# About 3-phase AC

Discussion in 'Electronic Basics' started by Jack// ani, Apr 7, 2005.

1. ### Jack// aniGuest

Hi there,

In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
phase to phase voltage 220? I know phase difference between any two
phases differ by 120 degree, so they should add up to give something
less than 220V! It should sum up to give 220V if the phase difference
were 0 degree or 360degree!

Thanks

Jack// ani, Apr 7, 2005

2. ### Larry BrasfieldGuest

"Jack// ani" <> wrote in message
news:...
> Hi there,

Hi.
> In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
> phase to phase voltage 220? I know phase difference between any two
> phases differ by 120 degree, so they should add up to give something
> less than 220V!

The mathematical impossibility you ask about does not
happen. What makes you think it does?

> It should sum up to give 220V if the phase difference
> were 0 degree or 360degree!

Many people do not distinguish 0 and 360 degrees
for continuous sinusoids.

--
--Larry Brasfield
email:
Above views may belong only to me.

Larry Brasfield, Apr 7, 2005

3. ### Lord GarthGuest

"Jack// ani" <> wrote in message
news:...
> Hi there,
>
> In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
> phase to phase voltage 220? I know phase difference between any two
> phases differ by 120 degree, so they should add up to give something
> less than 220V! It should sum up to give 220V if the phase difference
> were 0 degree or 360degree!
>
> Thanks
>

The phase to phase voltage in the USA is 207 VAC which is phase to ground x
1.732
120 x 1.732 = 207.84 You can find this voltage supply running the light in
many
buildings.

Houses get one 240 volt phase which is transformed to provide 2 outputs of
120 volts
that are 180 degrees apart, with respect to ground.

Three 240 volt phases implies the phase to phase voltage from this circuit
is 415.68 volts.

Lord Garth, Apr 7, 2005
4. ### Andrew HolmeGuest

Jack// ani wrote:
> Hi there,
>
> In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
> phase to phase voltage 220? I know phase difference between any two
> phases differ by 120 degree, so they should add up to give something
> less than 220V! It should sum up to give 220V if the phase difference
> were 0 degree or 360degree!
>
> Thanks

They would *add* to give 110V, but I suspect you're talking about the
potential difference between phases. Using the cosine rule, the PD between
phases is:

sqrt(110*110 + 110*110 - 2*110*110*cos(120)) = 190.5

Andrew Holme, Apr 7, 2005
5. ### Jack// aniGuest

I think you got something wrong, or I didn't expressed it correclty!
Say you have two AC sources of 110V, now if I put them in series they
should add up to give 220V if their instantaneous phases are same(0 or
360) or if they are 180 phase out they should sum up to zero. I think
these two AC sources are just like two phases of 3-phase AC supply
which are 120degree phase apart. And they should give a voltage less
than 220V when summed up.

Any Help...Thanks

Jack// ani, Apr 7, 2005
6. ### Larry BrasfieldGuest

"Jack// ani" <> wrote in message
news:...
>I think you got something wrong, or I didn't expressed it correclty!

I'll go with that set of alternatives.

> Say you have two AC sources of 110V, now if I put them in series they
> should add up to give 220V if their instantaneous phases are same(0 or
> 360) or if they are 180 phase out they should sum up to zero. I think
> these two AC sources are just like two phases of 3-phase AC supply
> which are 120degree phase apart. And they should give a voltage less
> than 220V when summed up.

Your above statements are consistent with phasor
arithmetic as I understand it, as long as "just like",
"less than", and "summed up" are interpreted in a
way most favorable to your understanding.

> Any Help...Thanks

You'll need to describe your issue more specifically
to get any help with it, I believe.

--
--Larry Brasfield
email:
Above views may belong only to me.

Larry Brasfield, Apr 7, 2005
7. ### svetoslav belchevGuest

Here in bulgaria a 3 phase AC is 220 V phase-ground and 380 V phase-prase

svetoslav belchev, Apr 7, 2005
8. ### Peter BennettGuest

On 7 Apr 2005 11:03:49 -0700, "Jack// ani" <>
wrote:

>Hi there,
>
>In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
>phase to phase voltage 220? I know phase difference between any two
>phases differ by 120 degree, so they should add up to give something
>less than 220V! It should sum up to give 220V if the phase difference
>were 0 degree or 360degree!
>
>Thanks

In North America, line voltage is 120 volts to ground. With three
phase power this gives you 208 volts between phases.

