeled as a Wye (480Y/277) and thus cannot be.

Is there some sort of standard practice for these labelings? Based on this thread I would venture to say that there isn't any such standard.
Click to expand...

A power source would bear the identification of wye connection, but in the case of distribution equipment it has no meaning.
 
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