3- Phase Starter Controlling 1-Phase Motor

[faresos]

Hello Everyone,

I'm reviewing a submittal where the contractor has submitted a 3-phase combination full voltage magnetic starter to serve a 120V fan motor. Not sure why they did that or it just simply they submitted the wrong starter, Is there any special wiring they need to do to make it work?

 

[Frank DuVal]

Just use two of the three phase contacts and set the overload setting to match the motor nameplate amps.

If the contractor bought the starter from a place like Automation Direct, they don't have single phase starters, so the three phase would be cheaper than buying a single phase locally.

 

[bwat]

Check the manufacturer docs. Some that I have seen are ok to use with single phase also but they want you to do a loop with the wiring and use the neutral IIRC.

Edit: I see Frank posted first. I believe AD even wanted the loop wiring that uses all 3 contacts for the OL.

 

[cpickett]

most of the time you have to loop one motor lead through the third phase of the OL so that it doesn't trip on phase imbalance

 

[jim dungar]

For most IEC style overload relays you need to make sure current flows through all three elements. So for single phase loads you can use:
option #1 (preferred for L-L loads) - Take the incoming hot wire into L1, come out of T1, loop back up to L2, connect load to T2, take the other incoming wire to L3 and connect the load to T3.
Option #2 (preferred for L-N) - Take the incoming hot wire into L1, come out of T1 and loop over to T2, come out of L2 and loop over to L3, connect load to T3, take the incoming neutral wire directly to the load neutral.

 

[faresos]

Thank you all for your responses and thoughts, that was very helpful!

 

[Jraef]

There is nothing wrong with it other than the potential damage to your bank account. It could be done so much less expensively for a 120V motor circuit...