Single Phase motor control question

rta53

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Not specifically a PLC question, though related. Most of our systems (water purification) use 3-phase 208VAC or 480VAC motors for our pumps with combination starter/disconnects mounted locally at the pumps. Occasionally we use small fractional HP pumps at 120VAC. I have yet to find a good solution for a controller/disconnect that is comparable to the 3-phase controllers. I have used small 2-pole contactors or power relays mounted in a small Hoffman enclosure and used just a toggle switch as a disconnect. Works but doesn't look as clean as a combo starter. What have you guys used?
 
We usually use a small three phase starter. Most of the manufacturers show you how to jumper the extra poles for use with single phase.
 
Tom Jenkins said:
We usually use a small three phase starter. Most of the manufacturers show you how to jumper the extra poles for use with single phase.

Yea, that's certainly an option. Just seems a little overkill. Do you use still use an overload relay on the starter even if the motor is thermally protected?
 
For low power single phase motors that have internal thermal protection you don't need overloads - NEC allows just a switch or relay. If it isn't internally protected then yes, we use the overloads.
 
Last edited:
This is a Telemecanique IEC starter designed for use with 1/2HP 120VAC 1PH motor

I have used something very similiar from AB. What did you use as a disconnecting means in conjunction with the relay?
 
Last edited:
Telemechanique, Moeller, or even AB make Manual Motor Starters which are thermal magnetic switches (and Circuit Breakers).

These units are for three phase and are amperage specific, but their instructions show how to loop the single phase motor wire to put the three pole in series so that you don't trip the unit with unbalanced loads.

These manufactures also have enclosures for these individual units which can include an Emergency Stop button.
 
Motor Starters

We use AB 600 series for single phase up to 277 VAC. The AB 609 is good for three phase up to 575VAC 10HP. You could buy the Mags off Square D or AB and mount them in a hammond box and flush mount the switches. This is more expensive and more work but looks good.
Have a good week :)
 

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