[arsparky]

Someone I know had an interesting thing happen and I am seeking an explanation. 4-460volt 3phase motors connected to separate overloads on one starter. Each time he started, the third motor would run backwards. He switched two of the lines at the starter and they all ran correctly. Can anyone explain this?

 

[gnuuser]

the leads he switches went to the overload of the third motor by the sound of it:laughing:

 

[just the cowboy]

Thats how you change direction on a three phase motor, change any set of power leads be it on the starter or at the motor or disconnect.

 

[arsparky]

When he swapped 2 of the incoming lines at the starter the one motor that was running backward changed direction the other 3 stayed the same [correct].

 

[JRaef]

When he swapped 2 of the incoming lines at the starter the one motor that was running backward changed direction the other 3 stayed the same [correct].

Either someone observed something incorrectly, reported something incorrectly, heard it incorrectly or they are living in an alternate universe where none of our laws of physics apply.

or...


3 of the motors have VFDs down stream of the motor starter. VFDs don't care what the incoming phase rotation is, they just rectify the incoming AC to DC, then they always put out whatever AC rotation you program them to put out. There are what are called "Drive Motors" where there is a VFD built-in to the motor itself. he might have some of those.

Bad way to control those motors by the way, if that's what he has. The VFDs inside will die an early death being switched on and off like that.

 

[EB Electric]

Someone I know had an interesting thing happen and I am seeking an explanation. 4-460volt 3phase motors connected to separate overloads on one starter. Each time he started, the third motor would run backwards. He switched two of the lines at the starter and they all ran correctly. Can anyone explain this?

I can't explain that! :no: That is either magical or misinterpreted as JRaef suggested. More than likely he switched up the leads T1-T3 or T1-T2 or T2-T3 coming out of the overload to that particular motor. Switching 2 leads on the line side would change the direction of all of the motors ran by the starter. When I hear line on a motor starter I have been trained to recognize line as incoming power circuit L1, L2, L3....