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Old 04-16-2012, 12:16 PM   #1
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wiring a motor control circuit


I am wiring a three phase motor through a two pole vacuum switch. two lines go through the switch but one line is always hot to the motor. is this proper or is this a safety issue?

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Old 04-16-2012, 03:13 PM   #2
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wiring a motor control circuit


Should be okay as long as there is a disconnect ahead of the controller that interrupts all three ungrounded conductors.

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Old 04-17-2012, 02:26 AM   #3
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wiring a motor control circuit


I am on the same page as Brric mention a disconect switch ahead of it you should not have issue however how big this motour you are hooking this up ?

Merci,
Marc

P.S. it much safer if you have legit tripole motour starter.
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Old 04-17-2012, 07:37 AM   #4
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wiring a motor control circuit


Thanks for the reply. both have confirmed my thought that a hot line to the motor at all times would not be good and that a three pole disconect should be used ahead of the vacuum switch.

It is a one hp motor used on a macerator. the vacuum switch is manual start and used as a cutoff safety when vacuum is lost. This is not something i will be installing or using myself so the problem i can forsee is the user not turning off or forgetting the disconnect after the pump shuts off. Then we are back to the original problem. So, I am thinking some kind of Magnetic starter that the coil is deenergized when vacuum is broken.

thanks again, i appreciate your input.
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Old 04-17-2012, 10:30 AM   #5
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wiring a motor control circuit


You can get enclosed full voltage magnetic starters to do this job. You can use the enclosure to add the switch that starts the vacuum. Provided there is enough room.
So you get a NEMA 1 enclosure, magnetic starter per your motor specifications and the ability to add other control devices.
These enclosed starters are pre-wired at the factory and have a connection diagram for the end user to connect it.
Here is a picture of the starters. You can use any brand you like. The pictures are for an example.
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Old 04-17-2012, 06:52 PM   #6
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wiring a motor control circuit


Quote:
Originally Posted by darrelf View Post
I am wiring a three phase motor through a two pole vacuum switch. two lines go through the switch but one line is always hot to the motor. is this proper or is this a safety issue?
A 3 phase macerator ? Must be a commercial building or a seriously large home with a toilet below the sewer outlet. Your proposed vac switch wiring would "single phase" the motor. If it is a 3 phase motor ? A magnetic starter needs to be used as shown above and any control wiring should break the control voltage to the starters coil, which will operate the 3 phase starter properly.
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Old 04-17-2012, 07:53 PM   #7
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wiring a motor control circuit


Quote:
Originally Posted by Jeeps View Post
A 3 phase macerator ? Must be a commercial building or a seriously large home with a toilet below the sewer outlet. Your proposed vac switch wiring would "single phase" the motor. If it is a 3 phase motor ? A magnetic starter needs to be used as shown above and any control wiring should break the control voltage to the starters coil, which will operate the 3 phase starter properly.
How would it "single phase" the motor?
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Old 04-17-2012, 08:08 PM   #8
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wiring a motor control circuit


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Originally Posted by brric View Post
How would it "single phase" the motor?
I am wiring a three phase motor through a two pole vacuum switch. two lines go through the switch but one line is always hot to the motor. is this proper or is this a safety issue?

OOps, I need to clean my glasses. I read it wrong. He is breaking two power lines, not one. Sorry.
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Old 04-18-2012, 07:45 AM   #9
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wiring a motor control circuit


Thanks again for the input. The macerator is used to pump the holding tank on a yacht. When the tank is empty vacuum is broken and the contacts open shutting off the pump.

I understand the way to do this is with a magnetic starter in conjunction with the vacuum switch. The vacuum start up is manual, you have to hit the switch and then vacuum keeps the contacts together until the tank empties.

Where I am having trouble is seeing how the contactor gets energized to send power to the pump vac switch. There must be another control circuit for the Contactor coil? Can I use one leg of L1 L2 L3 through another manual switch to energize 115v coil?

Does anyone have a schematic showing me how to.
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Old 04-18-2012, 10:57 AM   #10
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wiring a motor control circuit


Check out the drawing below. Using your pressure switch we can start and stop the motor.
Remove the "Start" button and the "Stop" button. Then insert your pressure switch into the "RED" colored circuit. Use only one (1) pole of the switch.
You will need to rewire the power circuit to match the drawing and incorporate your switch into the schematic.
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wiring a motor control circuit-wiringdiagram1c.jpg  
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Old 04-18-2012, 11:12 AM   #11
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wiring a motor control circuit


This is just what the dr. ordered. thanks JV. and thanks to all.

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