Three Phase Size 1 Starter for 120V Single Phase motor ??

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mrrjw

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I intend on using a Three Phase Size 1 Full Voltage Non-Reversing Starter to power up a 120V Single Phase pump motor (1/3HP). I intend on using two of the poles on the Three Phase Breaker and two of the poles on the Contactor for the connection. I also intend on not using the CPT and hooking up the control wiring (120V) of the starter directly to the each phase leg. Will this cause any malfunctions in the operation of the Breaker and/or the Contactor? Does anyone know of any issues that may affect the proper operation of this setup?
 
If the coil is rated for the voltage..because it sounds like when you apply power you will pick the starter up and the item will run until you through the disconnect..Is that correct..Why do it that way if you want it to run when you turn on breaker..you could get the same with a breaker and disconnect and save cash..
 
Most starter instruction sheets that I have seen show bringing one of the output wires (after the overload) back into the 3rd phase input, not just using 2 of the 3 poles.

I also intend on not using the CPT ...
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I too don't understand this.
 
Motor Connection

Motor Connection

mrrjw said:
I intend on using a Three Phase Size 1 Full Voltage Non-Reversing Starter to power up a 120V Single Phase pump motor (1/3HP). I intend on using two of the poles on the Three Phase Breaker and two of the poles on the Contactor for the connection.
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If the motor is 120V as you say your described connection will burn it up. Is the motor actually 240V? I am a bit confused by your control discription but if the motor is 120V or 240V and you have no remote control requirement why not use a single-pole or two-pole breaker and install a manual starter?
 
justdavemamm said:
Most starter instruction sheets that I have seen show bringing one of the output wires (after the overload) back into the 3rd phase input, not just using 2 of the 3 poles.
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This method is normal for electronic and IEC style overload realys because they are often supplied with "phase sensitivity" which cause the relay to trip faster on single phase loading. But if the motor is lightly loaded then this early trip feature is not much of an issue. And this feature is nowhere as sensitive as an phase loss relay.

Traditional NEMA starter overload relays do not contain this feature so they do not need special wiring.

The primary reason for control power transfromers is so control circuits can operate at at 120V or less rather than at line voltage. So if the line voltage is already 120V, there is no overwhelming reason to include a CPT.
 
The reason we are using a FVNR NEMA 1 Starter on this 120V 1-phase application is because the application necessitates DCS control of the motor start/stop. This is a Chemical Injection skid where the DCS has to monitor the process and inject the necessary chemicals when needed. A simple Fused Disconnect or Breaker cannot be managed as such.



Thanks to everyone for their valued input!
 
mrrjw said:
The reason we are using a FVNR NEMA 1 Starter on this 120V 1-phase application is because the application necessitates DCS control of the motor start/stop. This is a Chemical Injection skid where the DCS has to monitor the process and inject the necessary chemicals when needed. A simple Fused Disconnect or Breaker cannot be managed as such.
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Well, of course. ;)
 
This starter will work fine controlling a 1PH 120V motor. You'll only need 1 of the poles. The 120V neutral goes straight through, it need not be connected through a starter pole. It will need to be tapped (wirenut), and landed on the overload switch. (Where the grounded side of the CPT goes now.)

The CPT is not needed, and if fact likely cannot be used anyway. It likely has primary taps for 240/480 only. Simply tie your 120 control voltage to terminal #3, or the hot side of the coil.

You'll likely need to install all 3 heaters, or (depending on brand) the overload relay might not reset.

The flow of control power is as such; from the source (switch, PLC, etc.), to terminal #3. This source must be maintained for as long as the motor is expected to run. There's a wire from term #3 to one side of the coil. The other side of the coil is wired to the overload contact. (N.C.) The other side of this contact goes to the 120 neutral. Yes, the overload relay breaks the neutral, that's just the way starters have been wired for the past century or so.
 
To chime in/reiterate with the others:
  • NEMA Size 1 is good for up to 1HP at 115V, so no problem
  • You should NOT switch the neutral on a 115V circuit. Only switch the Hot leg. If you switch the neutral and the contact goes bad some day in the future, the motor windings will likely find a different path to ground and continue to run, but in a much more dangerous fashion.
  • If your control voltage (coil on the starter) is 120V, then you should NOT use a CPT, just take the 120V from the line voltage you already have. But you should place a fuse in the control circuit (5A is usual) separate from the motor fuse.
  • 99% of small 115V motors like that will have built-in overload protection in the form of a thermal switch embedded in the motor itself. If it does, the nameplate on the motor will say something like "integrally protected" or "Manual" in the section of the nameplate that says "Overload protector". If that is the case, you may not need the OL relay at all and in fact probably should not. It's generally considered bad practice to have 2 redundant protective devices because it can lead to confusion as to which one tripped and then lead to equipment restarting unexpectedly.
  • If that is the case (integral OL in the motor), you can use a much smaller and less expensive device, maybe even a relay, instead of that serious overkill of a starter. Most of the cheap little "ice cube" style 10A relays carry a 1/3HP 120V rating on them. But if you already have the starter, it will be fine.
 
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