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Why only 2 wires on pressure switch?

Discussion in 'Irrigation' started by bblawncare, Mar 22, 2008.

  1. bblawncare

    bblawncare LawnSite Member
    Posts: 129

    I wired the new pressure switch just like the old one in this pic. But I hate doing things I do not understand (I followed the old setup because I know the company that did it and trust their work). Could someone please help me understand why 4 wires are not used? This is the 5 hp pump I worked on earlier this month. I read somewhere that 2 wires can be used on 3 hp and higher pumps, but once again, I do not understand the difference in the wiring setup. Why would smaller hp use 4 wires? Thanks for any input.:)
  2. AI Inc

    AI Inc LawnSite Fanatic
    Posts: 25,390

    4 wires is 220 , ground /neutral , hot , hot. 3 wires is ground, neutral, hot. Probably didnt answer your question for you , but I guess I realy didnt understand your question.
  3. average joe

    average joe LawnSite Member
    Posts: 4

    I used to do well service and have replaced many pressure switches. The pressure switch is only a switch. When it closes it makes contact between the 2 wires. There are 4 lugs for 220volt pumps because both legs are hot and need to be broken when the pump is off.

    Hope that helps.

    Also the higher horsepower pumps cant be switched directly by the switch. They draw too much amperage. The wires you connected should be connected to a relay with is actually turning the pump on.
  4. Hurrah you are back. I was afraid we had ticked you off with our mean lawn care comments and you had abandoned us.
  5. bblawncare

    bblawncare LawnSite Member
    Posts: 129

    I forgot the pic in my orinal post and forgot to mention that there is a ground wire too. This same property had a new pressure switch installed on there house water supply (1/2 hp) by their plumber, and there are 4 wires connected to the pressure switch instead of only 2 like on the irrigation switch.

  6. AI Inc

    AI Inc LawnSite Fanatic
    Posts: 25,390

    4 wires are because 2 going in , 2 coming out. Just like a light switch.
  7. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,799


    If the pump is 220v, it will have two hot lines. If the pump is 120v, it will only have one hot line.

    If the pump is submersible, then you will have your 220v line run to a control box, and then that will run 2,3 or 4 wires depending on the make and model of the pump out.

    Because of this, the pressure switch has extra lugs.

    Please don't mess with things you don't understand, you could cause the pump to short cycle by installing a miss-configured pressure switch, and then you will owe them a pump.
  8. bblawncare

    bblawncare LawnSite Member
    Posts: 129

    Well, that scares me a little bit now. When I installed this I simply rewired it EXACTLY the way it was wired before as stated in earlier post-by a company whose work I trust very much. After the install I ran thru the system multiple times because I had to adjust the spread on the switch. A couple of zones built up too much pressure and caused the pump to cycle on/off. Once all the zones ran within the pressures, I then ran through the entire sytem 3 more times just to make sure it would operate correctly and each time it did.

    I hope I haven't done something wrong. While I said in an earlier post- "the more that goes wrong, the more I learn" I didn't mean I needed to fry a pump.:dizzy:
  9. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,694

    You may not be showing us everything, if there is another pump relay in the circuit. The idea behind always using both sides of a two-pole pressure switch is that the pump isn't 'live' when it isn't running. Even if the installer is a dummy who mistakes hot for neutral. (and for 220, there isn't a neutral)
  10. bblawncare

    bblawncare LawnSite Member
    Posts: 129

    I think I'm seeing the picture clearer now-in this wider shot of the setup, I realize that the wires going to the pressure switch actually go back over behind the controller-my guess is that there is a pump relay back there and that is where the pump wires are connected. So that means the 3 wires I connected to my pressure switch were the ground, one from pump start and one from controller. Is this right?

    The first thing I did before I started was turn the pump breaker off at the panel. When I tested the voltage at the pressure switch, one of the wires connected to the p/s still showed voltage. I went back to the panel and shut down the breaker for the controller and then my voltage retest showed 0 volts. This is how I came to realize that one of the wires to the pressure switch was from the contoller.

    I do not mean to be an idiot or careless-this originally started out as just a leaking pressure gauge and then it turned into problem w/ pressure switch after the leak was repaired. I really need to find a retired irrigation person who I can hire as a consultant when I come across stuff I cannot figure out. In this case I just figured to wire it exactly as I found it because that wiring had been in place for years. But I still want to learn and understand-not just imitate.

    I appreciate all your guys help and patience!:waving:


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