Understanding IEC Motor Nameplates Prepared by: Jon Roberts, 7/2003
Problem Statement: Motor nameplates can be confusing. In fact, it is not unusual for many energy managers/engineers
Solution: This technical paper discusses how to read and interpret International Electrotechnical Commission (IEC) motor nameplates. A companion paper discusses NEMA nameplates.
1. Who Determines What Goes on a Nameplate? Motor standards are established on a country by country basis. Fortunately though, the standards can be grouped into two major categories: NEMA and IEC (and its derivatives). In North America, the National Electric Manufacturers Association (NEMA) sets motor standards, including what should go on the nameplate (NEMA Standard MG 1-10.40 "Nameplate Marking for Medium Single-Phase and Polyphase Induction Motors"). In most of the rest of the world, the International Electrotechnical Commission (IEC) sets the standards. Or at least many countries base their standards very closely on the IEC standards (for example, Germany's VDE 0530 standard and Great Britain's BS 2613 Standard closely parallel the IEC 34-1 standard). The NEMA and IEC standards are quite similar, although they sometimes use different terminology. Thus, if one understands the IEC nameplate, it is fairly easy to understand a NEMA nameplate, and vice-versa.
2. IEC Nameplates GENERAL & CONSTRUCTION DETAILS 2.1
Frame
The "Frame" designation describes the motor's physical frame size and mounting configuration. The frame designation for IEC motors is composed of a two-part letter/number code. The letter portion of the code specifies the physical frame dimensions, while the number portion of the code specifies the general fram size. BOTH IEC and NEMA motors use a letter code to specify the physical frame dimensions. Unfortunately, the codes are different and can lead to confusion. For example, an "K" code for an IEC motor is equivalent to a NEMA "H", whereas an IEC "H" is equivalent to a NEMA "D" The numeric portion of the code (indicating frame size) is less confusing, because there is less overlap with different meetings (an IEC "56" is for subfractional motors whereas a NEMA "56 is from ¼ - 1.5 HP motors).
The IEC also defines a motor's mounting position and connecting flange type by a code. A couple of the more common mounting position codes include B3 for foot mounted, B5 and B5 for footless. Three different flange types are defined: FF, FT and FI flanges. The FF flange has through bolt holes, and is available for frame sizes from 56 to 280. The FT flange has threaded bolt holes and is also available for frame sizes from 56 to 280.
2.2
Design Type
The IEC design rating code describes a motor's speed vs. torque characteristics. The IEC Design codes nearly mirror NEMA Design Types, but with different letters. For example, the most common industrial motor is an IEC Design N motors, which is very similar to a NEMA Design B motor. An IEC Design H motors is nearly identical to a NEMA Design C motor. However, there is no IEC equivalent to a NEMA Design D motor.
2.3
Index of Protection (IP) Code
The IEC uses a two-digit "Index of Protection" code to describe how well the enclosure protects the motor from the environment. The first digit in the code defines how well the enclosure protects the motor from the entry of solid objects (e.g., fingers, dust, etc.). The level of protection is defined below: Digit #1: Protection Against Solid Objects 0 No protection. 1 Protected against solid objects of over 50mm (e.g. accidental hand contact). 2 Protected against solid objects of over 12mm (e.g. finger). 3 Protected against solid objects of over 2.5mm (e.g. tools, wire). 4 Protected against solid objects of over 1mm (e.g. thin wire). 5 Protected against dust. 6 Totally protected against dust. Does not involve rotating machines. The second digit defines how well the enclosure protects against moisture. The level of protection is defined below: Digit #2: Protection From Moisture 0 No protection. 1 Protected against water vertically dripping (condensation). 2 Protected against water dripping up to 15º from the vertical. 3 Protected against rain falling at up to 60º from the vertical. 4 Protected against water splashes from all directions. 5 Protected against jets of water from all directions. 6 Protected against jets of water comparable to heavy seas. 7 Protected against the effects of immersion to depths of between 0.15 and 1.0 m. 8 Protected against the effects of prolonged immersion at depth. These two digits are combined to form a code such as: IP22 or IP54. The IP codes are similar to the NEMA enclosure description. The NEMA designations are more descriptive and general, whereas the IEC IP codes are more precise and narrowly defined. For example a NEMA "Open Drip Proof (ODP)" motor corresponds to an IP22, and a NEMA "Totally Enclosed" motor corresponds to an IP54, a NEMA "WeatherProof" motor to an IP45, and a NEMA "Wash-Down" motor to an IP55.
2.4
Index of Cooling (IC) Code
The IEC uses a letter and number IC code to describe how the motor is cooled. There is an individual code for just about every type of cooling method, from small fan cooled motors to large liquid cooled motors. The code can get quite complex, up to a four-letter, four-digit code. A few of the more common "short codes" are shown below: IC 01
The first digit indicates that there air can flow freely in and out of the motor. The second digit indicates that the airflow is caused by an integral fan, or "self-induced". This corresponds to a standard NEMA open fan-cooled motor.
