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I have a Mars 780 61347 two pole 30A contactor:

Mars 780 61347

I am using this contactor to control a 220V well pump that fills a cistern. I then have a float switch in the cistern which, when closed, should cause the well pump to kick on and fill the cistern.

I have a 30A 2P breaker in the box that feeds the bottom of the contactor. The top of the contactor is wired to the pump. If it matters, these wires are attached to the contactor using the screws and not the gold contacts that can be seen in the picture.

The contactor has two silver contacts on it that appear to be for energizing the coil, one on each side. How do I wire the float switch into this setup?

Thanks in advance.

Float Switch

If it matters, the float switch I have is a SJE Pumpmaster:

http://www.sjerhombus.com/ses-controls-float-switches-details.php?ID=50&ID=49

The Rest of the Story

I wanted to respond to some of the comments for posterity's sake.

If you don't know what "in series" means, you probably shouldn't be doing electrical work.

I understand what it means in general but was somewhat confused by this setup and how to apply "in series" to the current situation.

The reality was that I wasn't actually doing the work myself. The guys who dug my well were installing all of this equipment. I didn't always trust the work they were doing so I was asking them to explain things to me. When the installer explained how he was going to wire the contactor, he told me he was only going to have one wire going to the coil and leave the other side without any wire connecting to it. That seemed very wrong to me, but he said b/c it was 220, it would "just work." I highly doubted that and posted here to confirm the correct way to wire it.

By the time he was finished, he realized he made a mistake and had it wired like @Tester101's diagram.

Per Tester101's comment, why are you using a contactor at all? What type and size of well pump (submersible, jet pump) and is it currently hard-wired or plugged-in? Also, what is the model of the float switch you have? Hopefully it's a "PMU" model (pump-up), but they also have versions with and without plugs (which is why I ask). All of these will potentially dictate the best way to wire this up.

I'm using a contactor because the well installers said that is the way it should be done. They explained that the float switch wiring was too small to run the pump's current through that wire. It's a 3/4 HP submersible pump that they have wired using 10 gauge wire. The float switch model is linked to above.

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    What is the coil voltage of the contactor? In general, you just wire the switch in series with the hot lead to the contactor coil. – R Drast Sep 11 '15 at 18:37
  • @RDrast: based on the information in the link below, I believe the coil voltage is 208-240. Can you be more specific about what "in series" means in this situation? Thanks. marsm-a.com/images/MARS%20780%20Booklet.pdf, – Randy Syring Sep 11 '15 at 18:46
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    @RandySyring If you don't know what "in series" means, you probably shouldn't be doing electrical work. In general, the circuit will look something like this. Though you may need a resistor in line ("in series") with the coil. The documentation for the float switch says it can directly control a 1 hp pump at 230V, so I'm not sure why you're using the contactor at all. – Tester101 Sep 11 '15 at 19:24
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    You might be able to simplify the setup, and remove the contactor. Then you'd wire it up like this. – Tester101 Sep 11 '15 at 19:42
  • Per Tester101's comment, why are you using a contactor at all? What type and size of well pump (submersible, jet pump) and is it currently hard-wired or plugged-in? Also, what is the model of the float switch you have? Hopefully it's a "PMU" model (pump-up), but they also have versions with and without plugs (which is why I ask). All of these will potentially dictate the best way to wire this up. – gregmac Sep 11 '15 at 23:33
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In general, the circuit will look something like this

pump circuit

Though you may need a resistor in line ("in series") with the coil.

The documentation for the float switch says it can directly control a 1 hp pump at 230V, so I'm not sure why you're using the contactor at all. You might be able to simplify the setup, and remove the contactor. Then you'd wire it up like this

in line float switch

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Wire the float switch and contactor coil just as if you were wiring a light fixture controlled by a wall switch. Or, in bad ASCII art:

 ----------[float switch]---------
 |                               |
240V                           [coil]
 |                               |
 ---------------------------------
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The picture below is how the well installer ended up wiring the contactor. Note the real setup has a Pumptec installed between the contactor and well pump. I left this out of the question originally to simply the question and because I knew how it should be wired in.

  • breaker / power source: gray sheathed wire coming into box from the left
  • to Pumptec: black & white wires going up
  • Well pump (from Pumptec): wires coming down from Pumptec and then continue down through the bottom of the box go to the well.
  • Float-up switch: black sheathed wire coming in from the bottom. The black lead is connecting to the left side coil contact and the white lead is connecting to the bottom right terminal.
  • Jumper wire: white wire connecting bottom left terminal to right side coil terminal on the contactor.

The key for me in understanding this was that the contactor coil could be operated off 220v and didn't need a neutral.

wired contactor

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