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

A

#### Anonymous

what does it mean when something is rated 120/208V or 277/480V? What do the two numbers mean?

Help, very confused!

A

#### Anonymous

It means it is rated to operate at those two voltages.

Either 120V or 208V.

T

#### Theo

it means that the related equipment can be energized under a rated voltage from 120V (ac supply i think) up to 208V.

THEO

B

#### Bilal Janjua

I think they refer to primary and secondary voltages.

B

#### Bill Mostia

The number are for three phase systems - 120 -voltage from phase to neutral / 208 - voltage phase to phase 277 -voltage from phase to neutral / 480 - voltage phase to phase

Things that are rated are for these voltage suitable for service at these voltages.

Bill Mostia
==========================
William(Bill) L. Mostia, Jr. P.E.
Partner
exida.com
Worldwide Excellence in Dependable Automation
[email protected] (b) [email protected] (h)
www.exida.com 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

B

#### B Kaloti

120/208VAC means that power distribution is 3 phase with neutral connection (Y System). 120V represents voltage of each phase to neutral point and 208V represents voltage between any two phases.

For balance systems, line to neutral voltage is line to line voltage divided by 1.73 (Sq. root of 3). i.e 120x1.73=208V and 277x1.73=480V

A

#### Anonymous

It seems that there are 3 numbers 120VAC or the eqipment can run on 208VAC

S

#### srbelec

the first number is your L-N voltage, the second is your L-L voltage on a 3 phase system.

W

#### Wasim Ullah Khan

This is the Voltage rating commonly used in the world. Some countries have 120 V the others have approx. 240V at consumer end. These ratings are single phase. THe 277/480V is 3 Phase rating. So the appliances which bearing rating 120V/208V or 227/480V can be plugeed in both standards.

J

#### Johan Bengtsson

It is a 3-phase device (motor/heater/...)
Those devices can be connected in two different ways to the three phases.

D connection - connect each of the three parts of the device between two phases in such a way that each phase is connected to two of these devices. Feed it with a 3-phase voltage with the lower rating

----------------
| |
Phase 1 ------*---XXXX---- |
| |
------------ |
| |
Phase 2 ------*---XXXX---- |
| |
------------ |
| |
Phase 3 ------*---XXXX--------

Y connection - connect one end of each part of the device to one phase each and the remaining ends tyed torether, those ends can optionally be connected to neutral. Feed it with a 3-phase voltage witht he higher rating

Phase 1 ----------XXXX----
|
Phase 2 ----------XXXX---*
|
Phase 3 ----------XXXX---*
|
Neutral (optional) -------

Note that the higher voltage is approx equal to the lower multiplied with sqrt(3). In europe we usually have a 230/400V system by the way...

/Johan Bengtsson

Do you need education in the area of automation?
----------------------------------------
P&L, Innovation in training
Box 252, S-281 23 Hässleholm SWEDEN
Tel: +46 451 74 44 00, Fax: +46 451 898 33
E-mail: [email protected]
Internet: http://www.pol.se/

C

#### Christian Albert P.Eng.

No Problem. It means that you have a Y configuration three phases circuit. 3 phases circuits are widely used for power transmission and distribution because it's the most economical.
You can have two configurations: Y and Delta. The voltage you indicated says to an electrician that you have a Y configuration. The center of the Y is grounded and the phase to phase voltage is 208 volts or 480 Volts. The voltage from ground to each of the three phases is always the phase to phase voltage divided by the square root of 3 which is equal to 1.73. So, 208 divided by 1.73 equals 120 Volts and 480 divided by 1.73 equal 277 Volts. In Canada, we use 600 volts and the phase to ground voltage is 377 Volts. The phasing between voltage sinusoidal curves ( we say phases A, B and C) is 120 degrees. If you draw a phasor diagram with three vectors of equal amplitude (voltage) with angles of 120 degrees apart and add these vectors, you will have a result of zero. So, for a current balanced three phases circuit, the neutral current is zero. In practice, the three phases are rarely balanced.
The Y configuration needs four wires, the Delta uses only three wires. Y and Delta are used for technical consideration which are more complicated to explain.

Hope this will help.