If the phase difference between two circuits is 0 degrees, you will
measure zero volts between them.

In normal residential wiring, we have two wires that are 180 degrees
out of phase - this gives 240 volts between "phases" (some people
object to using the term "phase in this situation...)

Although the electrical distribution system as a whole is three-phase,
individual homes are fed from the secondary of a single phase
transformer. The secondary of the transformer is center-tapped, with
the tap grounded to form the neutral conductor. There is 240 volts
between the ends of the secondary.

--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq

Peter Bennett, Apr 7, 2005
9. ### Bob EldredGuest

"Jack// ani" <> wrote in message
news:...
> Hi there,
>
> In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
> phase to phase voltage 220? I know phase difference between any two
> phases differ by 120 degree, so they should add up to give something
> less than 220V! It should sum up to give 220V if the phase difference
> were 0 degree or 360degree!
>
> Thanks

It's a very simple geometric relationship. If two lines or vectors are 120
degrees apart and are of equal length from their common, crossing end, the
distance between the tips of the lines is 2*sin (120/2). = 2*0.866 = 1.732.
Now, if the line lengths represents 120 volts from the center or crossing
point to the tip, the tips must be 120 * 1.732 apart = 207.8 Volts. OK
class, for homework, prove the geometric relationship. BTW it can be proven
without trigonometry.
Bob

Bob Eldred, Apr 9, 2005
10. ### John LarkinGuest

On 7 Apr 2005 11:03:49 -0700, "Jack// ani" <>
wrote:

>Hi there,
>
>In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
>phase to phase voltage 220? I know phase difference between any two
>phases differ by 120 degree, so they should add up to give something
>less than 220V! It should sum up to give 220V if the phase difference
>were 0 degree or 360degree!
>
>Thanks

One common but bizarre US wiring practice is to have a 240 volt
line-to-line delta three-phase system in which one side of the
triangle is center-tapped and is neutral. So 120 single-phase is
available for regular outlets, 240 single-phase is available for
things that need it, and 240 line-to-line is available for three phase
loads. That's fairly common in small commercial buildings. The leg
opposite the neutral is call the "bitch leg" or the "stinger."

John

John Larkin, Apr 9, 2005
11. ### Bob EldredGuest

"John Larkin" <> wrote in
message news:...
> On 7 Apr 2005 11:03:49 -0700, "Jack// ani" <>
> wrote:
>
> >Hi there,
> >
> >In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
> >phase to phase voltage 220? I know phase difference between any two
> >phases differ by 120 degree, so they should add up to give something
> >less than 220V! It should sum up to give 220V if the phase difference
> >were 0 degree or 360degree!
> >
> >Thanks

>
>
> One common but bizarre US wiring practice is to have a 240 volt
> line-to-line delta three-phase system in which one side of the
> triangle is center-tapped and is neutral. So 120 single-phase is
> available for regular outlets, 240 single-phase is available for
> things that need it, and 240 line-to-line is available for three phase
> loads. That's fairly common in small commercial buildings. The leg
> opposite the neutral is call the "bitch leg" or the "stinger."
>
> John

I can't see how that can be a delta. I think what you have described is a
six phase "Y", center neutral as usual. It's 120 Volts out any leg and 240
Volt center tapped any leg to it's stinger. And, 208 Volts leg to leg. It's
also 120 Volts from any leg to the adjacent stinger. It's not all that
bizarre and can be created from any three phase system with a transformer.
Bob

Bob Eldred, Apr 9, 2005
12. ### John LarkinGuest

On Sat, 09 Apr 2005 03:43:44 GMT, "Bob Eldred" <>
wrote:

>
>"John Larkin" <> wrote in
>message news:...
>> On 7 Apr 2005 11:03:49 -0700, "Jack// ani" <>
>> wrote:
>>
>> >Hi there,
>> >
>> >In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
>> >phase to phase voltage 220? I know phase difference between any two
>> >phases differ by 120 degree, so they should add up to give something
>> >less than 220V! It should sum up to give 220V if the phase difference
>> >were 0 degree or 360degree!
>> >
>> >Thanks