IC 40
The first digit indicates that the external frame/enclosure surface is cooled (i.e., no internal flow). The second digit indicates that cooling is by convection only without a fan action. This corresponds to a NEMA totally enclosed, non-vented (TENV) motor.
IC 41
The first digit indicates that the external frame/enclosure surface is cooled (i.e., no internal flow). The second digit indicates that airflow over the motor is caused by an integral fan. This corresponds to a NEMA Totally-Enclosed Fan-Cooled (TEFC) motor.
IC 48
The first digit indicates that the external frame/enclosure surface is cooled (i.e., no internal flow). The second digit indicates that the motor is in the airstream of the driven fan or blower. This corresponds to a NEMA Totally Enclosed, Air-Over motor (TEAO).
MECHANICAL OUTPUT 2.5
Rated Power Output
The rated shaft power output at the rated voltage, current and frequency. Units are kW for IEC motors, and HP for NEMA motors. The conversion between the two is 1hp = 745.7 W = 0.7457kW The motor's power output is related to its torque by the following relationship: HP = (torque [lb-ft]) * (speed [RPM]) / 5250
2.6
Full Load Speed (RPM)
The motor's speed when delivering rated rated output power at rated full load torque. Note: Many "high" efficiency motors have higher speed ratings than comparable sized standard efficiency motors. This higher operating speed can actually increase power consumption in centrifugal loads (e.g., pumps and fans). For centrifugal loads, torque is proportional to the square of the speed; e.g., doubling the speed will increase torque by 2^2 = 4. Power is equal to torque x speed, or proportional to the cube of speed. Thus, a small increase in speed can have a much larger increase in power consumption. For example, a 1% increase in speed will result in a 3% increase in power (1.01^3= 1.03).
2.7
Full Load Torque (Torque FL)
The motors rated torque output when delivering the rtaed power.
ELECTRICAL INPUT 2.8
Rated Voltage (Volts)
This is the voltage at which the motor is designed to operate. IEC standard 34-1 requires that motors be able to provide their rated output at their rated efficiency for a voltage range of 95% - 105% of the rated voltage. Manufacturers often rate their motors for a variety of different voltages. For example, a motor can be wound for both 230 and 460 V in which case the nameplate would read 230/460.
2.9
Rated Current (Amps)
The current the motor draws at the rated load when operated at the rated voltage and frequency. Unbalanced phases, under-voltage conditions, etc. can cause deviation from rated current.
2.10 Locked Rotor Current (Amps LR) The maximum current draw when the rotor is held stationary.
2.11 Frequency (Hz) Input electricity frequency at which the motor is designed to operate, typically 50 or 60 Hz. Sometimes the frequency range is given for variable frequency drive applications.
2.12 Number of phases (Phase) Number of AC phases the motor is designed to operate, typically single and three phase.
2.13 Power Factor (Cos ¾, Cos100) The power factor of the motor at full load (Cos100) and at ¾ load (cos¾). The power factor is the ratio of active power (W) to apparent power (VA), and can vary from 0 to 1. High power factors (i.e., close to 1) are desirable. The power factor is also equal to the cosine of the angle formed by the lag between the current with respect to the voltage. For induction motors, the power factor varies with load. The following graph shows the typical variation of power factor with load:
Source: "Fact Sheet: Determining Electric Motor Load and Efficiency," US Department of Energy Motor Challenge Program
PERFORMANCE 2.14 Efficiency The efficiency for IEC motors is usually given at full load (η 100) and at 75% load (η¾). Also, an efficiency rating (EFF1, EFF2, EFF3) may appear on the motor. Refer to the EuroDEEM brochure for more information.
2.15 Duty The IEC designates eight different duty cycles: S1 Continuous duty. The motor works at a constant load for enough time to reach temperature equilibrium. S2 Short-time duty. The motor works at a constant load, but not long enough to reach temperature equilibrium, and the rest periods are long enough for the motor to reach ambient temperature.
S3 Intermittent periodic duty. Sequential, identical run and rest cycles with constant load. Temperature equilibrium is never reached. Starting current has little effect on temperature rise. S4 Intermittent periodic duty with starting.Sequential, identical start, run and rest cycles with constant load. Temperature equilibrium is not reached, but starting current affects temperature rise. S5 Intermittent periodic duty with electric braking.Sequential, identical cycles of starting, running at constant load and running with no load. No rest periods. S6 Continuous operation with intermittent load. Sequential, identical cycles of running with constant load and running with no load. No rest periods. S7 Continuous operation with electric braking. Sequential identical cycles of starting, running at constant load and electric braking. No rest periods. S8 Continuous operation with periodic changes in load and speed. Sequential, identical duty cycles run at constant load and given speed, then run at other constant loads and speeds. No rest periods. In contrast to these eight codes, NEMA designates its motors either continuous, intermittent, or special duty, with the operating duty cycle typically expressed in minutes.
