# Delta / Wye 3 phase 240 VAC question.



## ndekens (Apr 4, 2008)

Well this question is actually work related and since I havn't come across this issue before I thought I would ask hear.

I have a small pump station hooked up to a 3 phase 240 VAC feed. On the incoming legs I get Phase to Ground voltages of 122VAC for Phase A &amp; B but on C I get 212VAC! This is the confusing part...My local guy says the Power companies XFMR is wired Delta EL = EP.....not the case (Right?) Also when metered phase to phase I get 244VAC across the board.

So any opinions on the reason for the high leg? My guess is the power company has something haywire.


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## Flyer_PE (Apr 4, 2008)

Your transformer is 3-phase delta wired. One of the phases has a grounded center tap. For the phase with the grounded center tap, you will read 120V to ground on either side. Measured from ground, the voltage to the third phase will be a nominal 208 Vac.

Hope I'm explaining this properly.

Jim


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## ndekens (Apr 4, 2008)

IFR_Pilot said:


> Your transformer is 3-phase delta wired. One of the phases has a grounded center tap. For the phase with the grounded center tap, you will read 120V to ground on either side. Measured from ground, the voltage to the third phase will be a nominal 208 Vac.
> Hope I'm explaining this properly.
> 
> Jim


Thanks! I got it now...First time I ran into this. Im use to 480 3 phase....not this 240 stuff.


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## clemente (Apr 4, 2008)

is that middle phase orange in color?


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## clemente (Apr 4, 2008)

is that middle phase orange in color?


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## adr (Apr 4, 2008)

Info at siemens.com:

http://www.sea.siemens.com/step/templates/...mason?pan:3:2:3


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## Art (Apr 5, 2008)

draw the phasor diagram...

a delta or triangle with 240 per side...base on the bottom

then a ground splitting the bottom...

the leg on either side of the gnd is 1/2 240 = 120 or cos 60 x 240 = 120

the opposite or high leg on top (the 'point') to ground is cos (1/2 x 60 deg) x 240 = cos 30 x 240 = 207.85 or 208


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