>>
>>
>> One common but bizarre US wiring practice is to have a 240 volt
>> line-to-line delta three-phase system in which one side of the
>> triangle is center-tapped and is neutral. So 120 single-phase is
>> available for regular outlets, 240 single-phase is available for
>> things that need it, and 240 line-to-line is available for three phase
>> loads. That's fairly common in small commercial buildings. The leg
>> opposite the neutral is call the "bitch leg" or the "stinger."
>>
>> John

>
>I can't see how that can be a delta. I think what you have described is a
>six phase "Y", center neutral as usual. It's 120 Volts out any leg and 240
>Volt center tapped any leg to it's stinger. And, 208 Volts leg to leg. It's
>also 120 Volts from any leg to the adjacent stinger. It's not all that
>bizarre and can be created from any three phase system with a transformer.
>Bob
>

What I described is this:

C
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ (gnd) \
/ | \
A------------N------------B
| | |
| | |
120 N 120

John

John Larkin, Apr 9, 2005
13. ### Bob EldredGuest

"John Larkin" <> wrote in
message news...
> On Sat, 09 Apr 2005 03:43:44 GMT, "Bob Eldred" <>
> wrote:
>
> >
> >"John Larkin" <> wrote in
> >message news:...
> >> On 7 Apr 2005 11:03:49 -0700, "Jack// ani" <>
> >> wrote:
> >>
> >> >Hi there,
> >> >
> >> >In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
> >> >phase to phase voltage 220? I know phase difference between any two
> >> >phases differ by 120 degree, so they should add up to give something
> >> >less than 220V! It should sum up to give 220V if the phase difference
> >> >were 0 degree or 360degree!
> >> >
> >> >Thanks
> >>
> >>
> >> One common but bizarre US wiring practice is to have a 240 volt
> >> line-to-line delta three-phase system in which one side of the
> >> triangle is center-tapped and is neutral. So 120 single-phase is
> >> available for regular outlets, 240 single-phase is available for
> >> things that need it, and 240 line-to-line is available for three phase
> >> loads. That's fairly common in small commercial buildings. The leg
> >> opposite the neutral is call the "bitch leg" or the "stinger."
> >>
> >> John

> >
> >I can't see how that can be a delta. I think what you have described is a
> >six phase "Y", center neutral as usual. It's 120 Volts out any leg and

240
> >Volt center tapped any leg to it's stinger. And, 208 Volts leg to leg.

It's
> >also 120 Volts from any leg to the adjacent stinger. It's not all that
> >bizarre and can be created from any three phase system with a

transformer.
> >Bob
> >

>
>
> What I described is this:
>
>
> C
> / \
> / \
> / \
> / \
> / \
> / \
> / \
> / \
> / \
> / \
> / (gnd) \
> / | \
> A------------N------------B
> | | |
> | | |
> 120 N 120
>
>
>
> John

Why would anybody do that? What is the voltage from A to C? A to N?, What
is the relation of N to ground. Clearly this kind of a bastard connection
would be prone to gross unbalance or to parasitic voltages on the neutral.
If its 240V leg to leg, with N in the center of one leg, what is N to B for?
What is the voltage B to C? Furthermore if its 240 Volts three phase on all
legs, what equipment uses it, most are 208? Since 120 Volts is only
available from one leg with a neutral how is power distributed in a building
say to lighting or to other 120 Volt circuits maintaining some semblance of
balance between the phases. I'm not saying you have never seen this but I
never have and it can't be very common.
Bob

Bob Eldred, Apr 9, 2005
14. ### John LarkinGuest

On Sat, 09 Apr 2005 18:34:02 GMT, "Bob Eldred" <>
wrote:

