120/208 three phase

ok guys got a new to me welder, its a miller mp-65e witch is a three phase machine, now when going to wire it up im confused, on the back it has tabs to move around that u can make it 240v three phase or 480v three phase, its set up for 480v three phase now, but I can rember what my shop has, to stupid I gess, my box has 4 wires coming in, 1 is ground, left one is 120v middle one is 208v and right one is 120v, aint this a 240v three phase system??

Yes. 3 phase with a high leg, also called a wild leg.

I stand to be corrected,,,, I think that is called a "Y" 3 phase, as opposed to the "Delta) three phase. CORRECT?

so my system is 240v three phase.......... if so I need to change my welder around because its set up on 480v three phase

I think the high leg is a delta transformer. The Y type I believe would be a 120/240 or 208 without the high leg.

Yup, 120/240 three phase is a delta with a high leg, 120/208 is a wye, fun when folks hook up single phase 120 volt circuits to the high leg, and can't figure out why they burn things up.

It is a real live three phase welder. Sole 480V and 600V welders are single phase .

http://www.manualslib.com/manual/583679/Miller-Electric-Mp-65e.html?page=3#manual

Unless you're the idiot doing the hooking up lol. I changed out a panel and when hooking things back up I put a "heater" on the high leg. I know enough to never trust the labels but I did it anyways. Turns out that someone in the past had taken the heater out and made it an outlet. It was behind some filing cabinets and I couldn't see to check so I assumed. BAD IDEA! Thank gooddness for surge protectors

Electrical and Legal questions draw everyone out and I cant wait to hear Billy Bob and Bubbas answer to this one lol.

You ask "my box has 4 wires coming in, 1 is ground, left one is 120v middle one is 208v and right one is 120v, aint this a 240v three phase system??

SHORT ANSWER, YES

Okay now listen: From what you say, what you have is correctly in the Engineering and Electrician trades referred to as 120/240 VOLT THREE PHASE FOUR WIRE CENTER TAPPED HIGH/RED LEG DELTA.

On that system the three outer transformer Delta connections represent 240 volt three phase.

Each of the three transformers are 240 VAC Single Phase Line to Line, or 240 VAC Three Phase Outer Delta corners to outer Delta corners

HOWEVER one transformer is center tapped such that from Neutral (center tap of the one transformer is earth grounded) to either outer leg of that transformer, its 120 VAC (1/2 of the 240 since tapped in center).

From the other corner of the delta (The Red/High Leg) to Neutral its 120 x the square root of three (1.732) or 208 volts.

SO IF THE WELDER CAN WORK ON 240 VAC THREE PHASE YOU CAN POWER IT FINE.

NOTICE: This is NOTTTTTTTTTTTT the same as a 208Y120 Volt Three Phase Four Wire Y. That system has 208 Three phase plus three legs of 120 VAC Line to Neutral.

Not sure if non electricians understand this or if Billy Bob or Bubba do, but based on what you said (if its correct) and you have 4 wires and its 120 line to Neutral on 2 legs but 208 line to Neutral on one, then what you have is again correctly referred to in engineering terms as 120/240 Volt Three Phase Four Wire Center Tapped Red/High Leg DELTA

Got it Billy Bob and Bubba?????????

John T BSEE,JD Retired Electrical Engineer

"I stand to be corrected,,,, I think that is called a "Y" 3 phase, as opposed to the "Delta) three phase. CORRECT? "

NOOOOOOOOOOO that's INCORRECT Its a 120/240 Volt Three Phase Four Wire Center Tapped Red/High Leg DELTA

See my post above for more info

Best wishes hope this helps

John T

Greg, you state "I think the high leg is a delta transformer"

THAT PART IS CORRECT.

"The Y type I believe would be a 120/240 or 208 without the high leg."

THAT PART IS INCORRECT

A 208 Y 120 Volt Three Phase Four Wire Service HAS NO 240. Its 208 Volt Three Phase or three legs of 120 VAC Single Phase to Neutral

See my post above for more info

Best wishes hope this helps

John T Retired EE

I was just going to ask him what the heck is wrong with his power. Most everything I work on in three phase is Y or delta. 208 or 240 all the way around. One time we had 208 208 480 on line when a tap in the transformer shorted out. Blew up every cooling fan in several pieces of equipment. The really crazy stuff that sounds something like what he is getting is in south Philly. PA. They have TWO phase. boy is that crazy with four and five wire systems. Heard St.Lewis and some where else has it. Also just like four years ago they had a couple of buildings in the Wall St. area of New York that were still running on DC power. All gone now. Edison was WRONG!!! Tessla and his partner Westinghouse had it right.

now that u have broke it down I see, its my grampa shop nd his big three pahse welder took a crap so I bought us a new to me used welder grampa hooked it up and it powers up but not stong, like it don't have enough power, and am clueless on why it don't seem to work until I seen the back door say 240v nd showed were to put jumpers and 480v nd showed were to put the jumpers, welder came from a big factory, and its jumpers are set on 480v now, so after reading what u had explained I see that its not getting enough current from my 120/208/120 system. im new to three phase and I hate wiring, so trying to lean, thanks

Yeah, I wanted to call it a center tapped delta but when I typed it in my confidence in my memory went away and I couldn't convince myself that I was 100% correct. I used to wire with a guy that knew all this stuff and he tried to teach it to me, but I've never done enough commercial/industrial to need to remember all that knowledge. Thanks for straightening it up John

Troy, you now state "I see that its not getting enough current from my 120/208/120 system."


I guess you realize that system has 240 VOLTS THREE PHASE ?????????? Its NOT 208 Three Phase. The ONLY 208 is the Single Phase Red/High Leg to Neutral. YOU HAVE 240 THREE PHASE

If the welder has taps or wiring changes so it can work on EITHER 240 3 Phase or 480 3 Phase, just change it for 240 VAC Three Phase and it should work fine

If you read my post below it may help you understand

Best wishes and good luck

John T Retired Electrical Engineer

Youre welcome Greg, glad to help

John T

Some places still use 2 transformers (versus 3) for a sort of an Open Delta, but I NEVER specified that system.

John T

The decal should explain how to place the metal tabs. If the decal is not legible then it is in the manual.There should be a combination for that voltage but I am going to check with Miller.

Here is a chart for 230 v .Set jumpers to 230 v.
Note this is not your model { my google is not working well today.]
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