# 3 phase 3x the fla!



## McClary’s Electrical (Feb 21, 2009)

Empowered said:


> Have 3 10hp baldor motors operating from a genset pushing 480 volts. They decided to re route the. Motors from an old genset to this new one. Should be a very simple connection but now on start up each leg draws over 150 amps ( fla is 11.7) for about 30 seconds then the overload on the motor drops out. Breaker stays on! The shaft and fan seem to be spinning without much overloading. Voltage is good.... Any ideas what's going on?


 
Is the motor dual voltage and got wired wrong?


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## Jlarson (Jun 28, 2009)

Someone f'ed up big time. I would look and make sure they are wired up right if they are dual voltage like mcclary's said first.


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## varmit (Apr 19, 2009)

Sure sounds like the motor(s) are single phasing. Maybe something is loose or made up wrong.


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## John Valdes (May 17, 2007)

Do you have three separate starters (contactors) one for each motor? Tell us how each motor is wired. Can you turn the shafts by hand?


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## oldtimer (Jun 10, 2010)

varmit said:


> Sure sounds like the motor(s) are single phasing. Maybe something is loose or made up wrong.


If there is phase protection, the contactor should open, to protect the motor.

If there is no phase protection, it could keep running, but it will burn up very shortly.

I M O. all 3 phase motors should be protected, with phase protectors.


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## John Valdes (May 17, 2007)

I bet the new generator is wired wrong on the output. Under voltage would produce increased current. Measure the output voltage with the motors disconnected. 
He's gone anyway. Maybe a real electrician came along and showed him how to use a meter.


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## markstg (Jun 13, 2009)

Empowered said:


> Have 3 10hp baldor motors operating from a genset pushing 480 volts. They decided to re route the. Motors from an old genset to this new one. Should be a very simple connection but now on start up each leg draws over 150 amps ( fla is 11.7) for about 30 seconds then the overload on the motor drops out. Breaker stays on! The shaft and fan seem to be spinning without much overloading. Voltage is good.... Any ideas what's going on?


Check whether the motor is wired wye or delta than switch. I've found this which caused the motor to trip on OL. Switched the connection and worked like it was suppose to.


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## McClary’s Electrical (Feb 21, 2009)

markstg said:


> Check whether the motor is wired wye or delta than switch. I've found this which caused the motor to trip on OL. Switched the connection and worked like it was suppose to.


 

please elaborate


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## markstg (Jun 13, 2009)

mcclary's electrical said:


> please elaborate


 
We had a 3 phase 480V conveyor motor that was tripping and wouldn't run the conveyor belt. After scratching our heads, we checked the wiring diagram on the motor with the way the electricians had wired the T leads. Found they had wired it Wye, when the wiring diagram called for delta. Reconnected the T leads per the motor diagram and away we went.


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## Empowered (Apr 12, 2010)

mcclary's electrical said:


> Is the motor dual voltage and got wired wrong?





Jlarson said:


> Someone f'ed up big time. I would look and make sure they are wired up right if they are dual voltage like mcclary's said first.



Sorry for the late response was without the internets for a bit. Yes the motor was dual voltage and wired for low v when the source was high. The reason it threw me for a loop was because the farmer was so adamant that the previous genset was 480v, but ya after i burned a few coils and fuses and got mcclary's advice, problem solved. thanks!


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## SparkYZ (Jan 20, 2010)

Never trust the customer, check for yourself. 


Also what difference would wye or delta make for a straight 3 phase motor? Isn't it just line to line to line?


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## Electric_Light (Apr 6, 2010)

markstg said:


> We had a 3 phase 480V conveyor motor that was tripping and wouldn't run the conveyor belt. After scratching our heads, we checked the wiring diagram on the motor with the way the electricians had wired the T leads. Found they had wired it Wye, when the wiring diagram called for delta. Reconnected the T leads per the motor diagram and away we went.


That sounds right. If you wire up a motor wye, it would be basically running on 277v and as such, as an alternative to reduced voltage starting, there are motor starters that wires up motor in wye on startup, then connect over to delta with a centrifugal switch to reduce starting current. 

In the oil field, from what I read, they use weird 830Y/480v system, then use 480v Delta motors would as wye on 830v. 

That distribution system is meant to reap the benefit of reduced I^2R loss of 830v distribution while permitting commonly available 480v motors to be used.


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