What is Cause of High Current in New Submersible Pump

Discussion in 'Pumps and Tanks Well Forum & Blog' started by petegerster, May 15, 2012.

  1. petegerster

    petegerster New Member

    Messages:
    5
    Location:
    New jersey
    With a great deal of help from this forum I replaced my jet pump with a submersible. We now have a system that at least from the standpoint of taking a shower is much better than the previous system which we used for almost 40 years. However there is one problem. The current being drawn by the pump motor is 5.1 amperes and the FLA specification is 3.7 amperes.

    Here is what I believe to be the pertinent information:

    MANUFACTURER SPECIFICATIONS
    Goulds Pump - 7GS05422C Motor - M05422-50C211
    There is a ball valve on the pump outlet pipe as it enters the basement which restricts the flow so that the outlet head does not drop below a value which would allow the pump to operate outside its design volume.
    Motor is 2 wire 230 volts - thermally protected.
    Full Load Amps spec - 3.7A
    SF Amps spec - 4.7A
    Winding resistance spec - 4.6 to 5.6 ohms

    TEST DATA ON MY SETUP.
    Voltage at pressure switch during pump operation - 242 volts
    Current - 5.1A
    Total dynamic head at pump outlet - 200 feet
    Volume produced by pump - 8 GPM
    Expansion tank and house distribution system disconnected. One faucet open.
    Resistance of motor leads including 340 ft of 12 gauge copper conductor - 5.3 ohms (measured at pressure switch)
    Resistance from motor leads to ground - greater than 30 megohms (measured at pressure switch)

    After I first installed the system I ran the pump for about 20 minutes under the conditions specified above. I was not keeping careful track of time. I was trying to get the water to run clear. I stopped the test because the water stopped coming out which I interpreted as the pump having emptied the well, so I immediately shut off power to the pump to avoid damage to it. (I have not yet installed a low water shut-off.) In my hurry to shut the pump off I did not note whether it was still running. It may have cut out on high temperature The column of water in the well is about 150 gallons. I turned the power back on. The pump restarted and continued to pump normally. I am unsure how long it was powered off, perhaps 5 - 10 minutes.

    Not understanding the problem I hesitate to run the pump for long periods although when I disinfected the well the pump seemed to operate normally, except for the high amps, during the chlorine purge phase.

    I have thought about what might be happening and have come up with two possible reasons for the high current. There are probably others which with my limited knowledge I have overlooked.

    (1) A faulty pump. This seems unlikely.

    (2) This is more complicated. Before installing the pump, I fabricated a shroud from 4" thin wall sewer pipe as described elsewhere on this forum, and attached it to the pump using 2 stainless hose clamps around the pump about 4" above the intake. I tightened the clamp screws quite firmly using a socket wrench. At the time I felt uneasy about doing this, but I couldn't think of any other way to attach the shroud to the pump, and I could not find anyone advising against it. The clamps go over what Goulds calls the cable guard which is a longitudinal metal housing covering the wires going past the pump to the motor.

    What may have occurred is that the cable clamps by putting force on the cable guard has distorted the pump body such that it is causing interference between the impeller and the fixed housing of the pump.

    Would anyone please suggest other possible causes of the over-current problem, or if you think the clamps are the source then how does one attach the shroud to the pump? I thought of putting the clamps very near the motor end of the pump housing, but I was concerned that the shroud, when squeezed down, would obstruct the suction of the pump.

    Thank you for any insights you might provide.
  2. valveman

    valveman Moderator Staff Member

    Messages:
    4,418
    Location:
    Lubbock, Texas
    My book shows a 1/2 HP, 240V, 2 wire submersible is good to 6 amps. They always load subs heavy, so max amps are the norm. Don't think you have anything to worry about.
  3. petegerster

    petegerster New Member

    Messages:
    5
    Location:
    New jersey

    Dear Valveman,
    Thank you for your prompt response.

    May I assume from your not having commented on it, that my concern for the cable clamps inducing a slight interference between the housing and the impeller is not valid? If this were to occur it would increase the torque requirement of the pump and the current required by the motor. My thought was that the cable clamp on the cable guard might cause the pump housing to go slightly out of round. I have never seen the innards of a submersible pump so I have no way to judge the stiffness of the housing or the clearance between the housing and the impeller.

    I will try not to worry about it, but I am a worrier by nature. Thanks again.
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,487
    Location:
    Cave Creek, Arizona
    a 200' head of water would create a significant load on the pump motor. Have you looked at the performance curve under different head pressures.
  5. valveman

    valveman Moderator Staff Member

    Messages:
    4,418
    Location:
    Lubbock, Texas
    200’ of “Total Dynamic Head” is the same as a water level at about 85’ and 50 PSI, at which that pump will deliver 8 GPM just fine.

    You will strip the worm gear out of the hose clamp before it gets tight enough to crush anything. But if it did, it would crush the wire on the outside of the pump before it hurt the pump itself.

    The shroud is so good for the motor that it was well worth your efforts.
  6. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,901
    Location:
    NW Ontario, Canada
    An impeller pump is not positive displacement so additional head usually results in less current draw, not more.
  7. petegerster

    petegerster New Member

    Messages:
    5
    Location:
    New jersey
    I would like to thank everyone who responded to my post, especially valveman, whose advice I plan to follow.
  8. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    I'll add that using pull ties of nylon is safer. And when you use a ton of them to tie the wire to the drop pipe, and you leave them LONG, they become standoffs that cant catch anything.
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