Power for Pond Pumps
Operating a pond pump maybe two-fold, the first is for aeration of the pond and the second can be for irrigation purposes. Installing the pump correctly will go a long way in the pumps efficiency. The primary wiring for that pump must be of the correct size to deliver enough electrical power to the pump.
Horsepower and Wattage
Most water pump motors are rated by horsepower (hp). Finding the amount of electrical energy required to run that motor begins with the rated horsepower. In general, one horsepower is equal to 746 watts. A 5 hp electric motor then would be equal to 3730 watts. Your monthly utility bill is based upon a term of Kilo Watt Hours (KWH). One kilo is equal to 1000. The 5 hp pump is then equal to 3.73-kilo watts (KW). The hour rating on the monthly bill is related to how many hours electrical devices are under operation. If for example the 5 hp pump runs for 10 hours the amount of power used by the pump would be 37.3 KWH.
Volts and Amperage
Knowing the amount of amperage that is used by the pump motor is important for calculating the correct size of wire for the motor. Most pump motors will be powered by either 120 VAC or 240 VAC from the main electrical panel. The amperage rating for the motor is typically found on the motors nameplate tag. The tag is located on the main frame of the motor. You can also find the amperage by a simple electrical formula where the wattage is equal to the voltage times the amperage (w = v x a). The formula can be algebraically modified to find the amperage directly and looks like (a = w /v). The amperage required for the 5 hp motor using 120 VAC is equal to 3730 watts / 120 VAC = 31.08 amperes. Operating the same motor, but on 240 VAC the amperage will be half that amount at 15.54 amperes. Using the National Electrical Code Book Table 310 we can find the correct wire size for the 5 hp pump.
Wire Size
The length of the wire is as important as the motors amperage rating. A general rule of thumb to be followed is that for every 100 feet of wire, the wire size should increase by one full size. Typically wire sizes and amperage ratings can be classified by a progression in amperage for each full size of wire. A 12-gauge wire will conduct 20 amperes of power safely. A 10-gauge wire will transmit 30 amperes and an 8-gauge wire will conduct 40 amperes of power. A 6-gauge wire will handle a total of 50 amperes. In the above example, the 5 hp pond pump is placed in a pond that is 150 feet from the main electrical panel. According to the NEC book Table 310 we can find that a 12-gauge wire for outdoor ratings will be sufficient to handle the 15.54 amperes. To be on the safe side for such a long run of wire though, it will be best to size the wire one full size larger to a 10-gauge due to the long wire length. When it comes to electrical power it is always better to oversize the wire than it is to make it too small. Using a too small of wire can cause the pump motor to prematurely burn itself out by not receiving enough voltage.
