Column-by-Column: Motor Model and Rating

We previously established the wealth of knowledge held in the AIM Manual for contractors and installers and the two pages that stand out (pages 13 and 14). Packed with information essential to single-phase motor installation and troubleshooting, we continue in this post to review pages 13 and 14 column-by-column.

Again, if you are dealing with 50 Hz motors, you will need a 50 Hz AIM Manual. Also, for those dealing with a 3-phase motor, please reference the table on page 22 of the AIM Manual. This series will focus on Franklin single-phase submersible motors.

Continuing from our last post, working across table 13 on page 13 of the AIM Manual, the second column is labeled the motor model prefix or motor model number. Franklin Electric submersible motors have 10 digit model numbers, this column contains the first 6 of those. Each of these numbers means something, but it’s not important to know what they mean. After all, that’s why the motor rating, voltage, and hertz are etched on the nameplate.

In general, the beginning digit (2) designates a submersible motor. The middle
digits designate the overall electrical design (3-wire for example), and the last signifies 4- or 6-inch motor.

The three digits in the middle designate voltage, hertz, and horsepower (hp) rating. For the AIM Manual, those first six digits are all the information needed to know the motor type. The last four digits that can be seen on the nameplate (not in the AIM Manual) and are internal to Franklin Electric, these incremental changes in the design of the motor.

Moving along, the next two columns provide power rating of the motor in both horsepower and kilowatts. Horsepower is the English measurement and a kilowatt is the metric measurement. When it comes to conversion rates, 1 hp is equivalent to 0.75 kW.
So, a 10 hp motor is 7.5 kW. However, for those working in English measurements the kW column is unneeded.

Let’s turn our focus to a better understanding of the power measurements in these motors. As the name implies, horsepower is a measure of power, and in this case, we’re talking mechanical power delivered by the motor shaft. (We’ll talk about electrical power later in this series.) The horsepower delivered by the motor shaft to the pump is a combination of torque and rpm. Since all of these motors turn at 3450 rpm, a 2 hp motors delivers twice the torque of the 1 hp motor.

This is where things can get confusing. Franklin submersible motors can deliver more than their rated horsepower. This additional horsepower is called service factor and varies with motor rating. The service factor for each motor is found in column seven. The ½ hp motor has a 1.6 service factor. This means that this motor actually delivers a horsepower of ½ x 1.6 for a value of 0.8 hp. The service factor of the 1 hp motor is 1.4 for a total of 1.4 hp. However, all of this is somewhat transparent because the pumps are generally designed to use all of the horsepower available. So, it would be a rare occasion that one would need to know what the service factor was on a given motor.

The final three columns under rating are self-explanatory. They are voltage, hertz, and the service factor we just talked about.

In summary, looking at these first seven columns in table 13, 99% of the time the only references needed are the motor type (2-wire for example), horsepower, and the voltage (if ½ hp). These three items tell us which row we need to be in. Stay tuned for the next post when we explore the next columns, which involve FULL LOAD and MAXIMUM LOAD These will merge right into the service factor discussion above.