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05-04-2012, 12:08 AM   #1
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## line and phase voltage

sir
i have seen on this site------------------------------------------------------------120/240 for houses: 120 is line to ground, 240 is line to line

so got the point from this point that we have three phase connection so
120 is phase voltage and 240 is line voltage

but line voltage is=squareroot of 3 *phase voltage and (240 is not equal to sqroot of 3*120)

Last edited by Gary in WA; 05-04-2012 at 01:08 AM. Reason: Removed link as per forum rules.

05-04-2012, 01:17 AM   #2
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WOW. Thats quite a theory.

The first sentence is OK.

The rest is not.

Didn't come from here.

05-04-2012, 02:28 AM   #3
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Quote:
 Originally Posted by ashish walia sir i have seen on this site------------------------------------------------------------120/240 for houses: 120 is line to ground, 240 is line to line so got the point from this point that we have three phase connection so 120 is phase voltage and 240 is line voltage but line voltage is=squareroot of 3 *phase voltage and (240 is not equal to sqroot of 3*120) please send the answer on --------- as soon as possible
Residential 240 is not 3 phase...it's single phase.....with a center tap neutral reference.

This picture might help illustrate how it works.

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05-04-2012, 06:52 AM   #4

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Quote:
 Originally Posted by ashish walia please send the answer on --------- as soon as possible
Ummmmmm......NOPE!

A) I don't answer forum posts privately. That is completely counter to what these forums are all about.

B) I don't do home work for other people.
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Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.

 The Following 2 Users Say Thank You to Speedy Petey For This Useful Post: gregzoll (05-04-2012), user1007 (05-04-2012)
05-04-2012, 07:44 AM   #5
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Quote:
 Originally Posted by ashish walia sir i have seen (snip) 120/240 for houses: 120 is line to ground, 240 is line to line so got the point from this point that we have three phase connection so 120 is phase voltage and 240 is line voltage but line voltage is=squareroot of 3 *phase voltage and (240 is not equal to sqroot of 3*120) (snip)
If you indeed had two legs of a symmetric neutral (wye; star; etoile) 3 phase system as your service then hot to hot would measure about 208 volts.

Once in awhile, residences in (upper floors of?) a commercial building or in a primarily commercial district may have 120/208 volt service taken from 3 phase pole transformers. In general, 120/240 rated and 240 volt only rated equipment may not be connected to 120/208 volt systems and vice versa. Some equipment is rated for both voltages.

A 120/240 volt 3 phase system (it's always 3 phase delta) provides 120/240 volt single phase power per the diagram above and a third hot wire is for 240 volt only 3 phase equipment such as machinery,

Even in a three phase system of any kind, if you take power from any two terminals (hot and hot, or hot and neutral) you will have a single phase source.
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Last edited by AllanJ; 05-04-2012 at 07:59 AM.

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05-04-2012, 08:53 AM   #6
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Quote:
 Originally Posted by ashish walia sir i have seen on this site------------------------------------------------------------120/240 for houses: 120 is line to ground, 240 is line to line so got the point from this point that we have three phase connection so 120 is phase voltage and 240 is line voltage but line voltage is=squareroot of 3 *phase voltage and (240 is not equal to sqroot of 3*120) please send the answer on --------- as soon as possible
Why do you ask and where do you live?

 05-04-2012, 08:56 AM #7 Licensed Electrician     Join Date: Mar 2012 Location: SE Wisconsin Posts: 4,352 Rewards Points: 2,006 .....
05-04-2012, 07:26 PM   #8
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Quote:
 Originally Posted by ashish walia sir i have seen on this site------------------------------------------------------------120/240 for houses: 120 is line to ground, 240 is line to line so got the point from this point that we have three phase connection so 120 is phase voltage and 240 is line voltage but line voltage is=squareroot of 3 *phase voltage and (240 is not equal to sqroot of 3*120) please send the answer on --------- as soon as possible

If your hot to neutral is measured at 120v !
Then the voltage across two hots depends on two things !
If it originates from a split supply then it will be 240v !
But if it is a measur ment from two phases,
of a three phase supply,
then it will not be 240v! but more like 220v,
Because the phase difference in a three phase system
would be only 120 degrees,
Where as in a split supply it would be 180 degrees.

If you are tring to understand electrical systems,
Then you must understand the difference between
split systems and three phase systems !

05-04-2012, 09:28 PM   #9
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Quote:
 Originally Posted by k_buz .....
My take too.
Opening with "sir" also points to this tread being started in a foreign country
Let's see how long before ashish has a follow-up post

 The Following User Says Thank You to a7ecorsair For This Useful Post: user1007 (05-04-2012)
05-04-2012, 09:32 PM   #10

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Quote:
 Originally Posted by a7ecorsair Let's see how long before ashish has a follow-up post
I've got a fiver that says she never returns.
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05-04-2012, 09:51 PM   #11
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Quote:
 Originally Posted by Speedy Petey I've got a fiver that says she never returns.
I will take the bet if you tell me if we are playing \$5 with US dollars, Irish pound notes, or Euros. I need 3:1 at least though to bank the bet.

We in the US love our electrical system. The fact that a mean or wayward squirrel can take out entire sections of the country does not 1-2 or even 3 phase us at all?

My fave 3-phase equipment is mass transportation and I love the pigeons of Philadelphia most with no claws and just balancing on nubs.

I grew up with 3-phase when it supposedly kept giant saws and things working longer.

When the OP responds again I am going to use the money I won from you, at Target or something, to buy me a 3-phase meat grinder.

 The Following User Says Thank You to user1007 For This Useful Post: Speedy Petey (05-04-2012)

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