WOW In my professional opinion, there may possibly be a bit of mis-understanding below, let me describe the situation as I best recall and still believe:
Three Phase (3 & 4 Wire, Delta and Y) Wild Leg Open Delta
or at least how it was when I was a practicing power distribution design engineer, maybe codes or practices have changed since then SO NO WARRANTY consult the NEC and current practicing electrical engineers and electricians !!!!!!
1) Three Phase can be THREE Wire Straight Delta,,or Three Phase Four Wire Wild/Red Leg Delta,, or FOUR WIRE Y.
If THREE wire, three transformers can be CONFIGURED IN STRAIGHT DELTA, Three Hots. Such as 240 or 480 Volt Three Phase Three Wire, NO Neutral
If FOUR wire, three transformers can be CONFIGURED IN Y, Three Hots and a Neutral. Such as 208Y 120 Volt Three Phase Four Wire OR 480Y 277 Volt Three Phase Four Wire. THERE IS A NEUTRAL
2) OPEN DELTA This is a non often used method to achieve three phase power WITH ONLY TWO INSTEAD OF THREE TRANSFORMERS However it can only produce something like 58% of the power that the use of three transformers could deliver. In all my years of practice I never designed for it.......Its not called Wild Leg when and where I practiced, but I cant speak to the entire USA
3) WILD/RED Leg Three Phase Four Wire: This is similar to 1 above, however one of the three transformers has a center tapped and Grounded Neutral, and its referred to as Three Phase Four Wire (Wild/Red leg) Delta. It is often used if the majority of the power requirement is 240 Volt, Single or Three Phase, with a small amount of power needed for 120 Volt Single Phase. ONLY ONE of the three 240 Volt transformers is center tapped so its 120 Volts from either end to the center tap Neutral....... THERES A LOT OF IT OUT THERE......
BUT NOTE its called Wild or Red Leg because while two legs are 120 Volt to Neutral, the other Wild/Red leg would be 208. DONT USE THAT WILD/RED LEG for 120 Its NOT for Bubba or lay persons but okay for professionals who understand it.
NOTES
A) Wild/Red Leg is a THREE Transformer configuration (see 3 above) NOT a TWO Transformer.
B) The two transformer method to achieve Three Phase, is called OPEN DELTA, NOT Wild Leg when and where I practiced.
C) Wild/Red leg IS USED when most of the loads are 240 Single or Three Phase with a small amount of 120. HOWEVER I instructed my electricians to properly label and identify the (one of the three) Wild/Red legs so a rookie wouldnt use it for 120 volts !!!!!!!!!!
D) If available, three phase operation is preferred and in our plant any motors over 5 HP I specified Three Phase
Sooooooooooo you need at least THREE Wires for Three Phase straight DELTA. (Has NO 120) 3 Hots you need at least FOUR Wires for Three Phase Four Wire Y (208Y 120 or 480Y 277) 3 Hots, 1 Neutral you need at least FOUR Wires for 120/240 Volt Three Phase Four Wire Red/Wild Leg Delta 3 Hots, 1 Neutral you need at least THREE Wires for typical household 120 240 Volt Single Phase Three Wire.
NOTE most straight Delta configurations are FLOATING non Grounded systems. However there can be corner Grounded Deltas. I preferred Grounded systems versus Floating although many were Floating in years past. Im NOT opening that can of wormss here lol
Hope this helps but no warranty as things or the NEC may have changed since I last practiced, but I believe it to still be true
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