 Phil you are smoking dope! Get out your meter and check the voltage for yourself. 240v  Delta has A to ground 120v, B to ground 240v C to ground 120v. A to B 240v, B to C 240v  and A to C 240v. 120y 208v is as follows: A to ground 120v, B to ground
120v, and C to  ground 120v. A to B 208v, B to C 208v and A to C 208.
Sorry, Brian, but you're the one on dope ... at least a little bit. All is right except the B to ground. Your WYE voltages are right. Get out your calculator and do some vector arithmetic. It works out as shown.
Here's the vector diagram in ASCII (fixed font needed to view right):
B /\ /  \ /  \ ANC
You will get the following: AB = 240 volts (30 degrees) BC = 240 volts (330 degrees) CA = 240 volts (270 degrees) NA = 120 volts (270 degrees) NC = 120 volts (90 degrees) NB = 207.8460969 (0 degrees)
Carefully draw this on some graph paper so that all 3 sides of the triangle are exactl 240 units of some unit of measure. Then measure the apex to the center of the bottom line in the same units.
That's why you can get a cheap 240 delta out of a ScottT hookup that looks like this:
B    ANC
By taking a normal single phase 240/120 volt transformer connected between two primary phases (for example 12470 > 240/120) and taking a single phase 208 volt connected phase to ground using a different phase from the first two (this getting a 90 degree vector). This is called the "teaser leg".
Adding vectors C>N (120 volts at 270 degrees) + N>B (208 volts at 0 degrees), you end up with 240 volts at 330 degrees (C>B). Literally you get 240.1332963 volts at 330.01836 degrees if you use exactly 208 volts. But if you use 120*sqrt(3) you will hit the 240 volts on the mark.
Now let's suppose some makes a mistake and uses a 240 volt transformer for the teaser instead of 208 volt. It wouldn't be that far off, and motors would probably run OK. But you will get the following under such a miswiring:
AB = 268.3281573 volts (26.5650512 degrees) BC = 268.3281573 volts (333.4349488 degrees) CA = 240 volts (270 degrees) NA = 120 volts (270 degrees) NC = 120 volts (90 degrees) NB = 240 volts (0 degrees)
Draw a horizontal line of 240 units. Then from the center of that line draw a vertical line of 240 units upward. Now measure from the apex of the vertical line to either end of the horizontal line. You get about 268.3.
  wrote in message news: snippedforprivacy@news1.newsguy.com...  On Wed, 9 Jun 2004 06:21:56 0500 Brian wrote:    240v Highleg delta is A phase 120v to ground, B phase is 240v to ground and C phase is   120v to ground. All phase to phase voltage is 240v. I have never seen or heard of  240v   Wye system here is the U.S. But to answer your question the buss bars will handle   voltage above 120v.   I disagree with you on the B phase. Draw the triangle with 240 volt  sides, horizontal on the bottom. Now put a ground dot at the center  on the bottom (not at a corner). The B leg voltage is from the apex  to the ground. Since we know that the side of a right triangle is  the square root of the sum of the square of the two right sides, we  can verify that my voltages are right.   120 volts * sqrt(3) = (approx) 207.8460969 volts   120 ^ 2 = 14400  207.8460969 ^ 2 = 43199.99999656418961 = (approx) 43200  14400 + 43200 = 57600  sqrt(57600) = 240   240 / sqrt(3) = (approx) 138.5640646 = (roughly) 139   Assuming A and C phases can handle 139 volts, then 240Y/139 provides  a safer configuration of power that should be able to run all 240 volt  three phase motors. This voltage can be produced by many three phase  generators, derived via transformers (such as with a 277/139 split  phase secondary), and I've even found it offered by at least one power  company:  
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  The issue is whether it can be used with circuit panels rated for  240 delta, or whether one has to upgrade the panel where the next  available is for 480Y/277 (double that of 240Y/139).   A panel rated for 240 delta certainly must have insulation rated for a  minimum of:   240 volts between bus bars  208 volts between bus bar B and ground/chassis  120 volts between bus bars A or C and ground/chassis   But 240Y/139 raises the voltage slightly for A and C, and a panel  that is designed to the bare minimum for 240 delta could actually  be exceeded with 240Y/139 by applying 139 volts on the phases, and  exceed the possible 120 volt rating to ground of A and C.        Phil Howard KA9WGN 
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   (first name) at ipal.net 
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