Pump Motors are sized to the pump capacity when purchased together. But are you getting the right motor for your application? There are several factor to consider. Inside, outside, voltage, service factor, frame, etc.
Inside or Outside application
If you are going to put your pump outside you have two options, Put the pump in an enclosure or get a totally enclosed non-ventilated motor on you pump. My preference is to put your pump/motor in an enclosure. Why? Typically you have more than just a pump/motor combination. There are several other controls that start and stop the pump and they need protection.
Putting you pump/motor outside has its variables also. Will it be in the sun or shade? The total enclosed non-ventilated motor is a sealed motor that can get wet and still run fine but it will not run long under water. Not many motors are designed to be in the sun. The price is high. Keep you motor in the shade.
Totally Enclosed Motors
Total enclosed non ventilated motors typically have a high service factor which means they can run in extreme conditions of heat, but constant sunlight in a plus 100 degree weather is another story. All motors have an ambient temperature rating, check the specs. Many times specs are in Celsius. A 40 degree Celsius is typical for a totally enclose non-ventilated motor. 40 degree Celsius equals 104 degree Fahrenheit. Some are 50 degree Celsius which equals 122 degrees Fahrenheit.
Some motor are classified as Severe Duty. Severe duty give the motor extra protection from the environment. Gasketed terminal box and shaft protection are typical with severe duty motors. Severe duty are not hazardous motors. Hazardous duty motors have a explosion proof element to them and are meant for industrial envrionments where specific gases and vapors exist.
Totally enclosed fan cooled is an option when protected well and in the shade. It can get a little wet occasionally but not drenched. The motor is open at the end where the fan is for cooling. Getting wet while running is not good.
Frame, Mounting Face
Pump Motors have a specific purpose. They are designed to attach to pumps. They couple together. That means the motor has a flat face with bolt holes and shaft designed for pump mount.
Frame mount is typical for pump motors. Meaning the motor has a rigid metal base welded to the motor shell. Some sort of isolations is recommended when bolted in place. Rubber pad or bolt hole isolators are typical.
Continuous Duty or Not
One of the main decision points to make when deciding on a pressure pump is, will it be continuous duty rated or not. Continuous duty means you can run the pumps for long periods of time without shutting it down. Allot of pumps are rated for continuous duty but allot are not. If you see a pump assembly with a timer on it that a good indication that it is not continuous duty rated.
Service Factor, Insulation Class, Thermal Protection
You will see these ratings in motor specification sheets. These are the ratings the tell how heavy duty/continuous duty/severe duty the motor really is. Thermal protection is a nice feature. if you over tax your motor, heat build up, thermal protection will shut it down.
A good place to look at all the different kinds of motors available is to go to Grainger.com and look up motors. The motors we are discussing here have the base classification of pump motor.
Pump Sizing Chart