120/208V or 277/480V.... huh?

E
> I don't believe that this post is correct. 120/208 VAC is nominal 3 phase voltage (i.e. 120 VAC * SQRT 3) as is
> 277/480 VAC with the phase to neutral/ground voltage first.

Yeah you are correct BUT !!! And I have to emphasis this: As follows for purposes of clarification and education.

277/480volt is always 3 phase with 4 wire system
This system uses 4 physical wires
Neutral, (white striped) Hot (black, common) Blue (Blue also common) and Grounding wire conductor (color Green)

120/208volt is also a 3 phase 4 wire system
For this the grounded conductor must be white or gray only !!!
 
> 277/480volt is always 3 phase with 4 wire system
> This system uses 4 physical wires Neutral, (white striped) Hot (black,
> common) Blue (Blue also common) and Grounding wire conductor (color Green)

> 120/208volt is also a 3 phase 4 wire system
> For this the grounded conductor must be white or gray only !!!

Be wary - those colour codes do not apply all over the world.
 
> 277/480volt is always 3 phase with 4 wire system

> This system uses 4 physical wires Neutral, (white striped) Hot (black, common) Blue (Blue also common) and
> Grounding wire conductor (color Green)

> 120/208volt is also a 3 phase 4 wire system
> For this the grounded conductor must be white or gray only !!!

I believe this to be incorrect. At least where I work.
277/480
Hots are
Brown, Orange, Yellow
Neutral
Grey
Ground Green

120/208 3 ph 4 w
Hots
Black Red Blue
Neutral
White
Ground
Green
 
B
277/480 indicates a 480V wye system - 3 hots and a neutral (plus ground).
480 V L-L and 277 V L-N.

208/120 indicates a 208V wye system - 3 hots and a neutral (plus ground).
208 V L-L and 120 V L-N.

In the US there is no national standard for the color code of the hots. Most plants have some kind of practice they follow, but it is not mandated.

neutral is always white or grey. Ground is always green.

--
Bob
http://ilbob.blogspot.com/
 
I've always understood it to mean that 120/208V is the operating voltage that it can safely operate at eg. from 120V and up to 208V. This makes sense as it allows for voltage fluctuations whilst providing reliability.
 
S
Nope. First of all, that's too wide a range for about anything but a switch-mode power supply (and even there it's just for convenience -- normal supply systems and components don't need that much tolerance for voltage variation).

Also note that on a motor label for example, the voltage will be noted as "208-230/460". Read the dash functionally as "to" and the slash as "or". In this example, a slash was used.
 
but looses are higher when current is higher, so finally he can save some money if Voltage is higher and current smaller :)
 
> As for induction motors, they sometimes can be dual-tapped for both voltage choices. If they are only one of the
> other, then I wouldn't recommend using the unlabeled voltage. For the same reason as the resistive load, you could
> overamp or overvolt, causing overheating or damage to motor. If the voltage is too low, the motor might not start, or
> spin slower and likely overheat from trying to get to its rated r.p.m. (this needs to suck more amps now to spin at its speed).

undervoltage will cause more damage than overvoltage, especially when dealing with ac motors.

 
> In the US there is no national standard for the color code of the hots. Most
> plants have some kind of practice they follow, but it is not mandated.

> neutral is always white or grey. Ground is always green.

Some three phase systems have a high leg that will read 208V to ground while the other two will read 120V. 2014 NEC requires this high leg to be marked with orange tape and it is recommended to place it in the middle.
 
The 208 VAC is the voltage between two legs of a Y connected xformer or alternator. so for each leg at 120 VAC to neutral, the leg-to-leg voltage is 240*cos(30 deg)~208 VAC. Same deal with the 277/480 VAC
 
Hey guys as an industrial electrician I might be able to help out on understanding how to achieve different voltages.

First you must understand what type of transformer you are using to feed your service panel. Pay attention to the secondary whether is a delta transformation generally used for three phase motors or a Wye transformation used for lighting for example. Second look at the phase to phase voltage. Generally 480 or 208. To achieve 277 volts you use one leg and a neutral or the common. Common is the common point in a Wye transformation.Then pay attention to the type of panel. A three phase panel circuit 1and 2 will be on a phase and in the u.s. we use brown. Circuit 3 and 4 will be orange. Three phase will not need a neutral because it creates its own differential in voltage on a sine wave.