>
>"John Larkin" <> wrote in
>message news...
>> On Sat, 09 Apr 2005 03:43:44 GMT, "Bob Eldred" <>
>> wrote:
>>
>> >
>> >"John Larkin" <> wrote in
>> >message news:...
>> >> On 7 Apr 2005 11:03:49 -0700, "Jack// ani" <>
>> >> wrote:
>> >>
>> >> >Hi there,
>> >> >
>> >> >In 3-phase AC wiring, if phase to neutral voltage is 110V, then why is
>> >> >phase to phase voltage 220? I know phase difference between any two
>> >> >phases differ by 120 degree, so they should add up to give something
>> >> >less than 220V! It should sum up to give 220V if the phase difference
>> >> >were 0 degree or 360degree!
>> >> >
>> >> >Thanks
>> >>
>> >>
>> >> One common but bizarre US wiring practice is to have a 240 volt
>> >> line-to-line delta three-phase system in which one side of the
>> >> triangle is center-tapped and is neutral. So 120 single-phase is
>> >> available for regular outlets, 240 single-phase is available for
>> >> things that need it, and 240 line-to-line is available for three phase
>> >> loads. That's fairly common in small commercial buildings. The leg
>> >> opposite the neutral is call the "bitch leg" or the "stinger."
>> >>
>> >> John
>> >
>> >I can't see how that can be a delta. I think what you have described is a
>> >six phase "Y", center neutral as usual. It's 120 Volts out any leg and

>240
>> >Volt center tapped any leg to it's stinger. And, 208 Volts leg to leg.

>It's
>> >also 120 Volts from any leg to the adjacent stinger. It's not all that
>> >bizarre and can be created from any three phase system with a

>transformer.
>> >Bob
>> >

>>
>>
>> What I described is this:
>>
>>
>> C
>> / \
>> / \
>> / \
>> / \
>> / \
>> / \
>> / \
>> / \
>> / \
>> / \
>> / (gnd) \
>> / | \
>> A------------N------------B
>> | | |
>> | | |
>> 120 N 120
>>
>>
>>
>> John

>
>
>Why would anybody do that? What is the voltage from A to C? A to N?, What
>is the relation of N to ground. Clearly this kind of a bastard connection
>would be prone to gross unbalance or to parasitic voltages on the neutral.
>If its 240V leg to leg, with N in the center of one leg, what is N to B for?
>What is the voltage B to C? Furthermore if its 240 Volts three phase on all
>legs, what equipment uses it, most are 208? Since 120 Volts is only
>available from one leg with a neutral how is power distributed in a building
>say to lighting or to other 120 Volt circuits maintaining some semblance of
>balance between the phases. I'm not saying you have never seen this but I
>never have and it can't be very common.
>Bob
>

Google "three phase stinger" or some such.

John

John Larkin, Apr 9, 2005
15. ### Guest

Bob Eldred wrote:
> "John Larkin" <> wrote

in
> message news...
> > On Sat, 09 Apr 2005 03:43:44 GMT, "Bob Eldred"

<>
> > wrote:
> >
> > >
> > >"John Larkin" <>

wrote in
> > >message news:...
> > >> On 7 Apr 2005 11:03:49 -0700, "Jack// ani"

<>
> > >> wrote:
> > >>
> > >> >Hi there,
> > >> >
> > >> >In 3-phase AC wiring, if phase to neutral voltage is 110V, then

why is
> > >> >phase to phase voltage 220? I know phase difference between any

two
> > >> >phases differ by 120 degree, so they should add up to give

something
> > >> >less than 220V! It should sum up to give 220V if the phase

difference
> > >> >were 0 degree or 360degree!
> > >> >
> > >> >Thanks
> > >>
> > >>
> > >> One common but bizarre US wiring practice is to have a 240 volt
> > >> line-to-line delta three-phase system in which one side of the
> > >> triangle is center-tapped and is neutral. So 120 single-phase is
> > >> available for regular outlets, 240 single-phase is available for
> > >> things that need it, and 240 line-to-line is available for three

phase
> > >> loads. That's fairly common in small commercial buildings. The

leg
> > >> opposite the neutral is call the "bitch leg" or the "stinger."
> > >>
> > >> John
> > >
> > >I can't see how that can be a delta. I think what you have

described is a
> > >six phase "Y", center neutral as usual. It's 120 Volts out any leg

and
> 240
> > >Volt center tapped any leg to it's stinger. And, 208 Volts leg to

leg.
> It's
> > >also 120 Volts from any leg to the adjacent stinger. It's not all

that
> > >bizarre and can be created from any three phase system with a

> transformer.
> > >Bob
> > >

> >
> >
> > What I described is this:
> >
> >
> > C
> > / \
> > / \
> > / \
> > / \
> > / \
> > / \
> > / \
> > / \
> > / \
> > / \
> > / (gnd) \
> > / | \
> > A------------N------------B
> > | | |
> > | | |
> > 120 N 120
> >
> >
> >
> > John

