On Sat, 04 Mar 2017 01:18:19 -0500, wrote:

On Sat, 04 Mar 2017 00:02:06 -0500, wrote:

On Fri, 3 Mar 2017 18:37:52 -0600, Dean Hoffman
wrote:

On 3/3/17 4:28 PM, wrote:

There is no "phase issue" at all. There is no such thing as "two
phase" power, at least not in common North American use. All 120
volt power in north american distribution systems is derived from
center tapped 240 volt single phase transformers except in a 3 phase
distribution system, where you get 120 and 208 (120 across 1 phase,
and 208 across 2 phases of the 3 phase supply).

The REAs in rural Nebraska also supply three phase power to
irrigation well motors. I've seen center tap delta which is basically
double what you referenced. There is the Y configuration, 277 volts
each line to ground. Lastly is the corner ground delta. Two lines read
480 to
ground, the third line reads 0 to ground. All of those read 480 line
to line.
Some grain bin drying systems are wired with the three phase you
mentioned.
That lets the electricians use common 120 volt controls. There is also
enough
power with the three phase to run drying fans.

I have also seen 240v 3p corner delta, usually feeding sewer lift
pumps. It is pretty strange the first time you see it because it is 3
phase with only 2 ungrounded conductors so it looks like single phase.
(2 black wires and a white on a 2 pole breaker)

With 3 phase motors? Requires 4 wires for a 3 phase motor on corner
delta. Sounds more like single phase 208. - because theree are
generally only 2 ungrounded wires in a corner delta (which is no
longer allowed, to the best of my knowlege, in Ontario) - and with
corner delta 3 phase you have no 120 without a transformer - and
generally no center-tapped transformer is used (which is generally why
grounded delta was used - to avoid the requirement for a more
expensive center tapped transformer) Means you can't use a 240 device
that has 120 volt controls without installing a "control transformer"
on each device.to supply the required 120 volts.

They used corner delta because the only load is the motor and a 240v
MCC. There is no 120 available and it is not needed. The 4 wires are 2
hots, one neutral (another phase) and the grounding conductor. It
looks visually exactly like 120/240 single phase except that the
"neutral" is actually tied to the 3d phase, not the center tap of a
transformer. In fact they did it with just 2 transformers similar to
the way they do center tapped delta vee. (red leg delta)
The advantage of corner delta to the installer is they can use cheaper
2 pole switch gear. The only added requirement is everything needs to
be 240v rated (delta rated breakers)