OVER-SIZED PUMP/UNDER-SIZED WIRE?

Discussion in 'Pumps and Tanks Well Forum & Blog. Water is life.' started by Jazzman, Aug 22, 2019.

  1. Jazzman

    Jazzman Member

    Joined:
    Oct 14, 2015
    Location:
    Oregon City
    I was helped on this site sizing pump for low -producing well that is 358’ deep. I ordered 3/4 hp 5 gpm Flowise submersible and #12 gauge wire. However, the supplier substituted a 1 hp 5 gpm pump without telling me. The 1 hp pump is rated maximum for 400’ for #12 wire and I’m at about 420’ from sub-panel. I’m way out in the country ready to install but wondering if I should hold off and get correct pump. Also, I’m pumping into storage tank and I will have only 25 gallons of water above pump in casing. Is this 1 hp pump too big?

    Thanks!
     
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    740 ft of #12 is even too light for 3/4 HP.
     
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  4. Jazzman

    Jazzman Member

    Joined:
    Oct 14, 2015
    Location:
    Oregon City
    Hi, the distance from sub panel to pump is 420’ not 740’.
     
  5. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Ahh... You were including ~ 338 (down to the pump) in your number 420 number. I misinterpreted.

    Yes, the AIM manual says #12 is good for 400 ft with 1 HP vs 480 for 3/4 HP. Also, you may need to account for drop to the subpanel. I am not sure. It's close, but the AIM manual numbers would have some margin built in.

    A 3-wire pump will draw less power through the breaker during starts and if it has a run capacitor also, it draws a little less power while running. The AIM manual does not seem to get that nuanced in Table 11.
     
  6. Jazzman

    Jazzman Member

    Joined:
    Oct 14, 2015
    Location:
    Oregon City
    Thank you so much for the detailed clarification. It is a 3-wire Pump. I also thought that it is important to size pump to well recovery rate and my well recovery is not quite 1 gpm. Bigger isn’t necessarily better from what I’ve read. It am at remote cabin with pump in hand, so I’m tempted to drop it in well...
     
  7. valveman

    valveman Cary Austin Staff Member

    Joined:
    Mar 15, 2006
    Occupation:
    Pump Controls Technician
    Location:
    Lubbock, Texas
    20' extra will be fine. As long as the total length is 420' then #12 will work, barely.
     
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Forum Title Date
Pumps and Tanks Well Forum & Blog. Water is life. Throttling back an over-sized pump Sep 23, 2009

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