Water Pump Electrical Systems and Meters

The flow of electricity is like the flow of water in your water pump. The voltage is similar to pressure and amperage is similar to gallons per minute. Resistance in the wire is similar to the friction loss in a pipe. These values can be combined in both series and parallels to achieve the desired effect. A hole in a pipe causing a leak is similar to a ground fault which leaks electricity. Wattage or load is similar to flow and pressure combined, and measured in watts. There may be similarities, but there's one big difference: a hole in a water pipe will get things wet, but a hole in insulation can result in an electrical shock hazard. 

One important difference between water and electric systems is that an electrical system is closed – that is, the flow of a current should never lleave the system. If it does leave the system, that's called a ground fault. A water system, however, is open. In most cases, we discharge the water and it leaves the system. 

In your water pump motor's electrical system, the AC voltage will be in the form of alternating voltage. Most residential power is single phase, which is typically indicated by the single sine wave, with a voltage alternating between a positive 120V to negative 120V, 60 times a second. This form of power allows us to raise or lower the power with a transformer which isn't possible with DC electricity. 

Three phase power is used in variable speed drives and industrial applications. This power has 3 sine waves, all 120 degrees out of phase with each other and alternating positive to negative just like the single phase. Besides the simplicity of three phase, the motor requires less copper wire to carry the same amount of wattage as single phase. Voltage is the amplitude of the electricity measured in volts. Most voltage at the site in North America is 120, 240, 480, and 600. The higher the voltage, the less copper wire needed to supply the same amount of power to the load. Power loss in the wire is dependent on the voltage and wire size, which will become resistance for the current. This is the reason power lines throughout the country are high voltage, sometimes as high as 765,000V. 

For example, say you change 120V to 240V through the same wire, we'll have twice the wattage capability at the other end. The motor unlike a resistive load draws higher amps at both high and low voltage relative to the voltage rating of the motor. In a resistive load, the higher the voltage, the lower the amps. By reading the voltage going to the motor, we can tell if the voltage is adequate for the motor to run. We'll cover this below when we discuss meters in more depth. 

As voltage passes through an object, there's a drop in th voltage due to resistance. This is true for AC and DC. A set of contacts in a switch will show a minor drop across them when closed, and full voltage reading when open. This fact can be used to test overloads to see if they're open or closed when power is being supplied. 

With multiple loads and series, the loads will share the voltage, and depending on the proportions of the loads, the voltage could be half on each load. 

Consider a series of switches where you apply multiple switches to control or power a device. If either of the switches is open, the circuit will not be energized. The load will not be energized unless both switches are closed. This may be applied to a pressure switch and float switch when the tank is calling for water. The pressure in the line indicates the pressure is satisfied, and even though the tank is empy, the pump won't run at this time. 

Another scenario would be that the float switch is saying the tank is full, but the pressure switch sees low pressure and tries to run the pump. The pump won't run unless both switches are closed. Now as an example, consider an illustration of parallel switches where you apply multiple switches to control or power a device. When both of the switches are open, the circuit will not be energized. This may be applied to two float switches in a tank where we want to use up most of the tank before we refill, and have both switches open before we shut the tank down. This is an example of switch priority and can be combined with series switches on one or both sides to make sure all desired priorities are met. 

Measuring With the Right Meter

When troubleshooting pumps and motors, meters are critical to analyzing what's going on at your jobsite. A voltometer, clamp on amp meter, and a megger are all necessary meters to troubleshoot, whether your pump is single or three phase. 

Volts are measured with a voltometer. To use the meter, turn it on and turn the knob to the "V" with a wavy line, indicating alternating voltage. With most digital meters, you don't have to worry about the range since they automatically adjust. Accurate readings are important, so keep your meter calibrated on a routine basis. 

To measure the amps in a wire, the best instrument is a clamp tight meter, which can read most currents without damaging the meter. This meter doesn't have to be wired into the circuit – you simply clamp the meter around the wire you want to measure. 

Using a voltometer to read resistance int he best way to check motor windings and wire. To operate the meter, turn the knob to the upside down horseshoe. Once again, most meters will auto-range, so you don't have to figure out where to set the range. When checking a circuit, make sure the power is off, and the capacitors have drained of voltage or the meter may be damaged.

The meter has to have the capability to read the value you're looking for. Know what your meter can do before attempting to take any readings. If the meter isn't capable of the value you're looking for, the reading may mislead you to a wrong conclusion. 

When testing for a ground fault or failure of insulation, a megger is a must. To test insulation on a wire motor, voltage higher than the voltometer can provide is needed. Many pump manufacturers recommend tests be run at 1000V. To run the test, hook your test leads between the power leads you want to check and the green ground wire. The reading may be in millions of ohms since the test voltage is 1000V. Use the alligator clips to hold the test leads to the wires. A ground fault is more than a problem with the system – it's a danger to the user. 

Electrical Relationships

The longer the wire, the greater the resistance. Therefore, the greater need for larger wire. In conclusion, remember that the balance of voltage and amperage in the circuit will ensure a long and proper life to the motor. 

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