Working on upgrading a building's electrical service and feeders. Question is, why is 208V the standard line-to-line voltage for Y - secondary systems instead of a more logical 240V? Isnt it just a matter of the transformer's winding ratio? Can't transformer manufacturers produce any desired secondary voltage? And so why settle for a lower voltage?
Standard 208V rather than 240V
- Thread starter seviper
- Start date
circleofdown
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- Apr 6, 2025
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- 14
208V is a compromise because it's safe, standardized. I think the 240V really doesn't support wye.
black.mamba
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- Mar 25, 2025
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- 8
208V comes from the 120/208V Y setup and gives you standard 120V to neutral and 208V between phases for 3 phase loads. It's all about compatibility and sure, you could wind a transformer for 240V, but then most standard gear wouldn't match. 208V just plays nicer with everything.
To Add To Confusion:
The most common 240-Delta has a "Center Tapped" ground/neutral That is why one phase to ground on a 240 volt delta is 208 volts to ground (Yes- Confusing: 208 to ground on a 240 volt phase-to-phase)
Notice how one phase ("B" in the drawing below) has more turns of the secondary winding than the others? That is the :high leg" or the "wild leg". In our example, it is the one that is 208 to ground/neutral. In 240 volt installations, it is the one colored orange (In the United States & Canada)
Other Delta configurations are also available. Corner Grounded is common in older systems that serve large motor loads.
The 208 ground/neutral comes from a center point, thus all line-to-ground are the same voltage.
The above holds true for any voltage, but we're using 240 here based on Sevipers' question.
Fun With Physics!
Paul
The most common 240-Delta has a "Center Tapped" ground/neutral That is why one phase to ground on a 240 volt delta is 208 volts to ground (Yes- Confusing: 208 to ground on a 240 volt phase-to-phase)
Notice how one phase ("B" in the drawing below) has more turns of the secondary winding than the others? That is the :high leg" or the "wild leg". In our example, it is the one that is 208 to ground/neutral. In 240 volt installations, it is the one colored orange (In the United States & Canada)
Other Delta configurations are also available. Corner Grounded is common in older systems that serve large motor loads.
The 208 ground/neutral comes from a center point, thus all line-to-ground are the same voltage.
The above holds true for any voltage, but we're using 240 here based on Sevipers' question.
Fun With Physics!
Paul
