Things You'll Need
If you know the make and model of the pump, search online for the manufacturers' technical data sheet. This contains details of the voltage and wattage.
If AC electricity powers the pump, use a clamp-on ammeter to measure the current flowing in the wires. This is a non-invasive method keeping you away from live electrical components.
Water and electricity are a dangerous mix. Never work on a pump while standing in water or with wet hands.
Take care when attaching meter probes to live electrical components. Touch only the parts you have to touch and avoid contact with other components.
Electrically powered well pumps may be submersible or positioned clear of the water. Whatever the type of pump, it does the same thing, which is lifting water from the well to ground level. To do this work, the pump converts electricity into mechanical action, and the harder the job, the more electricity it uses. Finding the current, or amps, drawn by the pump necessitates knowing the wattage of the pump and the voltage supplied to it.
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Check the pump housing for a plaque or label stating the technical details of the pump. This includes the wattage of the pump, and may give a value in amps. If you find an amp value, this is a generalization for that particular model, and it is a close approximation to the actual amps drawn by your pump.
Establish the voltage supplied to the pump. Domestic North American power supplies are either 110 volts or 220 volts. There is some fluctuation in the exact voltage. To be certain, set a digital multimeter to auto-ranging voltage. Attach the red, positive, probe to the positive side of the pump power supply, and then attach the black, negative, probe to the negative side of the power supply. Read the voltage on the meter display.
Divide the wattage by the voltage to find the current. For example, if the pump wattage is 2,200 watts, and the voltage is 110 volts, the current is 2,200 /110 = 20 Amps. This is the value of the amps drawn by the well pump.