# Calculating 3 phase AC motor HP

| I believe I've given every piece of information explained to me.
You might not have been given the information in the correct context.
Sometimes an electrician trying to simplify things for non-electricians changes the perspective in a way that loses or distorts information.
| If the system is a 'corner ground', how does the third phase come into | play?
In a typical (North American) home single phase wiring, there are 4 wires. One is the grounding wire that does not carry current normally. The other three consist of a grounded conductor that is also the neutral conductor and two phase wires at 180 degree phase angles. If you measure between the neutral and the grounding wire, you should get 0 volts or very near to that.
A delta system can ungrounded, or grounded two ways. One way of grounding is to tap the center of one winding (between 2 phases) and ground there. The third phase that was not part of that tapped winding then has a higher voltage relative to the ground, compared to the other two. That phase is termed the high leg, or wild leg, or bastard leg. I've only heard of it used for 240 volt delta because it provides a means to get 120 volts for lights and stuff. The bastard leg in that case is 208 volts. The other way of grounding a delta system is to ground one regular phase. That gives you full voltage relative to ground on each of the other phases. But on the grounded phase, relative to ground, of course you get 0 volts.
You can also get the effect of a delta system from transformers wired in a WYE configuration, by simply ignoring the neutral, even though the system would typically be grounded at the neutral. For example a motor designed to be run on a 240 volt delta system could be run on a 240Y/139 volt WYE system (just don't connect the neutral to the motor).
The scenario you describe just doesn't match up exactly to anything known. If two wires have ZERO volts between them, then they are at the same potential. Then the third wire, which has voltage between it and either of the other two, would have to have these voltages in the SAME phase angle. Then you don't have three phase at all.
One small change in the information, changing how the voltages measurements are taken, so each wire is measured relative to ground (the 4th safety wire), easily makes this fit a corner-grounded (one of the phases is a corner of a delta) scenario. Note that such a system only needs two pole breakers, not three pole breakers, provided the breakers are rated per pole at the full system voltage.
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