>
>
> Why would anybody do that? What is the voltage from A to C? A to N?,

What
> is the relation of N to ground. Clearly this kind of a bastard

connection
> would be prone to gross unbalance or to parasitic voltages on the

neutral.
> If its 240V leg to leg, with N in the center of one leg, what is N to

B for?
> What is the voltage B to C? Furthermore if its 240 Volts three phase

on all
> legs, what equipment uses it, most are 208? Since 120 Volts is only
> available from one leg with a neutral how is power distributed in a

building
> say to lighting or to other 120 Volt circuits maintaining some

semblance of
> balance between the phases. I'm not saying you have never seen this

but I
> never have and it can't be very common.
> Bob

It's still common in the US where houses are mixed with small motor
installations. That unexpected 208-to-neutral is(was) a problem on
water-well controls when you needed 120v for the control-circuit.

, Apr 10, 2005
16. ### Lord GarthGuest

<> wrote in message
news:...
> Bob Eldred wrote:

<snip>
> It's still common in the US where houses are mixed with small motor
> installations. That unexpected 208-to-neutral is(was) a problem on
> water-well controls when you needed 120v for the control-circuit.
>

Around here, all delta circuits are being replaced with a wye configuration.
The utility has standardized on this...then all the other power utilities
came
on the scene so who knows !

Lord Garth, Apr 10, 2005
17. ### Bob EldredGuest

"Lord Garth" <> wrote in message
news:iZ16e.393\$...
>
> <> wrote in message
> news:...
> > Bob Eldred wrote:

> <snip>
> > It's still common in the US where houses are mixed with small motor
> > installations. That unexpected 208-to-neutral is(was) a problem on
> > water-well controls when you needed 120v for the control-circuit.
> > WAde H
> >

>
> Around here, all delta circuits are being replaced with a wye

configuration.
> The utility has standardized on this...then all the other power utilities
> came
> on the scene so who knows !

Well, that certainly makes more sense than some sort of a nutty asymetrical
grounding scheme. Oh well, based on the above comments, I guess anything is
possible. What does the NEC have to say about it?
Bob

Bob Eldred, Apr 10, 2005
18. ### Don KellyGuest

"Jack// ani" <> wrote in message
news:...
> I think you got something wrong, or I didn't expressed it correclty!
> Say you have two AC sources of 110V, now if I put them in series they
> should add up to give 220V if their instantaneous phases are same(0 or
> 360) or if they are 180 phase out they should sum up to zero. I think
> these two AC sources are just like two phases of 3-phase AC supply
> which are 120degree phase apart. And they should give a voltage less
> than 220V when summed up.
>
> Any Help...Thanks

Your two single phase 110 sources in series will give 220V or 0 depending on
connection. This is the Edison or 3 wire single phase system in the 220V
case (and something useless in the other case) which is a common North
American configuration. In Europe, where it is not used, it is called a 2
phase system and if one defines an phase system as having n voltages to
neutralThere are two basic forms of a 3 phase connection -star in which
there is a common neutral or delta where there is no neutral. .You mention a
voltage of 110V to neutral so the corresponding voltage between lines is
110*root(3)=190V.

In a star connected 3 phase system the phase and line currents are the same
but line to line voltages are greater than phase to neutral voltages by the
factor of root(3). In a delta the phase and line to line voltages are the
same but the line (external) currents are root(3) times the phase (internal)
currents.

There are advantages and disadvantages to both and advantages for 3 phase
over single phase (2 or 3 wire), particularly in rotating machines and
transformers.
--
Don Kelly

remove the urine to answer

Don Kelly, Apr 12, 2005