Submersible Pump Overload After Fifteen Minutes
A 5-inch PVC well is 300 ft deep with a static water level of 90 ft. The well permit lists a yield of 12 gpm. A 1.5-hp, 230-V, three-wire submersible pump is set at 250 ft on 1-inch poly pipe. The pump curve shows 10 gpm at 310 ft of head and 12 gpm at 280 ft. The pressure tank is set at 40/60 psi, and the pressure switch is 2 ft above the tank outlet. The homeowner reports that the pump runs for 15 minutes, then the overload trips; after reset it runs again. The driller measures 238 V at the control box, 230 V at the motor leads under load, and 9 gpm at the hose bib. Drawdown after 20 minutes is 210 ft. The driller proposes lowering the pump to 290 ft and increasing the pressure switch to 50/70 psi to 'give it more pressure.'
1. Diagnose the likely causes of the overload trip. What measurements would you take before changing the pump setting?
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The overload after 15 minutes points to a thermal or current problem, not simply a pressure setting. Before moving the pump, measure running amps on each phase and compare with the motor nameplate; check voltage at the control box and at the motor leads while running, voltage imbalance, insulation resistance, winding resistance, capacitor and control-box compatibility, and the check valve. The 230 V under load is not obviously low, but a 238 V no-load reading that drops to 230 V should be checked against wire size and splice condition. A 9 gpm flow at 210 ft drawdown means the pump is operating near the low end of its curve; with 40/60 psi it may be near 310 ft head, so it should not be badly oversized. The tripping could be a failing motor, sand, a stuck check valve, or a tank/cycling issue. Do not change the setting until the electrical and hydraulic data are complete.
2. Evaluate the proposal to set the pump at 290 ft and raise the pressure switch to 50/70 psi. Include submergence, drawdown, and pump-curve effects.
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Setting the pump at 290 ft is a poor trade. The well is 300 ft deep, so the pump would sit only 10 ft above bottom, increasing the risk of picking up sediment and plugging the intake. The drawdown of 210 ft leaves 80 ft of submergence, which is enough; lowering the pump is not needed for submergence. Raising the pressure switch from 40/60 to 50/70 adds about 23 ft of head (10 psi × 2.31 ft/psi). On the pump curve, that shifts operation to lower flow and higher head, which can worsen heating and does not address the overload. The pump may run longer and hotter. A better approach is to fix the cause: verify motor amps, voltage drop, control box, check valve, and tank precharge; confirm the pump is not rubbing or sand-bound. Any new setting should keep the intake at least 10–20 ft above the bottom and maintain submergence under predicted drawdown.