120 volt single phase motor

[almaino]

What is the correct way to wire a 120 v single phase motor thru a 3 phase motor starter.

 

[templdl]

What is the correct way to wire a 120 v single phase motor thru a 3 phase motor starter.

Use the 2 outside poles. But, read the starter instructions as a "starter" infers a contactor and an OLR. Pay attention to the OLR as it may not function properly to provide motor overload protection.
But also remember the a 1ph motor commonly is provided with an integral internal thermal protective device aanyway so the OLR should not be required anyway. Thus, a simple contactor would suffice.

 

[kwired]

For basic motor control - you only need to break one conductor.

Overload protection - if it is one designed to monitor for phase loss - you will need to use all three poles, or the phase loss protection will trip. there is more then one way to do this - but most common way would be something like running the ungrounded conductor to L1 and the grounded conductor to L3, running a jumper from T1 to L2, and connecting the motor to T2 and T3.

Also thermal overloads though will not directly detect phase loss, are designed with the heat of each element taken into consideration and you either need to use all three elements for the greatest accuracy, or find the right overload selection chart for when either single or two elements are being used.

 

[Jraef]

...
But also remember the a 1ph motor commonly is provided with an integral internal thermal protective device aanyway so the OLR should not be required anyway. Thus, a simple contactor would suffice.

:thumbsup:

Pretty much true up to and including 1HP at 120V, the OP never said the size. But beyond that, all bets are off, you must check to make sure.

And "... remember..." implies that he knew that in the first place! :roll:

So almaino, to clarify the points raised in these two responses:

1. The real difference is only in the wiring of the overload relay, the contactor only needs to break one pole in a 120V circuit.
2. You may not NEED an overload relay if the 120V motor is small, just look at the motor nameplate and if you see the words "Thermally Protected", or "TP", or something similar, you do not need an OL relay.
3. If you do, or you are using a motor starter in which the OL relay cannot be separated, then the TYPE of OL relay will make a difference in how you wire it.
4. If the OL relay is of the NEMA type that has replaceable heater element inserts that you must select, then you can simply run the power (L1) wire through 1 pole of the contactor and OL relay to the motor, and connect the Neutral directly to it.
5. If it is an IEC (European) motor starter where the OL relay has an adjustable dial, then those are sensitive to phase current loss, which means all 3 poles must have current flowing through them. You cannot split the current flow, it must be the full amount through the sensors. So you take L1 to L1, which comes out on T1, which you then loop back to L2, which comes out on T2. Then you put the Neutral through L3/T3, and connect your motor leads to T2 and T3.
6. If it is a solid state (electronic) OL relay, how you wire it will depend on whether or not you can turn off the Phase Loss detection. It you can, then do it per #4 above. If you cannot defeat the phase loss trip, then do it per #5 above.