Sanitary Centrifugal Pump Motors. What do the Different Frame Sizes Mean?

November 15, 2013
Waukesha S200 Santary Centrifugal Pump

Waukesha S200 Santary Centrifugal Pump with Stainless Steel Motor

At Holland, we’ve been putting sanitary pumps into service for over 60 years. And one thing that every pump needs is a motor. A motor enables one to convert electrical energy into mechanical energy, and when coupled to a pump, move a fluid. We’re going to start putting an emphasis on motors and some of the nuances that you should be aware of when specifying a motor
One of the things that always confused me when sizing pumps or identifying replacement parts was this “motor frame size” designation. Where does that number 182 come from? What does it mean? What’s the difference between a 182 and 184 frame? What does TC stand for? This blog is going to address that.

Industrial motors have changed a lot since there invention by either Nikola Tesla or Galileo Ferraris circa 1887. One of the most obvious changes has been the increase in horsepower and decrease in size. Another important achievement has been the standardization of industrial induction motors by the National Electric Manufacturers Association (NEMA). A key part of motor interchangeability has been the standardization of frame sizes. This means that the same horsepower, speed, and enclosure will normally have the same frame size from different motor manufacturers. This allows motors from one manufacturer to be replaced by another’s.

The first part of the motor frame size we need to understand are the two or three numbers preceding the frame style designation. In sanitary pump applications, most motors are totally enclosed fan cooled, and for the purpose of this blog, we will focus on that. There are two general classifications of motors: fractional and integral horsepower motors. The term “fractional horsepower” is used to cover those frame sizes having two digit designations as opposed to the three digit designations. The frame size generally associated with fraction motors is 56. The derivation of the two digit frame number is based on the shaft height in sixteenths of an inch. You can figure that a 56 frame motor would have a shaft height of 3-1/2 inches. 56 is the largest of the current fractional horsepower motors but can be found in sizes up to 3 HP. For that reason, the name “fractional horsepower” can be misleading.

The next general classification of motor is the Integral Horsepower Motor. This designation generally refers to those motors having three digit frame sizes such as 143T or larger. When dealing with these frame sizes one “rule of thumb” is that the centerline shaft height (“D” dimension) above the bottom of the base is the first two digits of the frame size divided by four. For example, a 254T frame would have a shaft height of 25 ÷ 4 = 6.25 inches. Although the last digit does not directly relate to an “inch” dimension, larger numbers do indicate that the rear bolt holes are moved further away from the shaft end bolt holes (the “F” dimension becomes larger). For instance, a 184 frame has bolt holes moved further away from that shaft end bolt holes than a 182 frame.

After those first two of three digits, the frame designation ends with a letter designation. This is yet another NEMA classification. The first group of motors introduced in 1952 was dubbed “U” frame motors. We don’t see many of those anymore. In 1964 the “T” series of motors was introduced. These are the current standard and should be for the foreseeable future. The “T” is often followed by an additional designation. Here are the designations we often see in the sanitary pump world:

C — The C face frame is the most common designation we see in the sanitary pump world. “C Face” designates a “C” face (flange) mounted motor. This is the most popular type of face mounted motor and has a specific bolt pattern on the shaft end to allow mounting. The critical items on “C” face motors are the “bolt circle” (AJ dimension), register (also called rabbet) diameter (AK dimension) and the shaft size (U dimension). C flange motors always have threaded mounting holes in the face of the motor. The Waukesha C series sanitary centrifugal pump uses this type of motor.  The C face frame motor is normally used to connect to gear reducers that are used on most sanitary PD rotary pumps.

JM — The letters “JM” designate a special pump shaft originally designed for a “mechanical seal”.  These motors were specifically designed for centrifugal pumps.  This motor also has a C face. Waukesha’s 200 series sanitary centrifugal pumps use this type of frame.

H — Used on some 56 frame motors, “H” indicates that the base is suitable for mounting in either 56, 143T, or 145T mounting dimensions.
So there you have it, the mystery of motor frame size solved. Future posts will detail motor enclosure styles, gear motors, VFD usage, and more specific pump applications. Below table shows the standard motor designations for the “T” era motors. You can also visit this link for dimensions of common motor frame sizes. If you have any additional questions, contact a Holland Sales Engineer today.

Motor Horsepower 3600 RPM 1800 RPM
1.5 143T 145T
2 145T 145T
3 182T 182T
5 184T 184T
7.5 213T 213T
10 215T 215T
 15 254T 254T
 20 256T 256T
 25 284TS 284T
30 286TS 286T
40 324TS 324T
50 326TS 326T

 Holland Applied Technologies