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Data Tech/Apprentice.
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My tradesman couldnt answer my question today.

"If each phase is 230v how come its 400v across phases?"
 

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My tradesman couldnt answer my question today.

"If each phase is 230v how come its 400v across phases?"
400/1.73=231.

The phases are not 180 degrees apart they are only 120 degrees apart that is where the 'lost voltage is'

Here it is 208Y/120 or 480Y/277 in Canadah they use 600Y/347.
 

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Not sure what that means, I dont go to school until next year. Im eager to learn and have been on every switchgear changeover since Ive been at this company.
 

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My tradesman couldnt answer my question today.

"If each phase is 230v how come its 400v across phases?"
Semantics.

"If each phase is 230..." Only as measured from line to Neutral

"... how come its 400v across phases?" Only as measured Phase to Phase.

Apples and Oranges.

Well, actually Apples and Crabapples might be a better analogy.
 

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Semantics.

"If each phase is 230..." Only as measured from line to Neutral

"... how come its 400v across phases?" Only as measured Phase to Phase.

Apples and Oranges.

Well, actually Apples and Crabapples might be a better analogy.
I kind of understand that now, my question was like why theres 48v dc on the phoneline in the front and 230v on each phase, haha.
 

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In a 3 phase system, the line-neutral voltage is always the sqrt(3) of the line-line voltage. There is a mathematical proof for this involving vectors and trig identities. For all you care, just remember (sqrt3) ~= 1.73.

480/1.73 = 277
208/1.73 = 120
400/1.73 = 230

That's where it comes from. In Canada, the majority of our systems are either 208v or 600v 3 phase.
 

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In a three phase system each of your line to neutral voltage vectors are offset by 120 degrees. This means if you measure the measure the voltage between phases it will always be 1.73 times larger than your phase to neutral voltage. When you start learning about star and delta configurations at tafe and the difference between phase voltage/current and line voltage/current it will all fall into place.

All you need to know at the moment is that your phase to phase voltage will always be 1.73 times larger than your phase to neutral voltage.

This picture might help you a little bit. The blue lines are your phase to neutral voltage and red lines are your phase to phase voltages.
 

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My tradesman couldnt answer my question today.

"If each phase is 230v how come its 400v across phases?"
Pick a spot in a field and drive a stake, call it "A", walk 231 paces and drive another stake and call it "X", now turn 120 degrees and walk 231 paces drive another stake and call it "B", now walking in a straight line count the paces between "A" and "B"

Roger
 

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Donuts > Fried Eggs
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I posted this in another thread, it needs some refinement, but hopefully it gets the idea across:
This is what the sine waves look like for a three-phase system (the gray line is neutral, 0 volts):


Watch a dot on any phase. When one of the phases is at the peak on the wave (maximum voltage) you can see that the other two phases are always gonna be at lower positions (lower voltages).

That is because of how they are generated: When the field on the generator has maximum influence over the winding in "A" phase and is generating the most potential in that winding, it has less of an influence over "B" and "C". And that's true for the other ones as well, when each winding is at maximum voltage, the others are at less potential. These windings are spaced evenly apart within the generator so this peak influence on each on occurs 120° out of phase (360° ÷ 3).

With a three-phase transformer, the windings are also spaced 120° apart, so they mimic the voltages present on the generator.

That means you are measuring peak L-N voltage on "B" phase, the L-N voltage at that same time on "A" or "C" phase are not at their peaks:

("A" and "C" are actually both the same position at that red dot.)

So even though the RMS voltage on any one phase to neutral is 120V, when you measure across them you're not adding 120V+120V because the actual RMS voltages at any single time are much closer to 120V+88V or 208V.
 

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yes, but I left it out because it's not as common. In my area anyhow. Almost everything is 600/347
I've wondered why we (states) settled on 480/277. The distribution equipment is rated 600, the wire is rated 600. Seems it costs more copper for the same kva at 480/277
 
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