Motor starter

Krispunkle

Member
Location
Indiana
I have a 120v motor, and a 3 phase motor starter was sent to me for the job, i just wire the lines and terminals in series and t3 to motor as hot, and bypass neutrel straight to motor to make everything work? Because all three overloads would need power correct?
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
Yup.
Sounds like an expensive mistake.
IEC style starters are not usually available with single phase overloads, due to limited volume.
Wiring all three elements in series is the preferred solution, such as line in->L1, T1->T2, L2->L3, T3->Motor out.
 

Krispunkle

Member
Location
Indiana
They also sent me 2pole breakers for the job, I think no one knew the motor it's feeding is only 120v. So now it's just overkill. I only need one hot. I've just never had to wire a Motor stater three phase down to only needing one hot. Usually have the right stuff for the job.
 

Krispunkle

Member
Location
Indiana
IEC style starters are not usually available with single phase overloads, due to limited volume.
Wiring all three elements in series is the preferred solution, such as line in->L1, T1->T2, L2->L3, T3->Motor out.
Thanks I was wondering that, because I need overloads for this application, I'm sure that's why they sent this starter, I appreciate the help guys.
 

kwired

Electron manager
Location
NE Nebraska
Is contactor and overload sized for the motor it is driving? If sized for a 240 volt or even a three phase motor of the same horsepower it could be too small to handle the 120 volt motor.

It doesn't hurt to run the neutral through the contactor and overload, as long as any interruption of the neutral is simultaneous to interruption of the ungrounded conductor, but also isn't necessary.

You only have to use all three poles of the overload if it is a type that is designed to detect phase loss, or if accuracy of the device depends on heating from all three units. Melting alloy overload units usually use a different selection chart for a single element than for multiple elements in the same enclosure, check the instructions of the overload unit for settings or element selection.
 

norcal

Senior Member
Another question is what voltage is the starter coil? Assuming that it is a magnetic starter.
 

masterinbama

Senior Member
IEC style starters are not usually available with single phase overloads, due to limited volume.
Wiring all three elements in series is the preferred solution, such as line in->L1, T1->T2, L2->L3, T3->Motor out.


This is the preferred method, used to have this come up on water and sewer plants. Chemical vendors are notorious for changing motor voltages and HP's.
 

Aleman

Senior Member
Location
Southern Ca, USA
Is contactor and overload sized for the motor it is driving? If sized for a 240 volt or even a three phase motor of the same horsepower it could be too small to handle the 120 volt motor.

It doesn't hurt to run the neutral through the contactor and overload, as long as any interruption of the neutral is simultaneous to interruption of the ungrounded conductor, but also isn't necessary.

You only have to use all three poles of the overload if it is a type that is designed to detect phase loss, or if accuracy of the device depends on heating from all three units. Melting alloy overload units usually use a different selection chart for a single element than for multiple elements in the same enclosure, check the instructions of the overload unit for settings or element selection.
That's what I would do, wire the line and neutral and leave one leg empty. With most starters this will be no problem.
 
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