N

I don't know what's the standard voltage in your contry but:

Sqrt(3)*120 = 208
Sqrt(3)*277 = 480

I think the first number refers to voltage between live and neutral and the second number to voltage between two lives.
Why the 277? don't know

R

#### rjs

The most popular connection on the secondary side of a 3-phase transformer is a "Y" connection. This means that one of the transformer secondary terminals (usually marked X0) is connected to earth ground and the remaining 3 terminals (usually marked X1, X2, and X3) are each of the three ouput phases.

On a 120/208 transformer secondary, the voltage measurement from the grounded X0 terminal to any of the other 3 terminals would be 120 VAC. The voltage between X1-X2-X3 in any combination would give you a measurement of 208 VAC. This is the typical connection scheme for residential power. You may also see this specified as 230/133.

On a 277/480 transformer secondary, the voltage measurement from the grounded X0 terminal to any of the other 3 terminals would be 277 VAC. The voltage between X1-X2-X3 in any combination would give you a measurement of 480 VAC. This specification is usually found in industrial or commercial applications (such as isolation transformers for variable speed drives). You may also see this specified as 460/266.

I tried to keep the above descriptions as simple as possible. If you need further details, email me at [email protected].

A

#### Anonymous

It means it will work for these two voltages i.e., a motor can be wired for either voltage. A electrical panel can be one or the other. Between to phases you would measure 208vac then one phase to netural 120vac or 480vac between phases and 277vac one phase to netural.

hope you understand

J

#### James Ingraham

277V would be a single phase of a 3-phase 480V system, so those numbers make some sense. 120 would be a single phase of 208V... but I've never heard of using 3-phase 208 volt. 220, 230, or 240 volt, sure, but 208?

Incidentally, to figure out the voltage level of a 3-phase system given the voltage of one leg, multiply by the square root of 3 (about 1.732). If you want to know the voltage level of one leg of a 3-phase system divide the 3-phase voltage by squart root of 3.

-James Ingraham
Sage Automation, Inc.

M

#### MCS

You may note that the higher number is the lower one multiplied by approx. 1.742 (sqrt of 3) - the lower number is the phase to neutral voltage, the higher is the phase-to-phase voltage. The rest is electrical theory or plane geometry.

Meir

B

Well, if you noticed that if you multiply the first number by 1.73 you get the second number. That should tell you right away that it is something to do with 'balanced three-phase' power.

Both those 'somethings' are a three phase, four wire electric distribution system. And, for example, 480V would be the phase-to-phase voltage potential (although not in phase, a whole other issue) and 277 would be the voltage between a phase conductor and the neutral, or 'grounded conductor', as the NEC likes to call it.

Encinitas, CA
USA

#### PhilCorso

Each designation refers to a 3-phase, 4-wire source of power. They are used to supply power to both 3-phase and single-phase loads. In other words in addtion to the 3-phase wires carrying current, the neutral wire can too.

For example, in the USA, the first is properly designated as 208Y/120. It describes a source having three phase-to-phase voltages (3 of the wires) that are each 208 V, while each phase-to-neutral (the 4th wire) voltage is 120 V. The second is designated 480Y/277, meaning that the phase-to-phase voltages are 480 V, and the phase-to-neutral voltage is 277 V.

By the way, the neutral wire must be connected to ground (earth) at only one location, i.e., the neutal terminal of the supply transformer.

Regards, Phil Corso, PE
Boca Raton, FL
[[email protected]]
([email protected])
{[email protected]}

N

1. There are basically two standards for AC input power supply worldwide. That is 230V in some parts of the world and 110V in some other parts.
2. 120/208V is for a 110V system basically with 120V as L to N and 208V as L to L. Similarly, for 277/480V, 277 is L to N and 480V is L to L
(V L to L = V L to N).
3. Now your question means that the equipment is expected to work either on 110V AC basic or 230VAC basic.

D

#### D. Wilson

> This is the Voltage rating commonly used in the world. Some countries have 120 V the others have approx. 240V at consumer end. These ratings are single phase. THe 277/480V is 3 Phase rating. So the appliances which bearing rating 120V/208V or 227/480V can be plugeed in both standards.

Here in Canada alot of residential services are 120/240V systems which is a single phase 120V system but two poles seperated by 180 deg therefore giving the effective Voltage of 240V for large appliances (ie Stoves, Dryers etc..)

When it comes to three phase services here you will see 120/208V or 347/600V for larger application. The odd industrial site you will see 277/480V but those are only sites where it was engineered by an American company that doesn't realise Canada uses a 347/600V system.