Unbalanced Well Pump ??

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  #1  
Old 05-25-04, 07:27 AM
wilber
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Unbalanced Well Pump ??

I could use some advice>

I have a well pump mounted at the well which is quite a ways from the power source. It has an going to it a 3 conductor cable (with ground). The pump is jumpered for 230V. I would like to continue to operate the pump at 230v and add another device (115V) without running another cable.
I am adding an irrigation system and I would like the valve controller to be located at the pump. I am assuming that the controller draws only a little current when switching valves and almost NO current when idle.

If I wire this controller using one of the 230V hot leads and the return, will this hurt the pump motor? Is this called "unbalanced"? Am I an idiot?

Thanks for any input,
Wilber
 
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  #2  
Old 05-25-04, 08:16 AM
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No, you're not an idiot, but this isn't a safe thing to do unless you can use the existing 220V wire to feed a sub panel near the pump. The sub panel needs 2 circuits - 1 220V for the pump and 1 120V 15 amp circuit for the irrigation controller. All in all, it might be less expensive to run a new 120V circuit from the breaker/fuse box or locate the irrigation controller somewhere else. Many irrigation controllers actually have a transformer at the plug and run off low voltage, so you might plug the transformer in somewhere else and run a low voltage wire from it to the controller.

Doug M.
 
  #3  
Old 05-25-04, 11:07 AM
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Connect a 220/120 "step-down "transformer" with a volt-ampere rating that equals the volt-ampere rating of the connected load by a factor of 125%.Make the connection to the 220-volt circuit thu a 2-pole switch so you dis-connect the transformer when ncessary.

Drive a Ground-rod and Bond together one of the 120-volt secondary leads, the Ground-rod, the Equiptment Grounding Conductor in the Branch-Circuit cable, and ALL metallic surfaces.

The 2-wire, 120-volt "secondary" circuit" will consist of one Black wire and one White wire, the White wire connecting to the Grounded secondary terminal. Connect a fuse in series with the other secondary terminal and the Black wire. The rating of the fuse must limit the secondary current to 125% of the current-rating of the transformer.

You can connect a 120-volt GFI Circuit-Breaker between the transformer and the connected load. The rating of the GFI C-B may exceed the required transformer protection rating ( ex.; 10 amps.) but it will povide maximum protection from the shock-hazards that are prevalent in such locations.

Good Luck & Enjoy the Experience!!!!
 
  #4  
Old 05-26-04, 12:13 PM
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I hope you were not saying use one of the hots and the ground wire. That would be dangerous.
 
  #5  
Old 05-28-04, 06:45 AM
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Originally Posted by joed
I hope you were not saying use one of the hots and the ground wire. That would be dangerous.

That is exactly what he meant. This is how the power company and every other grounded secondary is developed from a transformer. A transformer is not only a voltage conversion device, but also an isolation device. The secondary winding of the transformer has no inherant reference to either the primary lines or a ground potential. It is floating. By grounding one leg of the secondary, you are in effect limiting the voltage to ground to the voltage of the secondary.
 
  #6  
Old 05-28-04, 08:04 AM
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Grounding the secondary of a power transformer is not same thing as using a ground wire in a cable as a current carrying conductor. If you want 120 you will need to replace the cable with one that has a neutral wire and a ground wire.
 
  #7  
Old 05-28-04, 11:22 AM
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Originally Posted by joed
Grounding the secondary of a power transformer is not same thing as using a ground wire in a cable as a current carrying conductor. If you want 120 you will need to replace the cable with one that has a neutral wire and a ground wire.
In re-reading the posts, I think that my reply could be misintrepeted. What PattBaa proposes is ok. He is not saying that the grounding conductor is being used as a current carring conductor. He states that the primary of the transformer would be conneted to the two hots. Then one of the secondary legs would be grounded to a ground rod and also bonded to the existing grounding grid, effectively creating a grounded neutral. Then the other leg of the secondary would be the 120V hot line for the valve controller. But to reply to your post, with the above solution, you would not need to replace the wire.

Scott E.
 
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