Originally Posted By: rpalac
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A wild leg in electrical terms refers to the leg or tap on a Delta wound transformer.
These are 3 phase instatations.
This is used in commercial industrial application mostly. The common transformers you see in most construction today are "Y" connected transformers.
If you look at the letter "Y" it explains how the legs and taps are formed. Each outer end of the "Y" configuration represents the end of the coil winding . The center is the ground tap. The length of each leg is set exactly 120 degrees out of phase. .This means that from each leg end to ground you get 120 volts. Between each end you get 240 volts.
On a delta connected transformer the delta symbol looks like a tri-angle. each outer point is the leg tap. You mid tap one coil half way to create the ground tap. This divides one coil in witch you get 120 volts to ground from A leg and C leg. B leg is opposite and you run through a longer coil to get to it so you have a higher derived voltage to ground at around 176 to 209 volts. The wild leg. This leg is always marked with orange tape as part of the color code. If you go between legs you will still get 240 volts between A& C, B& C, or A & B.
Now that voltage is for 120 / 240 Red, Black, Blue for Y, red Black Orange for Delta.
If it is 277/480 it's brown, orange, yellow.
The delta type transformation is for high power demand industrial. If you loose a transformer coil the winding is still completed by the other side of the Delta. There-fore you never loose power. If your light safety system tells you that you lost a leg. You can do the repairs when the system is shut down later. You don't loose production that way.
I've worked on many, many, many of these systems.
Now for a real challenge try 2 phase 5 wire. I have only met a couple of people who work on this system. I was lucky enough to be a trouble shooter for it. Very rare, only found in old city Philly, part of New York, and Chicago that I know of.
If you found this in residential, I can't imagine it.