RELIABILITY 2.16 Insulation Class (Insul) A letter designation specifying the thermal tolerance, or ability to survive a specified temperature for a specified period of time, of the motor windings. IES motors use five different insulation classes: IEC winding insulation classes parallel those of NEMA and in all but very rare cases use the same letter designations. Insulation designations • • • • •
Class A Class E Class B Class F Class H
105° C (221° F). 120° C (248° F). 130° C (266° F). 155° C (311° F). 180° C (356° F).
Most industrial-duty motors use Class B or Class F insulation.
2.17 Service Factor (not used for IEC motors) IEC motors do not have a "Service Factor" rating definition. Instead, the temperature rise, ambient temperature and altitude ratings are defined via the kW output rating. If an increased service factor is required, use the next size larger motor.
3. Additional Resources "A Comparison of the Characteristics of AC and DC Motors," A white paper providing a good general overview of AC vs. DC motor differences. www.abb.com/manuals/dr/index.htm#motors. "Glossary of Motor Terms," provides a good overview & explanation of motor terms. www.abb.com/manuals/dr/index.htm#motors. "What Do All Those Things On An AC Motor Nameplate Mean?" A white paper providing an informative description of motor nameplates. www.abb.com/manuals/dr/index.htm#motors. "Electric Motor Nameplate Definitions & Nomenclature," http://www.3dind.com/page7.html "What Do All Those Things on an AC Motor Nameplate Mean?" White Paper, Reliance Motors, from May 1993 issue of Power Transmission Design. http://www.reliance.com/prodserv/motgen/b7095_1.htm
"What Do All Those Things on an AC Motor Nameplate Mean?" http://www.elongo.com/pdfs/MotorNameplate990519.pdf "AC Induction Motor Nameplate Key," Grainger Catalog. http://www.grainger.com/Grainger/static.jsp? page=rc_nameptdatakey.html "NEMA Frame Guide," Grainger Catalog. http://www.grainger.com/Grainger/static.jsp?page=rc_nemafmgd.html "Motor Technical Glossary," Grainger Catalog. http://www.grainger.com/Grainger/static.jsp?page=rc_techglass.html "Fact Sheet: Determining Electric Motor Load and Efficiency, " US Department of Energy Motor Challenge Program, www.oit.doe.gov/bestpractices/mtors/factsheets/10097517.pdf Motor Master+ 4.0 User Guide, www.oit.doe.gov/bestpractices/motors/ US Department of Energy Motor Challenge website, www.oit.doe.gov/bestpractices/motors/ European Commission Motor Challenge website, http://energyefficiency.jrc.cec.eu.int/motorchallenge.htm European Commission EuroDEEM website, http://energyefficiency.jrc.cec.eu.int/eurodeem/ "Electric Motor Efficiency," EuroDEEM program, http://energyefficiency.jrc.cec.eu.int/eurodeem/pdf/motor_brochure_v3.pdf
4. Test Your Knowledge An IEC motor's nameplate has the following designation: "kW: 10". This means: a) The motor uses 10 kW of electricity at the rated output. b) The motor has an insulation rating of code 10 c) The motor has a rated shaft power output of 10 kW. d) b) and c) The IEC Design codes nearly mirror NEMA Design Types, but with different letters. For example, the most common industrial motor is an IEC Design N motors, which is very similar to a NEMA Design B motor. An IEC Design H motors is nearly identical to a NEMA Design C motor. However, there is no IEC equivalent to a NEMA Design D motor.
What does a motor's design type specify? a) The type of duty-service a motor is designed for, such as continuous operation, intermittent operation, etc. b) The physical size and dimensions of the motor. c) A manufacturer's description or model number. d) The relationship between a motor's speed and torque. The IEC has defined several specific design tyeps with characteristic torque/speed curves. What is the equivalent NEMA Design Type for and IEC type "N" motor a) NEMA type A b) NEMA type B c) NEMA type C d) NEMA type D What does the "cos" rating on the nameplate mean? a) This stands for the "Country of Service", and designates which market or country the motor is designed for and any required standards it meets. b) A motor's power factor c) A motor's class of service, such as: explosive environments, wash-down service, submersible, etc. d) A motor's current draw at operating supply conditions.
What does the IP rating define? a) A two number code that describes a motor's protection from physical intrusion (fingers, dust, etc.) and moisture. b) Specifies that the motor has met the International Certificate for safety and performance. c) A two letter code that defines a motor's cooling requirements and operation. d) The number of phases the motor is designed to operate on. What does an IP 22 rating mean? a) The motor is protected from foreign objects 12 mm and bigger. b) The motor is protected from water dripping up to 15º from the vertical. c) The motor is equivalent to a NEMA "Open Drip Proof" motor d) All of the above.