In a 208 Wye panel one leg is 120. But to achieve 240 you need to use for example circuit 1 and circuit 2 or 7 because the are on the same phase and you are strengths voltage in series. If you used circuit 1 and three you would achieve 208 voltage but will have a 1 sixtieth of a second with zero voltage. This is why the dual phase motors make more noise. The colors for this is black red and blue for the phases. In a single phase panel you can use any two circuits or a double pole breaker to achieve 240. Then use black and red for you hot. Voltage would read 120 to ground on each leg but 240 line to line. Do not try to wire anything without the experience and being nfpa 70e certified. You could cause harm to yourself or fires. Before trying to search forums to do your own electrical work just hire a qualified licensed electrician that has experience in that installation. Also think of voltage as pressure. Just because you can calculate using ohms law to save on your electric bill does not mean that you should do it. The greater the voltage the less amps with the same wattage, yes, but the force will be greater and cause damage. Vice versa. Using less voltage causes overheating because of the greater amperage.
 
A

Ananth(India)

Dear sir can u explain what is the meaning of VL- L = VL - N
(V L to L = V L to N). The means of L and N
and a 410 Kva Diesel Generator what will be the highest load and amps
 
> Also note that on a motor label for example, the voltage will be noted as "208-230/460". Read the dash functionally
> as "to" and the slash as "or". In this example, a slash was used.

FWIW with respect to [U.S.] NEMA motors,<pre>
Rating - Nominal Supply
208 - 208V
230 - 240V
460 - 480V</pre>
The latter two assume the motor leads will experience a lower voltage than nominal as a result of impedance-imposed voltage drop on the supply conductors. (Don't ask me why 208 is 208 nominal... IDK)

Additionally, convention for 3Ã voltage systems is to put the nominal phase voltage first, line-to-neutral second:

480Y/277V 3Ã 4W
208Y/120V 3Ã 4W

... the "Y" can be omitted within documentation where the reader likely understands the source configuration is "wye".

In the States there is also a so-called single phase system comprised of two line and one neutral conductor from a 208Y/120V 3Ã 4W system. In IEEE parlance, it is:

120/208V 1Ã 3W

Note, in nomenclature for one phase systems, the lower voltage is placed first, such as above and 120/240V 1Ã 3W. This supposed to help distinguish systems in discussions where the nomenclature gets shortened. For example, 120/240 (explained earlier by others) vs. 240/120 (i.e. 240/120V 3Ã 4W).
 
Sorry about my previous post displaying "Ã" instead of the phase symbol. Relatively new to site. Didn't realize this is yet another forum which permits unicode entry and preview but parses to something different in actual post.

<b>Moderator's Note:</b> Unicode entry didn't used to be a problem. It is a new quirk for some reason.
 
R

Rick Wilkinson

120/208v refers to a 2 phase panel. 120v is your voltage from phase 1 to ground or neutral or from phase 2 to ground or neutral. 208v is your voltage from phase 1 to phase 2. The same goes for 277/480v. 277v is your voltage from any phase to neutral. 480v is your voltage from any phase to phase in a 3 phase panel.

> what does it mean when something is rated 120/208V or 277/480V? What do the two numbers mean?
 
Two (or 2-) phase is not proper terminology...

120/208V can refer either to a 3-phase 4-wire or a 120/208V 1-phase 3-wire source or load configuration. In the case of a 120/208V 1-phase 3-wire source or circuit, it consists of only two lines and the neutral of what would otherwise be a 3-phase 4-wire configuration.

IEEE convention for specifying these two variations are supposed to be...
120/208V 1ø 3W
208Y/120V 3ø 4W, "Y" optional
(Note forum in past has parsed the phase symbol so it may appear as a ?)
...but not everyone adheres to this convention.

The same is true for 277/480V but either a 277/480V 1-phase 3-wire source or circuit would be quite rare.

A two- (or 2-) phase system is a totally different "animal".
 
220V single phase service doesn't exist in the US. It's either 120V/240V (2-pole generator) or household-power 120V/208V (3-pole generator with 3-phase).
there is no 110V, 115V, 220V nor 230V in the US.
230V/ 400V is Europe.

>What about the reverse? Can you power something rated for
>208v with 220v single phase service?
 
There can be 110V or 115V supplied from grid, thereby, from phase to phase totaling to 220v or 230v. I have seen it in US. Please do not misguide. 120V/240V is nominal! Research nominal!

>220V single phase service doesn't exist in the US. It's
>either 120V/240V (2-pole generator) or household-power
>120V/208V (3-pole generator with 3-phase).
>there is no 110V, 115V, 220V nor 230V in the US.
>230V/ 400V is Europe.
>
>>What about the reverse? Can you power something rated for
>>208v with 220v single phase service?
 
B
120 - 240 single phase power is common in the US. 120 208 3 phase power is also common. 277 480 3 phase power is also common. Chances are you will get one of these three power sources if you are in the u.s. there are some three phase Delta sources 240 and 480, and an occasional Corner grounded system. There are also some three phase 240 systems where one phase is Center tapped so you can get 120 from line to Center for lighting and receptacles.
 
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