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high (crazzy) leg

EBEBRATT-Ed
EBEBRATT-Ed Member Posts: 13,442
The "Crazy" or "wild" leg as it is called is tapped off a delta system. On a 230 volt delta system you should have 230 volts L1-l2, L1-L3 and L2-L3. To ground you should have 120 volts except for the wild leg which is 265 to ground. The wild leg cannot be used for 120 volt loads.The wild leg is supposed to be tagged orange. Unless something in the unit is 120 volt it should not matter and the unit should run. Running on 230 volt single phase shouldn't matter. A delta system is primarially for 3 phase loads. Since thhere is no center on a delta system the mid point between two legs is tapped and grounded to create a neutral. This creates a crazy leg from hot -neutral on the leg that is not near the center tap.

Comments

  • high (crazzy) leg

    I'm a tech that been in the field for 14 years and the first time for this. I have a trane 16 seer ac that will not start goes off on lock rotor amps. I checked voltage 119 to ground on one leg.2nd leg 230 to ground. L1 to L2 230. I had electrtion check it out he said is a crazy leg notting wrong. so I called trane thay said to switch the legs at the unit and it should work.when i was working on this one the other ac next to it was running for 3 min. then shutting down. the ac are just 3 weeks old. one leg in box has orange tape on it. the ac units are single phase. I'm going back monday to switch the legs. I dont think it will work. what do you all think.
  • don_185
    don_185 Member Posts: 312
    Crazy leg

    Do you have three phase coming into the building? If not then you may want to call the power company.

    If you do then, you need to tap on to the two legs that are only 110 volts to ground.

    It sounds like somone change the phase at the main panel.That where you would need to go to make changes.

    Tell sparky he wrong.



  • Techman
    Techman Member Posts: 2,144
    crazy leg

    I beleave the unit should start and run properly,even with the "hi leg"You can't use that hi leg on any 120 loads. The orange tape is proper for identifying a hi leg.Is the comp a scroll ?
  • don_185
    don_185 Member Posts: 312
    Techman

    Techman, I hear what you are saying that it should balance itself out and, the sinewave do not change however....

    I have seen the same problem with a few just like the op is having and the only fixed was to lower the breaker off the high leg to the lower legs.

    I'm just glad around here in these parts they have gotten rid of that so called crazy leg,high leg,cost me money leg.

    Would be nice to hear what become of this.
  • World Plumber
    World Plumber Member Posts: 389
    Delta Y system

    The high leg commonly called meg leg in our area. Is used only for 3 phase. Anything conneded to is should be rated 3 phase 440 volt. Three phase motors can run backwards if that happens change any two of the three hot legs around. Be careful not to connect any single phase units to the meg or crazy leg. Or you will soon see the equipment fail. It doesn't take long for the extra voltage to burn things out. If the unit is rated 220V and your supplying 360V. If the supplier know you have a delta Y system and you try to warrenty a fried motor You may get warrenty denied. Check your equipment Three phase W is only 380 volt. Your name plates should read 380/440 volt or 440 volt.
  • high (crazzy) leg

    Thanks for all the info. not sure if the is 3 legs coming in to building. the panel is full the only 2 pole breakes are for 2 ac and one fos subpanel. the units are 220 singal phase. I will be going out tomarrrow 9-28-08 with a call to trane will see what happens will let you all know
    this is in chicago.
  • don_185
    don_185 Member Posts: 312
    Well

    Well let me be the first to say I may be wrong.I can only go on my experience as to what I've seen in the field.

    Techman and Ebebratt are saying it should not be a problem.
    With that said, I would be looking at what else could make the system go out on lock rotor.

    What about the starting device..capacitor,start relay.
    What type of txv? Is there a liquid line solenoid valve?
    Are you sure the service valves are open?






  • Glenn Harrison_2
    Glenn Harrison_2 Member Posts: 845
    Hey Greg, nice to see you on the wall.

    Here's my thought, Those Trane units probably have a one pole contactor, so one of the two legs is energized all the time, creating a poor man's crankcase heater by keeping the windings warm. If the Hot or crazy leg is on the always closed side of the contactor, you are sending much more power thru the windings then they are designed for. By switching the legs as Trane suggested, you are now sending only 120+/- volts thru the windings for crankcase heating, which will not overload the windings.

    Now the problem is the windings have probably been permanently damaged. I would bet you will be changing compressors. Either way, I would get rid of the one pole contactors and install two pole contactors, and real crankcase heaters wired on the inlet of the contactors.
  • World Plumber
    World Plumber Member Posts: 389
    1-3 phase

    If the units are single phase he needs to get the high leg switched at the panel so he only has 110/120 volt on each for 220/240 volt across the two legs. Just switching legs around is not going to correct the problem. 120 and 240 equals 360 volts. If the units are single phase 220/240 that is way beyond the tolerances of 208/250. Even if the units are 3 phase he may have the wrong units. Hopefully they are dual rated as 380/440 Then switching leads around may correct the problem. If the compressors are trying to run backwards, they will reverse direction. On three phase you always need to check that your motors are running in the right direction. If they are not you switch any 2 of the legs.
  • Techman
    Techman Member Posts: 2,144
    What time is it in Chicago?

    O.K. Greg, what did you find out today?


  • Ok have checked it all out. one of the units is running good. not so good for one. after talking to trane (with a call to the factory and 3 people latter) running the crazy lag on a singel phase unit is ok as long as one lag to ground is 120 and the other 220. as long as you dont run the crazzy lag and common. after checking the unit. when the compressor starts the amps stay at 67 runs for 30 sec. then shuts off. suction presure starts to drop around 30 psi high side stays the same. caps are good. potential relay good. (pulled wire 2 off when starting still does samething) talking to trane thay say its the compressor. thay say when we change it check to make sure the txv is ok.and that the crank cassheater turns off. I will let you all know what happens.
    Glenthehvacman. we need to meet up.how is the new job. send me a email at [email protected]
This discussion has been closed.