| 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:

http://www.cityofseattle.net/light/contractors/resc/resc.pdf
http://www.cityofseattle.net/Light/engstd/Docs/ConStd/u977.pdf

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 | http://linuxhomepage.com/ http://ham.org/ |

Click to see the full signature.