How to Read Electric Motor Nameplate Data ~ Learning Instrumentation And Control Engineering Learning Instrumentation And Control Engineering

How to Read Electric Motor Nameplate Data

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The nameplate of a motor provides important information necessary for proper ordering, replacement and application. To help in the proper application of electric motors, the National Electrical Manufacturers Association (NEMA) and other bodies like the IEC (International Electrotechnical commission) define some basic design, performance and mounting parameters to aid in standardizing electric motors. These parameters are then coded onto the motor nameplate to give a basic definition of what you have received.
Motor nameplate data can be categorized according to the following parameters:

(a) General Data
(b) Electrical input
(c) Mechanical output
(d) Motor Design
(e) Performance
(f) Safety
(g) Reliability
(h) Construction

Nameplate data is the critical first step in determining motor replacement.  It is a treasury of important information about a motor. If you specify, buy, maintain, or replace motors, you should know how to read them by going through this post.
The following parameters are the minimum information that can be found on the nameplates of single and poly-phase induction motors:

General Data
A typical nameplate also include general information such as the motor's brand name, a "Serial No." or other identifying number unique to that motor, that would let the manufacturer trace the motor back through manufacturing. The nameplate also includes the manufacturer's name, and its principal city and state and "Made in U.k." if U.k -made.
Electric Motor Electrical Input Data
This is the voltage at which the motor is designed to operate. AC motors are designed to operate at standard voltages e.g 460V , 230V.

Single or Three phase AC power lines are commonly used to supply electric motors power.

Input frequency is usually 50 or 60 Hz. U.S. is usually 60Hz while everywhere else is 50Hz

Rated Current or Motor FLA
This is the full load current at rated voltage , frequency and nameplate Horse power(HP).

Electric Motor Code
Is a letter code that defines the locked rotor KVA per Horse power. They are defined by a series of letters from A to V. The farther the code letter from A, the greater the inrush current per horse power.

Electric Motor Type
The use of type is specific to each manufacturer of electric motors. Type could define a motor as being single or three phase or single or multi-speed or may even refer to the type of construction.

Power Factor
This is given on the nameplate as P.F or PF. Power factor is the ratio of the active power (W) to the apparent power (VA) expressed as a percentage. As power factor varies with load, the nameplate power factor is that at full motor load.

Capacitor Correction
Sometimes, the motor nameplate may include the maximum power-factor correcting capacitor size. Nameplate notation would be something like "MAX CORR KVAR" followed by a number. The number would indicate capacitor value in kilovars.

Mechanical Output Data
Horse Power
Shaft horsepower measures the motor's mechanical output rating; its ability to deliver the torque required for the load at rated speed. It is usually given as "HP" on the nameplate.

RPM or Full Load Speed
The speed at which rated full-load torque is delivered at rated power output is full-load speed. It is generally given as "RPM" on the nameplate. This speed is sometimes called "slip" speed or actual rotor speed rather than synchronous speed. RPM means Revolutions per minute.

Electric Motor Design
NEMA Motor Design
According to NEMA, the design of an electrical motor defines the torque and current characteristics of the motor. Letters are assigned the defined categories. Most motors are design B, although the standard also defines Designs A, C, and D. Common headings on nameplates include "Des," "NEMA Design," and "Design." Note that Some motors may not conform to any torque-speed characteristics defined by NEMA. The motor manufacturer may assign them a letter that is not a defined industry standard. In such cases, It is important to check the design letter when replacing a motor in an existing application.

Electric Motor Performance Data
NEMA Nominal Efficiency
Motor efficiency is defined as output power divided by input power expressed as a percentage. NEMA nominal efficiency on a nameplate represents an average efficiency of a large population of like motors. The actual efficiency of the motor is guaranteed by the manufacturer to be within a tolerance band of this nominal efficiency. The band varies depending on the manufacturer. However, NEMA has established the maximum variation allowed. The maximum allowed by NEMA standards represents an additional 20% of motor losses from all sources, such as friction and windage losses, iron losses, and stray load losses.

Service Factor (S.F.)
Motor service factor is a measure of continuous overload capacity. A motor designed to operate at or below its nameplate horsepower rating has a service factor of 1.0. The service factor (S.F.) is required on a nameplate only if it is higher than 1.0. Industry standard service factor includes 1.15 for open-type motors and 1.0 for totally-enclosed-type motors. However, service factors of 1.25, 1.4, and higher exist.

Duty on a motor nameplate defines the length of time during which the motor can carry its nameplate rating safely. Most often, this is continuous ("Cont"). Some applications have only intermittent use and do not need motor full load continuously e.g. crane, hoist, and valve actuator applications. The duty on such motors is usually expressed in minutes

Safety Data
Many motor nameplates have special markings to reflect third-party certification or recognition. Some common markings include CSA(Canadian Standards Association) and UL(Underwriters Laboratories). These markings indicate that the manufacturing system and the motor components meet the standards of and are continually reviewed by these organizations.

Reliability Data
Insulation Class
This is often abbreviated as “INSUL CLASS” on nameplates. It is an industry standard classification of the thermal tolerance of the motor winding. NEMA defines motor insulation classes to describe the ability of motor insulation to handle heat. The four insulation classes are A, B, F, and H. All four classes identify the allowable temperature rise from an ambient temperature of 40° C (104° F). Classes B and F are the most commonly used. NEMA has established safe maximum operating temperatures for motor windings.
This maximum temperature = Maximum Ambient Temperature + Maximum Rise at Maximum Ambient + Hot-spot overtemperature

Maximum Ambient Temperature
The nameplate lists the maximum ambient temperature at which the motor can operate and still be within the tolerance of the insulation class at the maximum temperature rise. It is often called "AMB" on the nameplate and is usually given in degrees C. Note that the ambient temperature is the temperature of the surrounding air. This is also the temperature of the motor windings before starting the motor, assuming the motor has been stopped long enough. Temperature rises in the motor windings as soon as the motor is started. The combination of ambient temperature and allowed temperature rise equals the maximum rated winding

This indicates the maximum height above sea level at which the electric motor will remain within its design temperature rise, meeting all other nameplate data. If the motor operates below this altitude, it tends to run cooler. At higher altitudes, the motor would tend to run hotter because the thinner air cannot remove the heat so effectively, and the motor may have to be derated. Not every nameplate has an altitude rating.

Electric Motor Construction Data
This designation, often shown as "ENCL" on a nameplate, classifies the motor as according to its degree of protection from its environment, and its method of cooling. NEMA describes many variations of motor enclosures. The most common are Open Drip-Proof (ODP) and Totally Enclosed Fan Cooled (TEFC).

The block provided on the nameplate called “Frame” can provide a lot of useful information for motors. The frame size sets important mounting dimensions such as foot hole mounting pattern, shaft diameter, and shaft
height. Examples of frame designation on the nameplate include – 445T, 445TC, 445TD.

Many manufacturers supply nameplate data on bearings, because they are the only true maintenance components in an AC motor. Such information is usually given for both the drive-end bearing and the bearing opposite the drive end. Nameplate designations vary from one manufacturer to another. For rolling-element bearings, the most common is the "AFBMA Number." That is the number that identifies the bearing by standards of the Anti-Friction Bearing Manufacturers Association.